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__________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 2 of 45 May 15, 2012 Copyright © 2002-2012 Table of Contents Table of Contents ........................................... 3 Commands & Programs - Alphabetical ......... 4 Langauages ..................................................... 4 The Environment .......................................... 21 Exported variables .......................................... 21 Common shell variables .................................. 21 Regular Expressions ....................................... 21 Commands & Programs - by Function ............ 5 Archives ........................................................... 5 Communication & Network ............................... 5 Edit & View....................................................... 5 File & Dir Management ..................................... 5 Languages ....................................................... 5 Office Utilities ................................................... 5 Printer .............................................................. 5 Process Management ....................................... 6 Search and Patterns ......................................... 6 System Administration ...................................... 6 Wild Cards ................................................... 22 Wild Strings .................................................... 22 Wild Character ................................................ 22 Match Lists ..................................................... 22 Quoting ........................................................ 23 Single Quotes ................................................. 23 Double Quotes ................................................ 23 Single Character Escape ................................ 23 I/O Redirection ............................................. 24 Output Redirection .......................................... 24 Input Redirection............................................. 25 Here Documents ............................................. 25 Pipes — Connecting Commands .................... 26 Basic Directory Structure ................................ 7 Common Backup Directories ............................ 7 Log files ........................................................... 7 Spool files ........................................................ 7 Configuration files............................................. 8 Device files ....................................................... 8 Other Important files ......................................... 9 X Window files .................................................. 9 Unix Commands........................................... 27 Search Order .................................................. 27 Chmod Command ........................................... 27 Echo ............................................................... 27 Expr ................................................................ 28 False .............................................................. 30 True ................................................................ 30 Go Function .................................................... 30 redo ................................................................ 31 Kill .................................................................. 31 Shutdown ....................................................... 32 Set Command ................................................. 32 Test ................................................................ 33 Trap Command ............................................... 34 Special Characters ....................................... 10 Input/Output .................................................. 10 Preset Shell Parameters ............................... 10 Login environment .......................................... 11 Shell internal settings ..................................... 11 Process ID variables....................................... 12 ksh/bash additional features ........................... 12 Bash Shell Concepts .................................... 13 Syntax ............................................................ 13 Bash Startup & Kill ........................................ 13 Configuration Files ......................................... 13 Invoking Shell ................................................. 14 ‘dot’ Command ............................................... 14 XWindow & KDE Startup ................................ 15 Background Processing .................................. 15 Terminating a Process .................................... 15 Environment ................................................... 15 Conditional Statements ................................ 34 If Statement .................................................... 34 While Statement ............................................. 36 Until Command ............................................... 37 For Command ................................................. 37 Case Command .............................................. 37 Shell Functions............................................. 38 Functions vs. Scripts ....................................... 38 Defining a Function ......................................... 38 Where to Define Functions .............................. 39 Status of Definitions ........................................ 39 Built-in Shell Commands .............................. 17 Parameters & Variables ................................ 18 Assigning a Variable ....................................... 18 Referencing a Variable ................................... 18 Special Variables............................................ 18 Position Parameters ....................................... 19 Shift Command .............................................. 19 Set Command ................................................ 19 Conditional Use of Variables........................... 20 Search Order................................................ 39 Command Line Shell Invoking ...................... 40 Invoking .......................................................... 40 Debugging.................................................... 41 Linux Bash Command Reference Sheet....... 42 NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 3 of 45 May 15, 2012 Copyright © 2002-2012 Commands & Programs - Alphabetical adduser awk at bc cal calendar cancel cat cd chgrp chmod chown cmask cmp comm compress cp cpio cron cu cut date dd df diff du echo emacs env ex eqn find finger fork fsck ftp grep gzip head history info join kill less ln login lp lpc lprm lpstat lpq ls mail mailx man mesg mkdir mm more manage user account search & editing job scheduler calculator calendar reminder service remove print jobs from queue concatenates or prints files change directory change group permissions change file/dir permissions change owner permissions sys def permission – see umask compare two text files find same lines of sorted files compress file copy files file archive program job scheduler call another system cut/paste columns of text date and time file copy program mounted file sys/drives info difference between two files file & dir disk usage shows argument editor show environment variables line-oriented text editor format mathematical text find and act on files user info create child process file system check and fix file transfer search pattern and do action compress files show first lines of file print last commands like man, command info join two columns of text terminate or send signals file viewer create file links sign on to system line printer manager manage print jobs remove print jobs status of print jobs status of print jobs show directory contents manage mail advanced mail management manual of command info permit or deny talk messages create new directory macro print formatter file viewer, use less instead mount mv ping netstat nroff passwd paste pg ping postnews pr ps pstat pwd rcp readnews rlogin rm rn rmdir rpm script sed shl sort spell shutdown split stty tbl tail talk tar tee telnet time troff umask umount uncompress uniq uptime uucp uupick uuto vi wc who write zcat init make file sys or device move or rename files transfer time & route transfer info print formatter, use mm instead change login password cut and paste columns of text file viewer, use less instead transfer time & route netnews writer format and print text file show program status show kernel info print working directory remotely copy files netnews manager remote login remove files netnews manager remove directories manage packages saves bash session to file pattern editor shell manager ort and merge text files spelling checker halt or reboot system text editing set terminal options put tables into documents view last lines of text file talk (type) to another user combine files split output net file manager time info typeset formatting usr default perm – see cmask remove file system or device expand compressed file remove dup lines of text file elapsed time since boot file transfer between systems retrieve file sent via uuto Send file to another system text editor word count who is logged into system write to another user display compressed file Langauages cc f77 make nasm pc perl c compiler fortran compiler source code manager assembler pascal compiler perl compiler NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 4 of 45 May 15, 2012 Copyright © 2002-2012 Commands & Programs - by Function Archives compress cpio gzip rpm tar uncompress zcat compress file file archive program compress files manage packages combine files expand compressed file display compressed file cp dd df du find fsck grep ftp ln ls mkdir mount mv path pwd rm rmdir umount uucp uupick uuto copy files file copy program mounted file sys & drive info file & dir disk usage find and act on files file system check and fix search pat and act on file file transfer create file links show directory contents create new directory make file or dev available move or rename files change shell environment print working directory remove files remove directories remove file system or device file transfer between systems retrieve file sent via uuto Send file to another system Communication & Network cu ftp getty netstat ping pty tty rcp rlogin rset stty talk tee telnet termcap tset uucp uupick uuto call another system net file manager transfer info transfer time & route remotely copy files remote login set terminal options talk (type) to another user split output net file manager Languages cc f77 gcc java make nasm pc perl tk tkl c compiler fortran compiler gcc compiler java compiler source code manager assembler pascal compiler perl compiler tk compiler tkl compiler file transfer between systems retrieve file sent via uuto Send file to another system Edit & View awk cat cmp comm cut diff echo emacs eqn ex head join less more nroff paste pg sed sort split tail tbl uniq vi search, filter, edit concatenates or prints files compare two text files find same lines of sorted files cut & paste columns of text difference between two files show argument(s) editor format mathematical text line-oriented text editor show first lines of file join two columns of text file viewer file viewer, use less instead prt formatter, use mm instead cut and paste columns of text file viewer, use less instead search, filter, edit sort and merge text files txt edit view last lines of text file put tables into documents remove duplicate lines text editor Office Utilities bc cal calendar date mail mailx postnews readnews rn spell talk time wc who write calculator calendar reminder service date and time mail managment advanced mail management netnews writer netnews mgr, use rn instead netnews manager spelling checker talk (type) to another user time info word count who is logged into system write to another user Printer cancel lp lpc lprm lpstat lpq mm nroff pr troff remove print jobs from queue line printer manager manage print jobs remove print jobs status of print jobs status of print jobs macro print formatter prt formatter, use mm instead format and print text file typeset formatting File & Dir Management cd chgrp chmod chown change change change change directory group permissions file/dir permissions owner permissions NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 5 of 45 May 15, 2012 Copyright © 2002-2012 Process Management at cron date env export fork kill ps tee job scheduler job scheduler date and time show environment variables send variable to shell create child process terminate or send signal program status split output Search and Patterns awk find grep sed sort nohup ps tee pattern scanning find and act on files search pat and act on file pattern editor sort and merge text files prog running after logoff program status split output System Administration adduser chgrp chmod chown manage change change change user account group permissions file/dir permissions owner permissions cmask date echo env find finger grep history info login mail mailx man mesg passwd path pstat script shl shutdown stty time umount umask uptime who sys default perm – see umask date and time shows argument show environment variables find and act on files user info search pattern & do actions show command history like man, command info sign on to system manage mail advanced mail management manual of command info permit or deny talk messages change login password change shell environment show kernel info saves bash session to file shell manager halt or reboot system set terminal options time info remove file system or device usr default perm – see cmask elapsed time since boot who is logged into system NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 6 of 45 May 15, 2012 Copyright © 2002-2012 Basic Directory Structure / ................................. /bin ............................... /boot .............................. /dev ............................... /etc ............................... /home .............................. /lib ............................... /lost+found ........................ /mnt ............................... /opt ............................... /proc .............................. /root ............................. /sbin .............................. /tmp ............................... /usr ............................... /usr/bin ........................... /usr/doc ........................... /usr/man ........................... /usr/include ....................... /usr/include/g++ ................... /usr/lib ........................... /usr/local ......................... /usr/sbin .......................... /usr/src ........................... /usr/src/linux ..................... /usr/tmp ........................... /var ............................... /var/tmp ........................... ;root directory ;system commands ;kernel & boot files ;device drivers ;pub system configuration files ;user private files & settings ;c compiler libraries ;files fragments are saved here ;external file systems and devices ;optional programs, i.e. KDE ;process files ;root’s custom files & settings ;superuser commands needed to start ;system temporary files ;pub cmds & prop, can be read-only ;pub commands ;pub info files ;pub man files ;pub c header files ;pub c++ header files ;pub libraries ;extensions independent of distro ;superuser commands ;pub application source files ;kernel source files ;pub temporary files ;config files, link to /usr ;pub temporary files Common Backup Directories /etc/lilo.conf ..................... /boot/grub ......................... /etc/fstab ......................... /etc/modules.conf .................. /etc/isapnp.conf ................... /etc/Xll/XF86Config-4 .............. /etc/X11/XF86Config ................ /etc/cups .......................... /etc/printcap ..................... /etc/bashrc ........................ /etc/profile ....................... /etc/crontab ....................... /etc/rc.d .......................... /etc/inittab ....................... /etc/ssh ........................... /root ............................. /home .............................. ;Lilo’s boot loader configuration ;grub’s boot loader configuration ;disk partition table configuration ;modules to load % their parameters ;ISA Plug & Play hardware parameters ;X’s settings X’s settings ;CUPS’s printer settings ;lpr print settings ;bash shell system-wide configuration ;system-wide environment ;cron jobs to be executed ;run level settings ;sets default run level & settings ;ssh settings for secure remote access ;root’s custom files & settings ;user’s custom files & settings Log files /var/log ;log files Spool files /usr/spool /usr/spool/lp ;buffer for file xfer, etc ;buffer for printer NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 7 of 45 May 15, 2012 Copyright © 2002-2012 Configuration files /boot/grub ......................... /etc/bashrc ........................ /etc/crontab ....................... /etc/cups .......................... /etc/DIR_COLORS .................... /etc/fstab ......................... /etc/group ........................ /etc/hosts ........................ /etc/initd.conf ................... /etc/inittab ....................... /etc/isapnp.conf ................... /etc/lilo.conf ..................... /etc/modules.conf .................. /etc/passwd ....................... /etc/printcap ..................... /etc/profile ....................... /etc/rc.config ..................... /etc/rc.d .......................... /etc/shadow ....................... /etc/ssh ........................... /etc/syslogd.conf ................. /etc/XF86Config .................... /etc/X11/XF86Config ................ ~/home/.profile .................... /sbin/init.d ....................... ;grub’s boot loader configuration ;bash shell system-wide configuration ;cron jobs to be executed ;CUPS’s printer settings ;ls color settings ;disk partition table configuration ;user groups ;hostname to address table ;net services, ftp, telnet, etc ;sets default run level & settings ;ISA Plug & Play hardware parameters ;lilo’s boot loader configuration ;modules to load & their parameters ;usr info, shell pref, home dir, etc ;lpr print settings ;shells login script ;sys config settings read during boot ;run level settings ;passwords ;ssh settings for secure remote access ;syslog daemon settings ;X window settings ;X’s settings ;usr custom environment settings ;scripts for system start Device files /dev/fd0–fd1 ....................... /dev/hda ........................... /dev/hda1–hda15 .................... /dev/hdb ........................... /dev/hdb1–hdb15 .................... /dev/sda ........................... /dev/sda1–sda15 .................... /dev/sdb ........................... /dev/sdb1–sdb15 .................... /dev/sdc... ........................ /dev/cdrom ......................... /dev/hda - hdd ..................... /dev/scd0 – scd1 ................... /dev/rmt0 .......................... /dev/nrmt0 ......................... /dev/ftape ......................... /dev/ntape ......................... /dev/mouse ......................... /dev/atibm ......................... /dev/logibm ........................ /dev/inportbm ...................... /dev/modem ......................... /dev/ttS0–ttS3 ..................... /dev/cua0–cua3 ..................... /dev/lp0–lp2 ....................... /dev/tty1–tty8 ..................... /dev/null .......................... /dev/zero .......................... ;floppy ;1st IDE & CDROM drive ;1st IDE & CDROM drive partitions ;2nd IDE & CDROM drive ;2nd IDE & CDROM drive partitions ;1st SCSI & USB drive ;1st SCSI & USB drive partitions ;2nd SCSI & USB drive ;2nd SCSI & USB drive partitions ;3rd SCSI & USB drive... ;cdrom drive, linked to driver ;ATAPI IDE cdrom drive ;SCSI cdrom drive ;1st SCSI tape, auto rewinds ;1st SCSI tape, no auto rewind ;1st floppy tape, auto rewinds ;1st floppy tape, no auto rewind ;mouse ;ati graphics card mouse ;logitech mouse ;ps/2 bus mouse ;link to com port with modem ;serial port ;serial port ;parallel port ;virtual serial console ;null device ;output endless null bytes NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 8 of 45 May 15, 2012 Copyright © 2002-2012 Other Important files /usr/linux ......................... /etc/skel .......................... /”home”/ ........................... .profle ............................ .bashrc ............................ .exrc .............................. .xinitrc ........................... .fvwmrc ............................ .ctwmrc ............................ .openwin-menu ...................... ;kernel source ;new user skeleton files copied to users user personal and setup files usr login script usr bash config usr vi config usr x win startup fvwm win mgr startup ctwm win mgr startup olvwm win mgr startup X Window files Coming soon ........................ kernel source NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 9 of 45 May 15, 2012 Copyright © 2002-2012 Special Characters | ; & && || ‘ “ \ ? * [chars] [!chars] <upside down pipe — connects two commands command separator run process in background; default stdin from /dev/null only run command if previous command completed successfully only run following command if previous command failed enclose string to be taken literally enclose string to have parameter and cmd substitution only ignore special meaning of following character match single character in filename match 0 or more characters in filename match any of chars (pair separated by a — matches a range) match any except chars comma> in-line command execution Input/Output All of these operators may be preceded by an optional file descriptor. Defaults are shown in parentheses. < file > file >> file <&n >&n <&>&<< word use file as stdin use file as stdout like > but append to file if it exists duplicate input file descriptor from n (stdin) duplicate output file desc. from n (stdout) close stdin close stdout treat line with word as EOF on input If any of word is quoted, no additional processing is done on input by shell. Otherwise: parameter & command substitution occurs escaped newlines are ignored a \ must be used to quote \, $, as above with leading tabs ignored <<- word Preset Shell Parameters Several special variables are used by the system -- you can use these, but may not be able to change them. The special variables use uppercase names, or punctuation characters. Some variables are set by the login process and inherited by the shell (e.g. $USER), while others are used only by the shell. These are some of the more commonly used ones: 1 2 3 $n $* $@ “$*“ “$@“ $# default input default output default error use positional parameter n all positional parameters all positional parameters equivalent to “$1 $2 ...“ equivalent to “$1” “$2”... number of positional parameters There are various ways to conditionally use a variable in a command. ${datafile-default} Substitute the value of $datafile, if it has been defined, otherwise use the string "default". This is an easy way to allow for optional variables, and have sensible defaults if they haven't been set. If datafile was undefined, it remains so. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 10 of 45 May 15, 2012 Copyright © 2002-2012 ${datafile=default} Similar to the above, except if datafile has not been defined, set it to the string "default". ${datafile+default} If variable datafile has been defined, use the string "default", otherwise use null. In this case the actual value $datafile is not used. Substitute the value of $datafile, if it has been defined, otherwise display datafile: error message. This is used for diagnostics when a variable should have been set and there is no sensible default value to use. $name $name: ${var} ${var—text} ${var=text} ${var?text} ${var+text} only checks if name is set checks if name is set and non-NULL use braces to delimit shell variable name use var if set, else use word use var if set, also set name to word use var if set, otherwise print word and exit use word if var set, otherwise use nothing Example ${datafile?"error message"} debug message if var is not set Login environment $EDITOR $USER $LOGNAME $PATH $TERM $PAGER If set, this contains the name of the program which the user prefers to use for text file editing. A program which needs to have the user manually edit a file might choose to start up this program instead of some built-in default (e.g. "crontab -e". This also determines the default command-line-editing behavior in interactive shells. currently logged-in username Preset to the. The list of directories that will be searched for external commands. You can change this in a script to make sure you get the programs you intend, and don't accidentally get other versions which might have been installed. The terminal type in which the shell session is currently. Usually "xterm" or "vt100". Many programs need to know this to figure out what special character sequences to send to achieve special effects. If set, this contains the name of the program which the user prefers to use for text file viewing. Usually set to "more" or "less" or something similar. Many programs which need to present multipage information to the user will respect this setting (e.g. man). This isn't actually used by the shell itself, but shell scripts should honour it if they need to page output to the user. name of default shell search path for cd command home directory for cd command field separators (space, tab. newline) name of a mail file, if any check for mail every n seconds fnames to check new mail (: separator; %message) primary prompt string ($) secondary prompt string (>) accounting file for user shell procedures set name to specified word $SHELL $CDPATH $HOME $IFS $MAIL $MAILCHECK $MAILPATH $PS1 $PS2 $SHACCT name=word fname may be followed by Shell internal settings $PWD Always set the current working directory (readonly) $OLDPWD The previous directory (before the most recent cd command) $? (readonly) Set to the exit status of the last command run, so you can test success or failure. very command resets this so it must be saved immediately if you want to use it later. Pg 11 of 45 May 15, 2012 Copyright © 2002-2012 NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference $$IFS Option flags of current shell command. Internal Field Separators: the set of characters (normally space and tab) which are used to parse a command line into separate arguments. This may be set by the user for special purposes, but things get very confusing if it isn't changed back. Process ID variables (readonly) Set to the process ID of the current shell - useful in making unique temporary files, e.g. /tmp/$0.$$ $PPID (readonly) Set to the process ID of the parent process of this shell - useful for discovering how the script was called. $! (readonly) Process ID of the last command started in background. $$ ksh/bash additional features $SECONDS $RANDOM (readonly) Integer number of seconds since this shell was started. Can be used for timing commands. Every time it is valuated, $RANDOM returns a random integer in the range 0-32k. RANDOM may be set to "seed" the random number generator. $LINENO (readonly) Always evaluates to the current line number of the script being executed - useful for debugging. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 12 of 45 May 15, 2012 Copyright © 2002-2012 Bash Shell Concepts Syntax This section provides a reference for commands built into the shell. Words with-in <> are substitutes for unprintable characters, for example <tab>. <> may also be used for mandatory options, files, or input. Whitespace consists of one or more <spaces> and/or <tab> characters. In addition, commands are terminated by any of the following characters: ; & () ^ <newline> <space> <tab>. Boldface represents words typed exactly as they appear. Italics represent words to be substituted for things such as filenames. Note that if an italicized word is plural (i.e. files), multiple arguments are permitted. A digit at the end of a word such as var1 indicates a unique name so it can be referenced in the description. The following substitutable words are used in this reference: file — list — n — name — oct — pat — word — or fname: a filename, pathname, or variable of one one or more pipelines that can be separated by ;, &, &&, || and optionally be terminated by ; or &. an integer the name of a shell variable an octal number explained in conjunction with the case command. a generic argument; a word. Quoting may be necessary if it contains special characters. Bash Startup & Kill Configuration Files The /etc/profile is the main startup file for all bash shells. It usually looks in the user’s home directory for further instructions. The home directory should contain one or more of the following bash startup files, which contain commands that apply only to the current user's bash session: $HOME/.bash_profile $HOME/.bash_login $HOME/profile $HOME/.bash_rc $HOME/.bash_logout To understand how bash uses startup files, consider the difference between a login shell and a non-login shell. A login shell is created when a user enters the operating environment using a name and password account. A non-login shell is created when an additional bash shell is launched within the user session, as you do when you open a terminal window in X, or execute a shell program. To starta shell, bash consults the following files in the specified order: Login Shell /etc/profile $HOME/.bash_profile usually points to -> $HOME/.bash_login $HOME/profile Non-Login Shell 1. $HOME/bash.rc 1. 2. 3. 4. When you start a non-login shell, bash consults only one startup file, Because login and non-login shells use different startup files, the shells created may differ. Most Linux distributions contain an automatically generated NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 13 of 45 May 15, 2012 Copyright © 2002-2012 ~./bash_profile that contains a script that automatically executes the commands placed in ~/bash_rc. This script ensures that the login shell will be configured like the non-login shell. To add a command that is automatically executed when any user begins a login shell, add the command to /etc/profile. You'll need to switch to superuser status to edit this file. To add a command that is executed when you start a login shell in your own user account, use ~/bash.profile for commands that must be executed before commands contained in ~/.bash_login or ~/profile. Use ~/profile for commands that must be executed only after the shell executes the commands found in ~/.bash.profile and ~/bash_login. To add a command that is executed when you start a non-login shell, use ~/.bashrc. Invoking Shell This section shows the syntax for invocation of the shell. In order to parse the command line properly, the arguments must be separated in a manner the shell understands. Whitespace and/or punctuation is used. Whitespace consists of one or more space characters, tab characters, and/or the end of line character. Punctuation consists of the characters () ; | <> >> The end of a command line is generally signified by entering the newline character, usually represented by the <RETURN> key. You can also separate commands with a semicolon (;). The pound sign (#) character indicates the beginning of a comment to the shell. All characters from the # to the end of the line are ignored. sh [options] [args] Options: —a mark modified export variables —c cmd execute cmd, default reads cmds from file in first entry of args. —e if non-interactive, exit if a command fails —f disable wildcarding —h locate and remember functions on definition instead of on execution —i set interactive mode —k all keyword arguments placed in environment —n read commands without executing them —r set restricted mode —s read commands from stdin —t read and execute one command, then exit —u set error upon substituting an unset variable —v print input lines as read —x print commands and arguments as executed All options except c, i, r, s can be set or unset within the shell with the set command. ‘dot’ Command The shell has a built-in command represented by a period . which is pronounced dot. This command reads a file of commands without creating a sub-shell. This means you can change our environment by interpreting a file with the dot command. For example. if you modified your .profile you could re-interpret it without having to log back in by entering: . .profile If you create various files to set up different environments for yourself, you will probably want to set different values for PSI so you know which environment you are in. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 14 of 45 May 15, 2012 Copyright © 2002-2012 XWindow & KDE Startup For completeness the xwin startup is briefly discussed here. The xwindow system should always be started using the startx command which is designed to get things going. A tremendous amount of programs and synchronization is needed for the GUI to successfully load. startx <- shell command calls xinit command which must have things setup for it xinit shell command calls the following config files in order $HOME/.Xresources <- usually exist $HOME/.Xmodmap <- usually exist $HOME/.xinit <- does not usually exist $HOME/.Xclients <- does not usually exist /etc/X11/xinit/xinitrc /etc/X11/xinit/Xclients KDE users have a nice directory (folder) where the entire contents will be run, this is similar to MS Window’s startup folder. $HOME/.kde/Autostart Background Processing Instead of running a command interactively, it can be run in the background. This means that the command will continue to run but you will immediately get your prompt back so that you can continue with interactive use of your terminal. To start a command in the background. append an ampersand & to the end of the command line. You may want to redirect the output so that it doesn’t interfere with what you are doing. For example, to find all the tiles named .core in the /usr directory and save their names in a file, use the command... find /u -name .core -print > temp & Find would run and you could check to see if it was complete by using the ps command. The file temp would grow as it received output from the command. When a command is started in the background, the shell establishes a slightly different environment for it. The stdin of the command is connected to /dev/null instead of /dev/tty. This means that if the command reads any input from standard input, it will get an end of file (EOF). Also, the interrupt and quit signals are disabled. This means that if you interrupt an interactive program while you have a background job running, the background job will not be affected. The hangup signal, however, is sent to the job. If you intend to have your background job continue even if you log out, you should precede the command with the nohup command. This tells the shell not to send the hangup signal to the command. For example, to run find as described above and have it ignore the hangup signal... nohup find /u -name .core -print > temp & Terminating a Process The kill command can be use to terminate any process. It can send any one of many different signals. Don’t confuse the kill process command with the computer shutdown commands. halt poweroff reboot shutdown Environment When you first login many defaults are setup. Two examples are your home directory $HOME and a default search path $PATH for commands. It is possible to alter these defaults by creating a file called .profile in your home directory and placing the NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 15 of 45 commands to alter your environment in this file. Whenever you log in, the shell interprets this file. If you set a shell variable and want it to be exported subsequent shells will receive its value, you must put You may also want to define some shell functions as used commands and place them in .profile. The following export PATH TERM CDPATH PATH=$HOME/bin:/bin:/usr/bin:. CDPATH=:$HQME:/usr/local PS1=”Hi Phil >“ TERM=h19 umask 027 news –n to the environment so that it in an export statement. abbreviations for commonly is a sample .profile The first line establishes three variables to be exported to the environment. Next, the variable PATH is set to a string of directory names. Each name is separated by a colon :. This establishes where the shell will search for commands. In this example, it first searches sub-directory bin of your home (login) directory, then /bin, then /usr/bin, and finally the current directory represented by a dot. CDPATH establishes where the cd command looks for a directory that does not contain a leading slash. By default, it would look in your current directory. By assigning a new value to CDPATH, the cd command would first look in the current directory (identified by the: immediately following the =, then look in your home directory, and finally /usr/local. PS1 establishes your primary prompt string. This string will appear instead of the default % as the shell prompt. The TERM variable is used to establish the terminal type you use. If you do not always use the same type of terminal, this line can contain a reference to the test command to conditionally establish terminal type. The umask command sets the file creation mask which is used to limit the access capabilities of any files that you create. This particular value (027) establishes the maximum access permissions as anything for owner, read and execute for group and nothing for other. The -n option is to print out any news items that are current and then update the time stamp file that it uses to keep track of what you have read. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 16 of 45 May 15, 2012 Copyright © 2002-2012 Built-in Shell Commands start of comment: terminated by a newline read and execute commands from file null command: returns 0 exit status see test exit from enclosing for or while loop change current directory to file do next iteration of enclosing for or while echo words (see echo in Appx. B) evaluate words and execute result execute words in place of shell exit with return value n export names to environment of commands parse parameters and options remember locations of files; with no files shows hash info —r forgets all remembered locations newgrp [words] same as exec newgrp words pwd print working directory name read names read stdin and assign to names readonly [names] mark names read-only; print list if no names, return n, exit with return value n with no n return status of last command set [—options] [words] set flags (aefhkntuvx- are valid). words set positional parameters set [+options] [words] unset flags shift [n] rename positional parameters; $n+1 =$1... (n defaults to 1) test evaluate conditional expressions times print accumulated process times trap [word][sigs] execute word if signal in sigs received no word or sigs — print traps no word — reset sigs to entry defaults word is null string — ignore sigs sigs is 0 — execute word on exit from shell type files show how shell would interpret each file ulimit [options] [n] limit size to n (if no n. print current limits) —f files created by child processes (n blocks default) —p change pipe size to n umask [oct] set file creation permissions mask (see chmod) unset [names] unset variables or functions names wait [n] wait for process n; if no n, wait for all children # .file : [ break [n] cd [file] continue [n] echo [words] eval [words] exit [words] exit [n] export [names] getopts hash [—r] [files] NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 17 of 45 May 15, 2012 Copyright © 2002-2012 Parameters & Variables Shell variables can be used to remember values that you intend to use later. Shell variable names can be made up of letters a-z A-Z and the underscore _ character. There are no data types in the shell. All shell variables are character strings. These shell variables are built-in, named save areas that you can create by referencing them by name. You can perform arithmetic functions on shell variables using the expr command. Assigning a Variable In order to assign a string to a variable you enter what looks like an algebraic expression. Note that there must be no spaces around the equals = character. For example, to assign the string joe to the shell variable worker... worker=joe If the variable contains any special characters, including whitespace, you need to quote it. For example... worker=”joe smith” The double quotes do not become part of the string, they just prevent the interpretation of the special meaning of the space character in the assignment statement. Referencing a Variable To reference a shell variable, precede its name by the dollar sign $ character. For example, meal=”steak ” echo $salad ;would show: steak If you need to insert a variable reference with other characters, you can use braces {} to delimit the variable name. echo Eat ${meal}and milk. ;would show Eat steak and milk. Whereas... echo Eat $mealand milk. would attempt to reference a shell variable $mealand that does not exist. You can also assign command names to shell variables. For example, cmd=ps option=-ef $cmd $option ;performs command ps -ef Special Variables There are built in variables too. For example, $PS1 is your primary shell prompt string (usually %). Another example is $$, the process number of the current shell. This is commonly used to create unique filenames. The following statement would be a good way to create a unique filename. It could then be referenced by a reference to the shell variable z. z might equel something like xyz8423. z=xyz$$ Another special variable is $? which contains the exit status for the last command executed. $? is set to 0 if the command executed successfully, non-0 otherwise. Commands return a different non-zero exit status depending on the type of failure. You can look at values of individual variables by referencing the variable in an echo command. For example, the following command displays the values of the HOME and TER\1 shell variables: echo $HOME $TERM NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 18 of 45 May 15, 2012 Copyright © 2002-2012 The set command displays the values of all shell variables (and shell functions). Position Parameters When you start a shell script you can pass parameters to it. For example, you may need to pass a file name. These parameters are placed on the invocation line following the command and are called positional parameters. These parameters are referenced in the same manner as shell variables. Description Variable --------------------------------------------number of positional parameters $# command name that invoked script $0 1st parameter $1 2nd parameter $2 etc... For example, the following command... ls –l * Would have the following parameters, Description Variable Value ------------------------------------------------------------------number of positional parameters $# 2 command name that invoked script $0 ls 1st parameter $1 -l 2nd parameter $2 * etc... Parameters can also be passed by name by preceding the command that invokes the shell script with assignments to variables. For example, the following command will invoke the shell program cool with shell variable first set to 5 and shell variable last set to 10. first=5 last=10 cool These assignments do not affect the variables in the current shell. They are merely named passed parameters, commonly called keyword parameters. Shift Command Shift deletes the first positional parameter $1 and shifts each subsequent parameter one place to the left. In other words, $2 becomes $1, $3 becomes $2 and so forth. Set Command The • • • set command allows you to do three things: set shell options change positional parameters display set variables The shell, like most UNIX commands, has options which may appear on the command line. Unlike other commands, many of these options can be changed by the use of the set command. The positional parameters ($1. $2. ) can be changed using set. For example, to set the first three positional parameters ($1, $2, and $3, to uno, dose, trace, you would use the following set command... set uno dose trace After this command, the command NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 19 of 45 echo $2 for example, would print dose Finally, set with no options prints a list of all shell variables (and functions) that are currently defined. Conditional Use of Variables Sometimes it is desirable to be able to conditionally use values of a shell variable. For example, if a variable is missing it may be desirable to insert a default value. This can be done by an extension of the variable reference notation using braces. The expression ${var} is a reference to the value of the shell variable var. The following additional forms are available. Note that without the : in the expression, the variable is only checked to see if it is set; whether or not the variable is non-null is not considered. ${var:-word} ${var:=word} Substitute value of var if set and non-null; otherwise substitute word. If variable is not set or is null, set it to word. Then use value of var. Note that this cannot be used to assign values to positional parameters. Use value of var if set and non-null. Otherwise, print word and exit from the shell, If word is omitted, parameter null or not set is printed. If var is set and non-null, word is substituted, Otherwise nothing is substituted. ${var:?word} ${var:+word} The following version of append will append to the file /tmp/app.data if you do not specify a file name on the invocation line. In other words, if $1 is not set, the file /tmp/app.data is used. # append version 1 echo “control-D to terminate” cat >> ${l:-/tmp/app.data} The following version of append complains when it is invoked without a filename on the command line. # append version 2 echo “control—D to terminate:” cat >>${l:?”filename required”) This version prints out the message append: 1: filename required if you enter the command with no parameters. Unfortunately. the error message is printed out after the information message from echo. Version 4 gets around this problem by assigning the parameter to a shell variable named fn which Is then used in the cat command if the substitute doesn’t tail. # append version 3 fn=${1:?”filename required”} echo “control—D to terminate:” cat >>$fn NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 20 of 45 May 15, 2012 Copyright © 2002-2012 The Environment The environment consists of pairs of names and values. When a shell is started (either from logging into the shell or from starting a sub-shell) the shell scans the environment and creates a variable with the related value for each pair found. Exported variables When a one program invokes another program, the child program receives all of the exported environment variables of the parent. By default, environment variables are not exported. Shell variables can be bound to the environment by use of the export command. If a variable is named in an export statement, any future shells will inherit this new variable and its associated value. Note, however, that you cannot pass information back to a calling shell through this mechanism. Common shell variables Most shells have the following set: variable DISPLAY EDITOR HOME PAGER PWD SHELL TERM USER description tells X11 on which display to open windows default text editor; usually emacs or vim path to user's home directory; same as ~ default page-scroller to use; usually less current directory; same as output of pwd path to the current shell current terminal type account name of current user The statement export with no arguments will display all variables that are currently being exported. One of these, $HOME, is the pathname of your login directory, is initially extracted at login time from your password file entry. For example, the new version of append looks in the environment for a variable named afile to determine what file to append to if none is specified on the command line. # append version 4 fn=${1:—${afile:?”filename req’d”}} echo “appending to $fn” echo “control-D to terminate:” cat >> $fn Regular Expressions Note: multiple re’s may be concatenated c the character c \c character c (for special characters) . any character except a newline [str] any one character in str ([a-b] means all in range a thru b) NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 21 of 45 [^str] re* re\{m,n\} \(re\) \n ^ $ <null> & % any character except newline or one from str 0 or more occurrences of 1 character re m thru n occurrences of 1 character re group re for later reference nth re in\(..\) beginning of line (not in expr) end of line default re — last re encountered put matched string in replacement same as last replacement Wild Cards Wild Strings The asterisk * matches any number of characters. In other words, 0 or more of any characters. For example, if you wanted a long list of the characteristics of all files in the current directory whose names contained the string test. you could use the following command: ls —l *sample* The first * means that there can be 0 or more characters before the literal string “sample” and the second * means there can be 0 or more after the string. Therefore, files with names like sample01, xsample, and ysample33.db will all be listed. Wild Character Single character made with the question mark ?. For example, a long listing of all files whose names begin with z and are exactly three characters long would be printed by the command... ls –l z?? Match Lists A third kind of wildcard is a match list. The syntax is [list] here list is the list of characters to be matched. For example, the following echo command will show all the file names whose first letter is a, second letter is b or c, and third letter is d. ls –l a[bc]d A range can be specified by using a dash, so the following would match files whose names begin with w, second letter is h,I,j,k, third n, and forth x,y, or z. ls –l w[h-knx-z] The three kinds of wildcards can be combined to perform matches. For example. the following command would echo all file names whose third letter is x,y, or z. echo ??[x-z] The exclamation ! character can be used to reverse a comparison. It must appear as the first character inside the brackets. For example, the following command would produce a long list of all files whose names do not start with a lower case letter: ls —l [!a-z]* Testing Wildcards The use of wildcards can be dangerous. It is very easy to inadvertently remove the wrong files by using the rm command in conjunction with wildcards. If you are not sure what files will be effected, you can use the echo command to test the pattern. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 22 of 45 May 15, 2012 Copyright © 2002-2012 Quoting It is necessary to quote strings in order to prevent the shell from treating various characters as special. You may need to quote a string to prevent the shell from erroneously interpreting the special meaning of characters such as * or?. Single Quotes The apostrophe or single quote ‘ is used to indicate that all characters in the enclosed string are to be taken literally. For example, echo ‘*[xyz]??’ would echo the string *[xvz]?? rather than any matched file names. Double Quotes The double quote “ tells the shell to interpret only the special characters, dollar sign $, and the backquote `. The special meaning of other characters is not interpreted within double quotes. Single Character Escape The special meaning of a single character can be escaped by preceding it with a backslash \. echo can\’t will print can’t. Double quotes could have been used here but there will be times when the escape character will be the only answer. echo “don’t” The backslash also prevents the interpretation of the newline character. This means that you can continue a command line by entering a \ before the new line and then continue typing on the next line. See the Difference? The following statements illustrate the difference between quotes... # assign * asterisk to variable “xy”. echo ‘$xy’ ;prints $xy echo “$xy” ;prints * echo $xy ;prints <all files> echo \$xy ;prints $xy 1) The first example prints $xy because the $ is protected from interpretation of its special meaning. 2) In the second line, echo prints *, the value of the shell variable me is an asterisk. 3) The third echo lists all files. The shell first substitutes $xy to it’s value the re-scans the line. It is as if you had typed echo *. 4) And the last statement uses the escape character \ to force the $ to be interpreted as a regular character. Therefore, $xy is shown. Backquote The backquote (grave accent) ` tells the shell to treat the enclosed string as a command. The command is executed and the resulting string (output from the command) is substituted in the command line. One use is to assign values to shell variables. echo `date` NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 23 of 45 May 15, 2012 Copyright © 2002-2012 I/O Redirection Note that in redirection, no filename expansion takes place. Therefore, occurrence of shell meta characters such as * or ? is treated literally. any There are three file descriptors which are normally connected to your terminal. Redirection is the process of changing the connections from your terminal to a file or a program. The three file descriptors are... Name descriptor description --------------------------------------------------------------------stdin 0 standard, default input stdout 1 standard output, default output stderr 2 standard error, default error messages Output Redirection Both stdout and stderr can be redirected to a file. To create (or truncate) a file and send standard output to a file, the > operator is used. For example. to send the standard output of the date command to file named sample, use the following command: date > sample Note: Using > causes a file with that name to be created and input sent to it. If the file already exists, it will be erased and only the new information will be added. To create a new file if none exists and add to the end of an existing file, use >>. Therefore, running date > twice will erase the first date. date > sample date > sample Now, running date >> will continue to add each date line to the end of the file. The >> will save both commands output. date >> sample date >> sample Note that since both the > and >> operators are punctuation, you do not need to include spaces around them. The following three command lines are interpreted identically: PS —ef >stats PS —ef > stats ps —ef>stats To redirect standard error you use the same operators but precede them by the file descriptor number (in this case 2) of standard error. For example, to run cc on the file test.c and send errors to a file, you could use the following command... cc test.c 2 > error.log Because the redirection commands are interpreted by the shell, they are never seen by the actual program that invokes it. Thus, where the redirection appears in the command line is unimportant. The following command would be equivalent to the one above... cc 2 > error.log test.c The operator >& can be used to duplicate an existing file descriptor. This basically means that the two output streams are merged. For example, if you wanted to run the pr command on files datal, data2, and data3 and merge the output and error outputs into file all.log, you could use the following command... pr data[123] > all.log 2>&l NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 24 of 45 May 15, 2012 Copyright © 2002-2012 This command says to redirect standard output to the file all.log and create file descriptor 2 by making a copy of file descriptor 1, the descriptor number for stdout. It you want to redirect stdout or stderr for multiple commands, you can use the exec built-in function with redirection. The redirection will remain in effect until another exec command with redirection is given. Note that /dev/tty is a filename for your terminal. You can always use it to send output directly to the terminal or redirect output back to the terminal. For example, the following set of commands on your current stdout, sends the output of the ps and who commands to the file “myout”, to the terminal, sends the output of date to my out and finally resets the standard output back to the terminal: echo “1,2,3 test” ;prints stdout message “1,2,3 test” exec > myout ;change stdout to a file ps ;commands now sent to file “myout” who echo “temporary redirect” > /dev/tty ;echo “temporary redirect” date ;date is sent to file “myout” exec >/dev/tty ;stdout set back to terminal echo “back to normal” ;echo now goes to terminal The operator >&- will close standard output. Like all the other operators in this section, preceding it with a file descriptor number (i.e. 2 for stderr) causes it to refer to a different file descriptor. If you are running a command and want to discard its output you can redirect it to the special file /dev/null. This is bit heaven ☺, the output is sent, never to be seen again. Input Redirection Many commands will read input from either a file named on the command line or from stdin. The wc command is a good example. The two command lines below do basically the same thing. The difference is that in the first line, the wc program is actually opening and reading the file /etc/passwd, whereas the second example has the shell redirect stdout input from the file /etc/passwd before the wc program is executed. wc /etc/passwd wc </etc/passwd To specify a command is to read input from a file, use the < operator. For example, to specify that the command batch (run commands as load permits) should read its input from the file nightly, enter... batch < nightly Here Documents A second form of input redirection, called a here document, tells the shell that input follows the current line. This is used in shell scripts where a command needs to read input up to an end of file (EOF). You can embed your input in the command file using this capability. Here documents use the << operator and a word that indicates how to tell when the end of the input for the command is reached. In the following example, the cat command will display the message “Hello there! How are you?”, on two lines of stdout. The words “mama cries” is used as the indicator. It is defined by its appearance after the <<operator and when it is encountered on a line by itself (after How are you?) the end-of-file status is returned to the cat command. cat <<mama cries Hello there! NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 25 of 45 May 15, 2012 Copyright © 2002-2012 How are you? mama cries Note that both parameter and command substitution are performed on the EOF indicator word. Once performed, a literal comparison is performed to find the matching word. Normally, parameter and command substitution are performed on the input, so it is necessary to use the backslash \ to escape the special meaning of \, $, and ‘. If, however, you quote any part of the EOF indicator word, shell processing of the input is turned off. The following script sends the message exactly as it appears with no parameter substitution, to user joe using the mail command. mail joe <<’EndEOF’ Hi joe. You owe me $4.50 for lunch. Remember our ‘date’? EndEOF Without the quotes around EndEOF, the $ would be treated as a reference to a shell parameter and the ‘date’ would cause the date command to be executed and the result would replace the string ‘date’. A hyphen - can optionally be appended to the << operator. If it is, leading tab characters are stripped from both the EOF indicator word and the subsequent lines of shell input. Pipes — Connecting Commands A command that reads stdin and writes stdout is called a filter. Filters can be connected to other commands using the pipe it’s symbal is |. Note that the command doesn’t have to use both stdin and stdout. In redirection, you are using a file as either a source (stdin) or an output (stdout and stderr). Connections are not limited to two programs. You could use the following sequence to list file names in 5 columns and page them on the screen: ls | pr —5 | pg Also, pipes and redirection can be combined in the same command line. For example, to perform the same function as above but send the output to a file... ls | pr —5 > tmp.file NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 26 of 45 May 15, 2012 Copyright © 2002-2012 Unix Commands Some commands, although not part of the shell, are necessary to do useful work with the shell. The main difference to the user is that these commands will take slightly longer to execute because they must be loaded from the file system. In fact, some commands started out as separate programs and were later added to the shell to speed execution, test is an example of such a command. Search Order When you enter a command, the shell first checks to see if it is one of the commands built into the shell. Second, it checks to see if it is a shell function. If the command isn’t a built-in or a shell function, the shell searches the directories listed in sour PATH shell variable in the order listed to try” to locate the command. This means that shell functions override commands that are stored in files but built-in commands always override shell functions. The type command, a shell built-in command, can be used to determine where the shell will locate a command. Just enter type followed by the command name and the shell will display where it located the command. Chmod Command chmod <mode> <files> ;change permissions of a file or directory mode can be numeric or symbolic. The symbolic case consists of the form [agou][+—=][rstwx] where: a all – default (group, other, user) g group access permissions o other access permissions u user access permissions + add the permission to status of files — remove the permission from status of files = set the permission of files to specified value r read permission s set owner-ID or group-ID on execution save text mode w write permission x execute permission Multiple symbolic modes separated by commas The numeric case is formed from the following columns: 4000 set user ID on execution 2000 set group ID on execution 1000 set sticky bit (leave program in memory as long as possible) 0X00 owner permission, X added 04 (read), 02 (write), 01 (execute) 00X0 group permission, X added 04 (read), 02 (write), 01 (execute) 000X other permission, X added 04 (read), 02 (write), 01 (execute) example: 0744 owner=read, write, execute group&other=read only 0660 owner and group may read or write Echo echo [message] ;echo message to stdout Note: special escape conventions (place string in quotes) \b backspace \c print line without newline form feed \n newline \n octal val (8 bits), n must start w/ 0 carriage ret NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 27 of 45 \t \\ tab backslash Expr expr args ;evaluate expression Arguments must be separated by blanks, are evaluated as follows. A \ indicates that the following character must be escaped: expr1 \| expr2 returns expr1 if neither null nor 0; else expr2 expr1 \& expr2 returns expr1 if neither expr is null or 0; 0 otherwise expr1 cmpop expr2 returns result of integer compare if both args are ints; otherwise, returns result of lexical compare cmpop is: = equal \> greater than >= greater or equal \< less than \<= less or equal != not equal expr1 mathop expr2 returns result of integer arithmetic on expr mathop is: + addition subtraction * multiplication / division % remainder expr: re compare expr with regular expression re search always anchored to beginning of line (^ not special) returns number of chars matched (0 = fail) \(...\) can be used to return portion of expr The eval command is used to force the shell to rescan a command line and execute the result. If you have constructed a command line from shell variables and passed parameters. it may be necessary to rescan it in order to get the intended meaning. Another way of understanding the action of eval is to consider what the shell would do with your command line after substitution took place. For example, if one of the substituted values had the $ character in it, the shell would interpret this as a reference to a shell variable and it would attempt a substitution. This capability of eval allows you the equivalent of indirect addressing. using the contents of a variable as the address of data rather than the actual data. In the following example, the script etest, the string $data is assigned to shell variable ptr. The single quotes are necessary to prevent the interpretation of the $. Next, the string this is it is assigned to shell variable data. The first two echo commands display the values of ptr and data to verify the assertions above. Finally the eval command line evaluates all its arguments and prints the result, This means that $ptr is interpreted and is replaced by its value $data. Then the echo command embedded in the eval command is executed. After the rescan, this echo becomes echo $data and the printed result is this is it. * etest ptr=’ $data’ data=”:his is it’ echo ptr is .$ptr. echo data is .$data. eval echo $ptr Unix shell variables contain character strings. The shell itself has no concept of arithmetic operations. For example, the following command sequence x=5 x=$x+$x echo $x NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 28 of 45 will print out 5+5, not the value 10 that you might have expected. This is where the expr command comes in. expr treats its arguments as operators and operands and performs arithmetic and comparison operations on them. There are two catches: integer (not floating point) arithmetic is performed and each operator and each operand must be passed to expr as a separate argument. Here are some simple examples: expr 5 + 3 prints out 8. expr 12 / 3 + 9 prints out 13, unfortunately, expr 5 * 3 prints out expr: syntax error. This is because the shell expands the * into a list of filenames in your current directory. Escaping the *, either with a backslash or quotes, will solve the problem as in any of the following: expr5\*3 #use\ expr 5 '*/ 3 # or expr 5 "*" 3 # or Note, however, that you cannot just put quotes around the complete expression as in “5 * 3”. This would cause the shell to pass the whole expression as one argument. expr would just print out the string rather than evaluate it. Expanding on this idea, shell variables can be inserted into expressions and we have shell arithmetic. For example, expr $count + 1 would print out the value of shell variable count plus 1. By using backquotes we can get the shell to execute the expr command and assign the result to a shell variable. Thus, we can increment shell variables. count=’expr $count + 1’ Using this capability it is easy to write a primitive version of the pg utility. In this version, standard input is read and output pauses every 20 lines. It is restarted by entering a return. # dumb_pg count=0 while line do count=’expr $count + 1’ if [ $count —eq 20 ] ; then read stuff </dev/tty count=0 fi done The shell variable count is initialized to 0. Then a while loop is executed. The loop continues until the command line returns a false exit status, line is a command that copies a line from standard input to standard output. line returns true unless an end of file is encountered. Therefore, the while loop will execute as long as there is input to read. Shell variable count is incremented and then tested to see if it is equal to 20. If it is, a read is executed that will cause execution of the script to stop until something is entered. The argument to read (stuff) is required. Whatever is entered is assigned to stuff but it is never referenced. count is also reset to 0 and the sequence starts over. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 29 of 45 May 15, 2012 Copyright © 2002-2012 A complete list of all the operators for expr as well as a definition of regular expressions is given in Appendix B. One interesting operator for string operations is the colon (:). It is used to match characters in the first operand against a regular expression specified in the second operand. The only difference between the regular expressions used by ed and those used by expr is that expr anchors all searches to the beginning of the string. This means that “ is not a special character with expr. The : operator of expr normally returns the number of characters successfully matched; 0 if no characters match. Using this return value and the general match anything pattern. .*. the following shell script will return the number of characters in a string: #len — length of a string expr “$1,’ : “ . * One final note. expr receives arguments after they have been processed by the shell. Therefore, if a shell variable contains a string that looks like one of expr’s operators. expr ill become confused. For example, the following would confuse expr: x= expr $x = ‘=‘ This is because, after shell substitution, the command to expr looks like expr = = = The solution is to precede the operands with some character that does not have a special meaning. For example. expr Z$x = Z= will form the same comparison as the earlier example but will not fail because of the special meaning of the = character. False false ;Return unsuccessful Exit Status True true ;Return successful Exit Status Go Function The following shell function is a replacement for the cd command. By using go instead of cd your prompt string will be set to the last part of the pathname of your current directory. go() cd $1 PS1= ‘pwd’ PS1=”’basenarne $PS1` > You use it just like cd. For example. to change to directory /usr/me/junk von enter go /usr/me/ junk Your prompt would then be set to junk>. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 30 of 45 May 15, 2012 Copyright © 2002-2012 redo The following shell function will repeat the specified command forever at the specified interval. Useful for running, a process status every 10 minutes. It clears the screen before each execution. redo () { clscr=’tput clear’ wtime=$l save wait time shift # shift out wait time while true # do forever do echo $clscr clear screen $* # execute command sleep $wtime done The parameters to redo are the W ait time and the command line to execute repeatedly. For example. to run a ps -ef command every 10 minutes (6(X) seconds), enter: redo 600 ps -ef Assigning the output from the tput command to clscr means that it only needs to be executed once. The wait time is assigned to the shell variable wtime and then it is shifted out of the command line. Finally. a while loop is executed which echoes the clear string. executes the command line (referenced by $* and sleeps for the specified time. Kill kill [option] pids option: ;Terminate or send Signal to processes —signo decimal number of signal sent (15 default) 1 hangup 2 interrupt 3 quit 4 illegal instruction 5 trace trap 6 IOT instruction 7 EMT instruction 8 floating point exception 9 kill 10 bus error 11 segmentation violation 12 bad system call argument 13 write on unread pipe 14 alarm clock 15 software termination signal 16 user defined signal 1 17 user defined signal 2 Standard BSD signals . Description Default Hangup Interrupt Quit Illegal instruction Trace trap lOT trap Terminate Terminate Terminate Terminate Terminate Terminate Pg 31 of 45 Numb er Symbolic Name 1 2 3 4 5 6 SIGHUP SIGINT SIGQUIT SIGILL SIGTRAP SIGIOT Can Can Dump Be Be s Caug Blocke Core ht d Yes Yes No Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes May 15, 2012 Copyright © 2002-2012 NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 pids SIGEMT SIGFPE SIGKILL SIGBCS SIGSEGV SIGSYS SIGPIPE SIGALRM SIGTERM SIGURG SIGSTOP SIGTSTP SIGCONT SIGCHLD SIGTTIN SIGTTOU SIGIO SIGXCPU SIGXFSZ SIGVTALR M SIGPROF SIG WINCH SIGLOST SIGUSR1 SIGUSR2 EMT trap Arithmetic exception Kill Bus error Segmentation violation Bad argument to system call Write on a pipe with no reader Alarm clock Software termination signal Urgent socket condition Stop Keyboard stop signal Continue after stop Child status has changed Background read from control terminal Background write to control terminal 10 is possible on a descriptor CPU time limit exceeded File size limit exceeded Virtual time alarm Profiling timer alarm Window changed Resource lost First user defined signal Second user defined signal Terminate Terminate Terminate Terminate Terminate Terminate Terminate Terminate Terminate Ignore Stop Stop Ignore Ignore Stop Stop Ignore Terminate Terminate Terminate Terminate Ignore Terminate Terminate Terminate Yes Yes No Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes No Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes No No No No No No No No No No No No No No No No Yes No No process id number(s) to receive the signal 0 implies all processes resulting from current login) Shutdown shutdown <mode> <time> [message] Example -h = halt, now = time Shutdown –h now Other options inclued –r = reboot, -k = kidding (sends kill message but does not shutdown) Set Command srcfile=dataset1 Creates (if it didn't exist) a variable named "srcfile" and sets it to the value "dataset1". If the variable already existed, it is overwritten. Variables are treated as text strings, unless the context implies a numeric interpretation. You can make a variable always be treated as a number. Note there must be no spaces around the "=". It is possible to export a variable just for the duration of a single command using the syntax: var=value command args set Display all unset srcfile srcfile= NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 the variables currently set in the shell Remove the variable "srcfile" Pg 32 of 45 Give the variable a null value, (not the same as removing it). export srcfile Added srcfile to the list of variables which will be made available to external program through the environment. If you don't do this, the variable is local to this shell instance. export List all the variables currently being exported - this is the environment which will be passed to external programs. To set a variable option, enter the set command followed by the desired option or options. For example. to set x and v. enter: set -xv Unsetting options is similar, except on replace the -with a +. For example, to unset the u and y options. enter: set +uv Because the set command can be embedded in a script as well as entered from the command line. various options can be turned on and off for part of a script. For example, if you are having trouble with a shell script, you could add a set -x command after all of the commands in the script that you know execute properly. Then you would only get debugging information for the part of the script w here the error was occurring. The -f option of set can be used to turn off filename expansion (wildcard interpretation). The following example implements a simple calculator as a shell script using expr: # math set -f echo “math: enter: num op num" echo "op is --, —, *, / or %“ echo “ math > \c” read numi op num2 echo “$numl $op $num2 = \c” expr $num1 $op $num2 It is saved in a file called math. To use. you enter math and it prompts for the operator and two operands. It then uses expr to compute and print the result. If we entered this script without the set -f command. it would work fine until we entered an expression involving multiplication (the * operator. The * would be expanded into the list of filenames in the current directory. By setting -f this expansion is turned off and the script ill work for all operators that are accepted by expr. If you need to determine which flags are set, they are saved in the - shell variable. The command: echo $will display all the set flags. Test test expression Expressions: —b file —c file —d file —f file ;evaluate expression true true true true if if if if file file file file exists exists exists exists and and and and is is is is a a a a block special file character special file directory regular file May 15, 2012 Copyright © 2002-2012 NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 33 of 45 —g file —k file —n string n1 —eq n2 n1 —ge n2 n1 —gt n2 n1 —le n2 n1 —lt n2 n1 —ne n2 —p file —r file —s file string s1 = s2 s1 != s2 —t [fd] —u file —w file —x file —z string true true true true true true true true true true true true true true true true true true true true if if if if if if if if if if if if if if if if if if if if file exists and has set-GID bit set file exists and has sticky bit set string is of non-zero length integers n1 and n2equal integer n1 >= and n2 integer n1 > n2 integer n1 <= n2 integer n1 < n2 integers n1 and n2 unequal file exists and is a named pipe file exists and is readable file exists and has a non-zero size string is not the null string strings S1 and s2are the same strings S1 and s2are not the same descriptor fd associated with terminal file exists and has set-UID bit set file exists and is writeable file exists and is executable string has zero length Expressions may be joined by ! logical negation —a logical and —o logical or \(expr\) grouping parentheses (escaped from shell Trap Command The trap command is used to capture control in case of an error or other program interruption. In UNIX terminology this is called catching a signal. These signal numbers are described under the kill command in Appendix B. One exception, the kill signal (number 9), cannot be captured. Syntactically, you specify the command(s) to be executed if the signal occurs as the first argument to trap followed by a list of signal numbers. For the shell variable loops. Then it uses a while loop to invoke the remaining command. After each iteration. expr is used to decrement the loop count. Once the count reaches 0. the loop is terminated. Conditional Statements If Statement The if statement can be used to evaluate the result of the execution of a command and take an action based on the truth value of this result. The most basic form of the if statement is as follows: if cmdl then cmd2 fi In this case, cmd1 is executed, then if the result was true, cmd2 is executed. Otherwise, control is transferred to the statement following the fi. For example, if we wanted to add a message to indicate successful completion to the append script from the Parameters & Variables section, we could do the following... # append version 5 fn=${1:-${afile:?”filename req’d”}} echo “appending to $fn” NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 34 of 45 May 15, 2012 Copyright © 2002-2012 echo “control—D to terminate:” if cat >>$fn ; then echo “append successful" fi The message append successful is printed if’ the cat command returns a true exit status (in other words, worked successfully). A more sophisticated example might take advantage of the command test. read reads one line from standard input to variables on the read command line. One variable. with any leftover words assigned to the last the shell command read and input and assigns words of word is assigned for each variable. The test command evaluates an expression and returns the value true if the expression is true, false otherwise. These expressions are made by combining operators, commonly called primitives, with filename and string operands. See the reference section for a complete list of primitives. Note that there are two ways to write a test. The following two lines both test to see if the two shell variables, $1 and $stuff. are identical. They are equivalent and can be used interchangeably. test $1 = $stuff [ $1 = $stuff ] In the following example, the script erm first echoes the passed parameters, asks for confirmation and then deletes all the files specified in the passed parameters if the answer to the confirmation request is y. # erm echo “About to remove:” echo $* echo “Enter ‘y’ to remove” read answer if test “$answer” = y ; then rm $* fi The quotes around $answer act as a placeholder. This handles the case where the user entered no answer, but instead hit return in response to the read command. The indenting is cosmetic. An alternative to write this. script is: # erm version 2 echo “About to remove:” echo $* echo “Enter ‘y’ to remove” read answer if [ $answer = y ] then rm $* fi The differences are the use of [] instead of test and the introduction of then on the same line as the test. Using conditionals and test can further modify append to verify that the specified file even exists before attempt to append to it. The -f primitive of test can be used to test for the existence of a regular file. The exclamation point (!) is used to negate the truth value of an expression. The exit shell command is used to terminate a script. It returns its argument to the script where zero is true and non-zero is false. append version 6 fn~${1:-${afile:?”filename req’d”}} if test ! —f $fn ; then echo “$fn doesn’t exist” exit 1 fi NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 35 of 45 echo "appending to $fn” echo "control-D to terminate:” if cat >> $fn then echo “append successful” fi The full form of the if statement is as follows (where [] are used to indicate optional expressions): if cmdl then cmd2 [elif cmd3 then cmd4]... [else cmdsn] fi Using this form of the if statement, we can add a message in response to a request to not continue with the remove. # erm version 3 echo “About to remove:” echo $* echo “Enter ‘y’ to remove files” read answer if [ $answer = y ] ; then rm $* else echo “remove aborted” fi While Statement The while command repeatedly executes a command and each time the execution returns a true exit status a second set of commands is executed. The while command takes the following form: while cmd1 do cmd2 done As long as the execution of cmd1 returns a true exit status, cmd2 is repeatedly executed. A simple way to use while is creating a loop that will be executed forever. In the following example, a process status (ps) command is executed every 60 seconds. The tput command clears the screen before each execution of ps. while sleep 60 do tput clear ps -a done Another example uses while and the built-in shell shift command to print the arguments to a command. The following script prints the arguments passed to it. # printarg echo “$0 called with $# arguments” echo “They are:” while [ $# —gt 0 ] do echo “ “ $1 shift done NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 36 of 45 May 15, 2012 Copyright © 2002-2012 Until Command The until command has exactly the same syntax as the while command. The only difference is that an until loop is executed as long as the command returns false rather than true. The following script will check for the existence of a specified file. It checks every 60 seconds and once the file exists, it is displayed. # exprint until test —f $1 do sleep 60 done cat $1 For Command The for command can be used to sequentially process a set of strings. It successively assigns a string to a shell variable from a specified list of strings and then performs a specified loop. Here is the basic syntax: for name [in strings ] do cmds done Note that the brackets are not part of the command. They indicate that the contained information is optional. If in strings is not specified, all arguments to the shell file ($*) are used. The following shell script takes a list of filenames as arguments and displays whether they are readable. It uses the -r primitive of test. # canread for x ; do if [ —r $x ] ; then echo “$x is readable”, else echo “$x cannot be read” fi done It is possible to generate a set of strings for the for command by executing another UNIX command. For example. the following script performs the same readability test but it is performed on files whose names are in a file specified on the command line. The cat command is used to read this file and supply its contents to the for command. # canread2 for x in ‘cat $1’ do if test —r $x ; then echo “$x is readable” else echo “$x cannot be read” fi done Case Command The case command selects a set of commands to execute by matching cases to a control string. If the control string matches a case pattern, the associated commands are executed. The form of the case statement is: case string in pat!) eomniands1:; NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 37 of 45 pat2) (omrnands2;; esac string is successively compared to pat1, pat2,... until a match is found. When there is a match, all commands up to a double semicolon (;;) are executed. The shell wildcards * and ? can be used in patterns as well as the [] notation for selection. Also, the I (or) symbol can be used to indicate that if either expression matches, it is considered a match. For example, the following commands print a greeting based on the current hour returned by the date command. hour=’date +%H` case $hour in 0?|1[0l]) echo “Good Morning”;; l[2—7]) echo "Good Afternoon”;; 18) echo “Dinner Time!”;; *) echo “Good Evening”;; esac Note that the * pattern is used as the alternative if all else fails. As it will match anything. If used, it must appear as the last choice. Shell Functions Starting with System 5. Release 2. shell functions have been available. A shell function is an alternative to placing shell commands in a file to make a shell script. Functions vs. Scripts The biggest advantage of shell functions over shell scripts is fast execution. As they are saved in the data area of the current shell, a file sy stem search is not required in order to locate and execute them. On the negative side, shell functions are always local to the shell that defined them. This means that each shell you create must redefine the functions if it needs access to them. Another way shell functions differ from shell scripts is their access to shell variables. Because a shell function is executed by the current shell whereas a shell script is executed by a sub-shell, functions have access to all the variables of the current shell. This means, for example, that a cd command in a shell function will change your current directory and it will stay changed after the function has completed execution. A cd command in a shell script is only effective for the execution life of the script. Defining a Function The general syntax to define a function is: func( ){ list;} where func is the function name and list is a list of shell commands that form the function definition. Note that a space is required following the opening brace in the definition. If the closing brace does not appear on the same line as the last command in list, the semicolon is optional. The following function looks for matching lines in a file named .fone in your home directory; and then in /etc/fone. Note that the word “$*“ is a special variable that means substitute all parameters here but put quotes around the outside of NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 38 of 45 them so they are treated as a single argument to the grep command. This means that the function will pass multiple words to grep in a single argument which makes lookups of, for example. John Smith possible. phone() grep $*“ $HOME/.fone /etc/fone The function phone was entered on three lines. Once the first line was entered (which must include the opening brace ({)) the shell prompted with its secondary prompt string (> by default) until a matching close brace was encountered. You could have also entered the function on one line, but if you did. you need to remember the space following the { and the required before the }. Where to Define Functions If you enter a function definition from the command line, it will exist for the life of the current shell. Generally. however, it is desirable to either always have functions defined or have a set of canned functions that you can define easily when desired. You can enter functions that you want always defined into your .profile. This means that whenever you log on. the definitions will be interpreted. If you have various sets of functions that may be useful i/o a particular project. you can include them in files. i.e.. put all related function definitions in one file. Then you can use the dot (. command to activate the definitions when desired. You may also want to modify your prompt string to indicate that a particular set of functions has been activated. For example, if you are working on a book, you could put all the functions and other shell commands to set up your environment the way you want it for working on the book in one file. You can then activate these definitions using the dot command. Here is an example: # .book - Setup book envirionment cd /usr/me/Book PS1=”Book > “ draft() { nroff -mm bhdr $* | lp } final() { troff -Tps —mm bhdr $* | devps > /tmp/BK$$ echo “cutput in /tmp/BK$$” } Status of Definitions If you define shell functions you may not remember which ones are defined or what the definition contains. You can use the set command to find out. A set command with no arguments displays all currently defined shell functions as well as shell variables, If you find that you want to remove a definition you can use the unset command. For example. to remove the definition of the shell function draft from the current shell you would enter: unset draft Search Order When you enter a command, the shell first checks to see if it is one of the commands built into the shell. Second, it checks to see if it is a shell function. If the command isn’t a built-in or a shell function, the shell searches the NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 39 of 45 directories listed in sour PATH shell variable in the order listed to try” to locate the command. This means that shell functions override commands that are stored in files but built-in commands always override shell functions. The type command, a shell built-in command, can be used to determine where the shell will locate a command. Just enter type followed by the command name and the shell will display where it located the command. Command Line Shell Invoking In the previous sections the shell has been treated as either the command interpreter waiting for you command when you log on or as an interpreter of scripts that is invoked by entering the name of the script. Actually, the found in the current shell value of the /bin/sh. shell is just another UNIX command. Its name is sh and it can be /bin directory. When you enter the name of a shell script, your invokes a new shell (sub-shell) to interpret it. Your shell uses the variable SHELL as the pathname for the new shell. The default is Like most UNIX commands, there are various options that can be placed on the invocation line for the shell. Many of these options can be changed within your current shell by use of the set command. In this section you will learn about the invocation options and using the set command. The place where you will most likely use the capability of invoking another shell using the sh command is in debugging shell scripts. This is covered at the end of this section. Invoking A shell is created by” entering sh at the command prompt. If it is started with no arguments, it becomes your current shell, issues a command prompt and ails for user input. It is terminated by a control-D or the exit command. You can determine if you are running multiple shells by using the PS command. For example, if you typed in the following: PS sh PS exit PS In this sequence. the second ps command shows that you have one more shell than the other ps commands. Assuming you are in your login shell when you typed this sequence, the first and third ps commands show one shell, the second ps shows two. If you invoked sh with an argument. that argument is taken to be a file name that contains shell commands and the contents of that file are interpreted. In the section on simple scripts, the first example was a script called ww. It contained: date who We invoked it by adding execute permission to it with the command chmod +x ww and then executing it by entering its name. An alternative is to enter the command: sh ww NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 40 of 45 May 15, 2012 Copyright © 2002-2012 The result is the same and we don’t need to set execute permission. For a production script, entering sh every time is cumbersome but this capability is very useful for testing new scripts. This brings us to the subject of debugging. Debugging When an error occurs in a script the error message is displayed but you may have no idea which line in the script produced the error. For example. if a script contained multiple occurrences of the cat command and you received an error from cat y ou might not be able to tell which occurrence caused the error. The -v option can be used to print each script line as it is being read by the shell. As an example. let’s say you create a script called earg that consists of: # earg echo $1 echo $2 If you enter... sh earg first second the following will be displayed: first second If you enter... sh -v earg first second the following will be displayed: echo $1 first echo $2 second Another useful debugging option is -x. This option displays commands as they are to be executed, after substitution has occurred. Using the same script as above, if you entered the command sh -x earg first second your output would be: +echo first first +echo second second The + is prepended to the command lines by the shell to show you that these are the lines after substitution. Or, if you enter the command sh -xv earg first second you get: echo $1 +echo first first echo $2 +echo second second A third option useful for debugging is -u. This causes a reference to an unset variable to be treated as an error. This option is handy for finding spelling errors in variable names within a script. Again, Using earg. if you enter the command sh -u earg first second, the script executes as usual, but if you left off the second argument to earg and enter NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference May 15, 2012 Copyright © 2002-2012 Pg 41 of 45 Linux Bash Command Reference Sheet sh —u earg first your output is: first earg: 2: parameter not set This message tells you that there was a reference to shell variable 2. which was not set. If you use both the -u and the -v options, you would see the line w here the error occurred. NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 42 of 45 May 15, 2012 Copyright © 2002-2012 Filesystem cd [-] [directory] ·Change directory :Change to the previous directory you were in chmod [opts] <mode> <filepattern> ·Change permissions -R :Change permissions recursively chown [-R] <user>[.group] <file> ·Change ownership -R :Change ownership recursively cp [opts] <from> <to> ·Copy files and directories -i :Interactive mode. Prompt before overwriting -p :Preserve file permissions and ownership -R :Copy directories recursively df [opts] [device name] ·Print filesystem usage info -a :Show all filesystems. -h :Human readable format. Quantify byte information. -i :Show inode usage info. du [opts] [pattern] ·Show space usage on files and dirs -c :Produce a grand total for all arguments. -h :Human readable format. Quantify byte information. -s :Summarize. Only show a total for each argument. -S :Do not include size of subdirectories. find <path> [-name ‘pattern'] ·Search for a file. Ex: find /home –name ‘index.html’ –perms –644 -ls gzip [opts] <filepattern> ·Compress a file or files -1..9 : Set compression level. 9=highest, 1=lowest. -d :Decompress file. Same as the gunzip command. -l :List the statistics for a compressed file. ln [opts] <tofile> <linkfile> ·Create a sym/hard link -s :Create a symbolic link between files. (alias name) -f :Force creation, even if the link file exists. ls [opts] [pattern] ·List file and directory entries -a :List all files including . and .. -d :List directories themselves, not their contents. -l :Long list. Shows permissions and modified time. -r :Recusively list files in directories. -S :Sort output by file size. -u :Sort by the last access time. -X :Sort by filename extension. -1 :Print output files one per line. --time=atime :Show last access timestamp for file. mkdir [opts] <dirname> ·Make a new directory -m mode: Set the initial permissions to mode. -p :Create parent directories if they don’t exist. mv [-i] <frompattern> <tofile> ·Move/Rename a file -i :Interactive move. Prompt before moving files. rm [opts] <filepattern> ·Remove a file -f :Force removal. Don’t ask if it’s ok to remove. -i :Interactive remove. Prompt before each file. -r :Recusively delete directories an their contents. tar [opts] [tarfile] [pattern] ·Create an archive c :Create mode. Create a tar archive. x :Extract mode. Untar archive contents. t :List mode. List the contents of the archive. f :Specify a tarfile to use. v :Verbose mode. Show files being added or untared. z :Compress. Filter input/output through gzip. touch [opts] <pattern> ·Update the timestamp on a file -a :Only change the access time on the file. -t :Specify a timestamp to use instead of current time - Information & Print date [opts] ·Print or set the system date and time --date=STRING :display time described by STRING. --set=STRING :set time described by STRING. dmesg [opts] ·Print or control the kernel ring buffer -c :Clear the contents of the ring buffer. file [opts] [filepattern] ·Determine the file type -z :Try to look inside compressed files. finger [opts] [userpattern] ·Show info about system users -m :Match the exact username specified. free [opts] ·Display free and used memory in the system -b :Display the information in bytes. hexdump [opts] ·Show all the characters of a file -c :Display the input offset in hexidecimal last [opts] [username] ·Show last system logins for users -num :Show last num of sessions. -a :Display the hostname in the last column. -d :Translates IP numbers to their hostname. -f <file> :Use file as last log. less [opts] [filepattern] ·View a file a page at a time -i :Do case insensitive searching. -S :Don’t wrap long lines. man [opts] [section] <manpage> ·View online manual pages. -a :View all available manual pages for name. -k string :Search for the specified string. md5sum [opts] [filepattern] ·Show the uniqueness of files ps [opts] ·Show what processes are running on the system a :Select all processes on a terminal. u :Display user oriented format. More columns. x :Select processes without a controlling TTY. w :Show an extra line of process entry per w. Ex: ps auxwww =Displays all process information on system. quota [opts] [user] ·Display disk usage and limits -v :Display filesystems where no quota is set. time [opts] [command] ·Show resource usage for a command top [opts] ·Display top CPU processes every X seconds -d sec :Set the delay to sec seconds before refreshing. uname [opts] ·Show OS and system information -a :Show everything uptime ·Show system uptime and load w [opts] [user] ·Show who is logged in/what they are doing whereis [command] ·Locate the related files for a command which [command] ·Show full path to the specified command who [opts] [args] ·Show who is logged in Text - Edit / Search / Filter awk [opts] [exp] ·pattern scanning and processing language -Ffs :Set the field separator for commands. Ex: cat access_log | awk {‘print $1’} (prints hostnames) Do a ‘man awk’ for more information and examples. cat [opts] [filepattern] ·Print file contents on STOUT -E :Display a $ at the end of each line. -T :Show tabs as ^I. -v :Show non-printing characters. comm [opts] [file1] [file2] ·Compare two sorted files -1 :Suppress lines unique to left file. -2 :Suppress lines unique to right file. -3 :Supress lines unique to both files. csplit [opts] [file] [pattern] ·Split a file on context -f prefix :Use prefix instead of xx in output filenames. -n digits :Use digits number of digits instead of 2. -z :Remove empty output files. Ex: csplit mailspoolfile "/^From /" {*} cut [opts] [filepattern] ·Remove sections from each line -c range :Output only the characters in range Ex: cut –c 1-80 file (truncate lines at 80 characters) diff [opts] [file1] [file2] ·Differentiate two files Ex: diff program-old.c program.c > program.patch echo [opts] [string] ·Print a line of text -e :Enable interpretation of backslashed sequences. -n :Don’t automatically insert a newline character. grep [opts] [pattern] [file] ·Print lines matching pattern -B num :Print num lines of leading context on matches. -C num :Print num lines of trailing context on matches. -E :Interpret pattern as an extended regular expression -i :Do case insensitve matching. -l :Just print the files that match the pattern. -r :Read all files under each directory recursively. -v :Print the lines that don’t match pattern. head [opts] [file] ·Print the first part of a file -n num :Print the first num lines instead of the first 10. nl [opts] [file] ·Number the lines of a file patch [opts] <[patchfile] ·Patch a file using a diff file sed [expression] [file] ·Stream editor Ex: cat file | sed ‘s/frompattern/topattern/’ > output sort [opts] [file] ·Sort lines of text files -n :Compare according to string numerical value. -r :Reverse the result of comparisons. split [opts] [file] ·Split a file into pieces -l num :Put num lines per output file. tail [opts] [file] ·Print the last lines of a file -f :Output appended data as the file grows. -n num :Print last num lines of a file instead of last 10 tr [opts] <set1> [set2] ·Translate char. from set1 to set2 Ex: cat index.html | tr A-Z a-z > index-new.html uniq [opts] [input] [output] ·Remove duplicate lines -c :Prefix lines with number of occurances. -d :Only print duplicated lines. -u :Only print unique lines. wc [opts] [file] ·Print the number of lines in files, etc. -m :Print the character count. -l :Print the line count. -w :Print the word count. -L :Print the length of the longest line. Communication & Network ifconfig [devicename] [action] [options] ipchains [opts] ·Manip. ipchains firewall(kernel 2.2+) iptables [opts] ·Manip. iptables firewall(kernel 2.4+) mail [opts] [address] ·Send mail from the command line -s subject :Specify the subject as subject. -c list :Send carbon copy to list of users. -b list :Send blind carbon copy to list of users. Ex: echo “Meet me at noon.” | mail –s “Reminder” –c \
[email protected],
[email protected] [email protected] netstat [opts] ·Print network connections and info -a :Show both listening and non-listening sockets. -n :Do not attempt to resolve IP addresses. -t :Only show tcp socket connection table. ping [opts] [host] ·Send ICMP packets to network hosts -c count :Send count number of packets and then quit. -i sec :Wait sec seconds between sending packets. route [opts] [target] ·Show/Manipulate IP routing table -n :Show numerical addresses instead of hostnames. scp [opts] [[host:]fromfile] [[host:]to] · Secure copy -C :Compresses the data that is sent over the session. -r :Recursively copy directories. ssh [opts] [[user@]host] [command] · Secure shell/login -C :Compresses the data that is sent over the session. sniffit [opts] ·Record TCP network traffic -i :Interactive mode. Shows all traffic. -l <length> :Set the maximum sniff length to length. -p <port> :Specify the port number on the target host. -s <source> :Set the source IP from which packets come. -t <target> :Set the IP to which packets are going. tcpdump [opts] [expression] ·Dump traffic on a network telnet [opts] [host] [port] ·Open TCP socket to a host -n <file> : Opens file for recording trace information. -x :Turns on encryption of the data stream if possible. traceroute [opts] [host] ·Show the route packets take -n :Don’t do DNS lookups of the IP addresses. wget [opts] [URL] ·Make a HTTP request from the shell -r :Recursive get the URL and all it’s links. -k :Convert the non-relative links to relative ones. whois [opts] <arg[@server]> ·Query a whois database Ex: whois domain.com whois
[email protected] whois
[email protected] Bash Shell > ·Send STDOUT to a file. overwrite/create a file Ex: ls –l > list-of-files.txt >newfile >> ·Send STDOUT to a file, appending to te end of the file Ex: ps aux > pslog.txt date >> pslog.txt | ·Send the STDOUT from a command to the STDIN of another Ex: cat listofnames | sort cat access_log | awk {‘print $1’} | sort | uniq 2> ·Send STDERR to a file, overwriting the filename Ex: startx 2> .errorlog alias ·Create a command alias in the shell Ex: alias ls=’ls –la –-color=auto’ cd [-] [directory] ·Change the current working directory - :Change to the previous directory you were in. clear ·Clear the terminal display env [opts] [command] ·Run command in modified environment export [opts] [variable] ·Export an environment variable Ex: export TERM USERNAME PS1 MAILSPOOL export TERM=vt100 for ·Execute sequence of commands for a list of items Ex: for i in *.mp3 ; do mpg123 $i ; done for n in 1 2 3 4 ; do mkdir $n ; done history ·Show the command history up til now nice [opts] [command] ·Set the OS process priority Ex: nice 19 gzip access_log (lowest priority on Linux) Ex: nice –20 kswapd (real time priority on Linux) pwd ·Print out the current working directory renice [opts] <arg> ·Change priority of a running process -p PID: Specify a process id to renice Ex: $ ps auxw | grep gzip 6319 ? S 0:20 gzip bigfile.txt $ renice 19 –p 6319 reset ·Initializes the terminal as if you just logged in set ·Set a shell option or variable (run ‘help set’) sleep ·Pause for specified period before continuing Ex: ps aux ; sleep 3600 ; ps aux umask ·Set the default file permissions Ex: umask 022 (files will be created 644 by default.) while ·A loop that runs commands while a condition is true Ex: while (true) ; do ps auxw ; sleep 1m ; done > pslog xargs [opts] [command] ·Execute a command for each arg -n number :How many arguments to give each command run. -p :Prompt the user before each command is run. -d -g -G -s Admin adduser [opts] <username> ·Add a user to the local system <dir> : Set the home directory for the user to dir. <group> : Set the primary group for the user to group. <group,group,…> : Set additional groups for the user. <shell> : Set the default shell for the user to shell. chfn ·Change the finger information for a user chsh ·Change the shell used for the user edquota [opts] <user> ·Edit a user’s or group’s quota -g : Edit the group quota instead of user quota. kill [-signal] <pid> ·Terminate a process/Send it a signal -HUP,-1 : Signal usually makes process to reread config. -9 :Send a SIGKILL, process must die. -l :Print a list of signal names and numbers. killall [-signal] [name]·Kill processes by name -e :Require an exact name of a process. -i :Interactively ask for confirmation before killing. ldd [opts] [program] ·Show a programs library dependencies mount [opts] <device> [mountpoint] ·Mount a file system -o <opts> : Specify options for mounting. Listed below. loop remount ro, rw user – Mount a disk file such as a CD-ROM image or floppy image. Remount the filesystem with new options Mount filesystem in readonly or read-write mode. Allow normal users to mount this filesystem. -r :Mount the filesystem read-only. Same as ‘–o ro’ -t <vfstype> :Specify the type of filesystem to mount. ext2, ext3 vfat iso9660 nfs – – – – Native Linux partition types. Windows 9x 32-bit partition type. CD-ROM filesystem. Network remote filesystem. passwd [opts] [username]·Change user’s system password -l :Lock the password for the account. -u :Unlock the password for the account. -S :Show the status of the password for the account. su [-] [username] ·Switch users or login as the superuser - :Make shell a login shell -c <command> : Run command as username. umask [opts] [mode] ·Set the default file permissions -S :Show current symbolic umask. umount [opts] [path/device]·Unmount a mounted filesystem -f :Force unmounting (in case of unreachable NFS system). NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 43 of 45 May 15, 2012 Copyright © 2002-2012 Notes __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 44 of 45 May 15, 2012 Copyright © 2002-2012 Notes __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ NeatInfo.com - by: Jan Zumwalt BASH SHELL Reference Pg 45 of 45 May 15, 2012 Copyright © 2002-2012