Linux Shell Commands Cardiff School of Computer Science & Informatics Documentation & Facilities Toggle navigation Home Documentation Software Services Contact Linux Shell Commands The Shell is the command interpreter on Linux systems. This document intoduces some of the basic features of the Shell and lists many of the commands or programs available on the Linux computers in Cardiff School of Computer Science & Informatics. The Shell The Linux command interpreter or shell is the program users interact with in a terminal emulation window. The terminal emulation window can be one in the workstation's Graphical User Interface mate-terminal on Linux. Alternatively, it can be an application such as SSH secure shell client or PuTTY on a Windows PC that's logged into Linux over the network. The shell used in the School of Computer Science & Informatics is bash Bourne Again Shell. There are other shells available such as the Bourne Shell, the C-Shell and the TC-Shell, and you can choose to use a different shell if you prefer. They all have similar characteristics but each has its own particular features. This document assumes you are using bash. Bash has the following features: A command prompt which may be configured by the user. The default prompt is a dollar symbol preceded by "bash" and the bash program's version number. bash-2.05$ The shell, like other programs on Linux has an associated current directory. Programs running on Linux use the current directory as the starting point when locating files. The shell command cd is used to change the current directory to a different location in the Linux file system. Commands are invoked by naming them. Most Linux commands are simply programs which are executed by the shell. For example, to run the ls command which reads the the current directory and lists the names of its files the following would be used. bash-2.05$ ls When you type a command name, the shell will check to see if the command is built-in and will otherwise search a set of directories until it finds the program. This set is known as the search path. The search path includes the current directory, your home directory and its subdirectory "bin". You can write your own programs and invoke them simply by typing their names. If you store such a program in the directory ``bin'' it will be found and run no matter what your current directory is. Commands often have argument strings which may, for instance, represent filenames. For example, the below command changes the current directory to "bin" in your home directory. The tilde character means your home directory to the shell. bash-2.05$ cd ~/bin Some commands need more than one argument. For example, the copy command takes two arguments the file to copy and it's destination. This is shown below where fileA is copied to a new file, fileB. bash-2.05$ cp fileA fileB Some commands have flag or option argument strings usually beginning with ``-'' or ``-''. The flags modify the behaviour of the program being invoked. The below command when invoked makes ls give a long listing of files sorted by time of creation. bash-2.05$ ls -lt The shell will expand wildcards to match filenames in the current directory. For example, to give a directory listing of the file with names "anything.c" use the following. bash-2.05$ ls -l *.c Most Linux commands and programs adhere to a concept of standard input and standard output. The standard input is a stream of data which the program reads and the standard output is a stream of output written by the program. Often these are both attached to the terminal so that input comes from your keyboard and output goes to your screen. The shell lets you redirect the standard input and output. bash-2.05$ cat < fileA bash-2.05$ cat < fileA > fileB The Shell has the facility to pipe the output of one program to the input of another. The pipe symbol is "|". For example to count the number of words in fileA we can cat the file then pipe the output in the wc program. bash-2.05$ cat fileA | wc -w 405 You may assign aliases for commands or groups of commands that you may execute frequently or find cumbersome to enter. For example we could assign an alias "countc" to count the number of C program source files in the current directory using ls to list the files and wc to count the number of lines output. alias countc="ls -l *.c | wc -l" The shell has string and numeric valued variables. bash-2.05$ x="Hello World!" bash-2.05$ echo $x Hello World! Some variables are pre-set, e.g. $HOME is your home directory. Type set to see a list of assigned variables. Bash is an interpretive programming language with while loops, for loops, if-then-else statements and many more. See the Linux on-line documentation for more details by typing the following command. bash-2.05$ man bash Scripts of shell commands can be written. These can be invoked in the same way as compiled programs (i.e. just by naming them). For example, to create a script that counts the number of C program files in the current directory we first create a file in ~/bin containing the following. #! /bin/bash ls -l *.c | wc -l We must then make the file executable using the chmod command before we can run it like normal. bash-2.05$ chmod +x ~/bin/countc bash-2.05$ countc 45 The shell has ``job control''. Programs which don't require any terminal interaction can be run in the background. bash-2.05$ sort bigfile > sortedfile & [1] 3470 The above puts the program sort in the background and the shell is available immediately for other commands. The shell prints the job control number ("1" in this case) and the process identity number ("3470"). The special character Ctrl + z can be used to suspend a program which is running in the foreground. Once stopped the bg command can be used to put the program in the background or fg can be used to continue it in the foreground. If you have more than one job running in the background or suspended, you can refer to them by their job number. To see your jobs and their job numbers use the jobs command to list the status of all stopped or background jobs. The shell has a history mechanism, it remembers the last few commands. The history command can be used to list the last few commands executed along with a reference number. bash-2.05$ history 515 cd ~ 516 ls -lrt 517 ps -ef 518 pdflatex myfile.tex In a workstation's terminal emulation windows, you can cut and paste from the history to rerun a command. You can also use the symbol ``!'' to rerun any command from the history. bash-2.05$ !518 # rerun command number 518 from the history bash-2.05$ !ps # rerun the last command starting "ps" bash-2.05$ !! # rerun the last command See the manual page on bash for more details (type man bash). Bash has an additional mechanism which allows you to recall and edit previous commands using the keyboard up-arrow key. If you press up-arrow, the last command re-appears on the terminal. Press up-arrow again to get earlier commands. To rerun the command, press RETURN. To amend the command before rerunning it, use the delete key to remove characters from the end or use the back-arrow key to reposition the cursor to delete or insert characters within the command. Shell Commands Here is a summary of some of the commands available. For more details refer to the manual page of each command. You can see these on-line by using the man command. Just type man followed by the name of the command you want to see. Logging out Command Description logout log out of a Linux terminal Note, on a Linux workstation you will need to exit the Desktop Environment instead. Files and Directories These commands allow you to create directories and handle files. Command Description cat concatenate and print data lpr spool file for line printing cd change current directory lprm, cancel remove jobs from line printer queue chgrp change file group ls list and generate statistics for files chmod change file mode mkdir make a new directory cp copy file data more, page display file data at your terminal Command Description file determine file type mv move or rename files find find files pwd print working directory grep search file for regular expression rm, rmdir remove (unlink) files or directories head give first few lines tail print last lines from file just text justification program touch update access and modification times of a file lpq spool queue examination program File Editors Editors are used to create and amend files. Command Description emacs GNU project Emacs xemacs emacs with mouse action ex, edit line editor Command Description pico easy text editor for vdus pluma Mate GUI text editor gedit GNOME text editor vi, vim standard text editor Vi, pico and emacs are screen-based editors which run on a vdu or in a workstations terminal emulation window; pluma, gedit and xemacs are graphical user interface (GUI) based editors with cut and paste and mouse-controlled cursor positioning. Manipulating data The contents of files can be compared and altered with the following commands. Command Description awk pattern scanning and processing language perl data manipulation language cmp compare the contents of two files paste merge file data comm compare sorted data sed stream text editor cut cut out selected fields of each line of a file sort sort file data diff differential file comparator Command Description split split file into smaller files expand, unexpand expand tabs to spaces, and vice versa tr translate characters gawk pattern scanning and processing language uniq report repeated lines in a file join join files on some common field look find lines in sorted data wc count words, lines, and characters Compressed files Files may be compressed to save space. Compressed files can be created and examined. Command Description gzip compress files zmore file perusal filter for crt viewing of compressed text uncompress uncompress files Command Description zcat cat a compressed file gunzip uncompress gzipped files zcmp, zdiff compare compressed files Information Manuals and documentation are available on-line. Go to our web site www.cs.cf.ac.uk/systems for web-based documentation. The following Shell commands give information. Command Description apropos locate commands by keyword lookup man displays manual pages online Command Description info displays command information pages online yelp GNOME help viewer Status These commands list or alter information about the system. Command Description ps print process status statistics date print the date quota -v display disk usage and limits reset reset terminal mode du print amount of disk usage script keep script of terminal session stty set terminal options groups show group memberships time time a command homequota show quota and file usage iostat report I/O statistics tty print current terminal name Command Description kill send a signal to a process uptime display system status last show last logins of users users print names of logged in users lun list user names or login ID vmstat report virtual memory statistics netstat show network status w show what logged in users are doing who list logged in users printenv display value of a shell variable Printing Files can be printed using shell commands, using the GUI print manager, or direct from some applications. You must specify a printer by name. Printers are called Printer Name Location tl1_lw Teaching Lab 1 (C/2.04) laser printer tl3_lw Teaching Lab 3 (C/2.08) laser printer Printer Name Location tl2_lw Teaching Lab 2 (C/2.05) laser printer tl4_lw Teaching Lab 4 (C/2.10) laser printer Most commands which can be used to print files, expect the printer name to be given following a -P argument. Files may be sent to the printers as simple text files or they may be processed in various ways for the laser printers. Command Description lpr -Pprinter send a file to a printer dvips -Pprinter postprocess TeX file into Postscript and print on laser printer a2ps -Pprinter format text file in PostScript and print on laser printer Messages between Users The Linux systems support on-screen messages to other users and world-wide electronic mail. Command Description write send a message to another local user wall send a message to all local users Command Description pine vdu-based mail utility mail simple send or read mail program thunderbird GUI mail handling tool on Linux Networking The School of Computer Science & Informatics is connected to the JANET Internet Protocol Service (JIPS), the UK Universities' network. These commands are used to send and receive files from Campus Linux hosts and from other hosts on JIPS and the Internet, that permit such connections, around the world. Command Description ftp file transfer program tftp trivial file transfer program sftp secure shell file transfer program rcp remote file copy scp secure shell remote file copy wget non-interactive network downloader Command Description telnet make terminal connection to another host ssh secure shell terminal or command connection rlogin remote login to a Linux host rsh remote shell curl transfer data from a url firefox web browser google-chrome web browser These commands work only where the remote host permits such connections. Programming The following programming tools and languages are available. General Command Description make maintain groups of programs size print program's sizes Command Description nm print program's name list strip remove symbol table and relocation bits C Command Description cb C program beautifier gcc GNU ANSI C Compiler Command Description ctrace C program debugger indent indent and format C program source cxref generate C program cross reference C++ Command Description g++ GNU C++ Compiler JAVA Command Description appletviewer JAVA applet viewer javac JAVA compiler eclipse Java integrated development environment on Linux FORTRAN Command Description f95 GNU Fortran 95 compiler Other Languages (Not available on all systems). Command Description bc interactive arithmetic language processor matlab maths package gcl GNU Common Lisp perl general purpose language Command Description python object-oriented programming language squeak smalltalk php web page embedded language mathematica symbolic maths package asp web page embedded language Text Processing TeX is a typesetting language used extensively in Linux and other operating systems for producing high-quality printed documents. Another set of programs based on Troff is the standard Linux text formatting family used, for example to format manual pages. General Commands Command Description fmt simple text formatter evince GNOME PostScript previewer Command Description acroread PDF viewer spell check text for spelling error aspell interactive spelling checker Troff Command Description eqn mathematical preprocessor for troff tbl prepare tables for nroff or troff grap pic preprocessor for drawing graphs troff text formatting and typesetting language Command Description nroff text formatting language groff GNU troff interface for laserprinting pic troff preprocessor for drawing pictures TeX Command Description tex text formatting and typesetting latex latex formatter Command Description pdflatex latex formatter with PDF output xdvi dvi previewer dvips convert a DVI file to POSTSCRIPT Word Processing LibreOffice is available on the School's Linux systems and attempts compatibilty with Microsoft Office. Command Description libreoffice start LibreOffice applications Database Management MySQL and Oracle are available. Command Description sqlplus run the Oracle SQL interpreter mysql run the mysql SQL interpreter sqldeveloper Oracle SQL Developer GUI interface mysql-workbench GUI interface for MySQL Overview The Shell Shell Commands Logging out Files and Directories File Editors Manipulating data Compressed files Information Status Printing Messages between Users Networking Programming General C C++ JAVA FORTRAN Other Languages Text Processing General Commands Troff TeX Word Processing Database Management Back to top Tags linux shell ubuntu Tags linux shell ubuntu Cardiff University is a member of the Russell Group of Universities Cardiff University is a registered charity No. 1136855 Copyright © Cardiff University Accessibility Feedback Cookies Privacy Policy Terms of Use
