Unix / Linux commands

Unix command Description Details ALIAS Create abbreviations (aliases) for commands alias abbreviation=command Displays a list of all aliases, standard arguments can be used (-a, -l, etc.). To cancel the alias use the unalias command. F.e. alias my_command='ls -al'. ARCHIE Change the current directory archie filename Search the Archie database for a file on a FTP site. AT Execute a command at a specified time at [-filename][-m] time -filename - Read the command(s) from the file specified. -m = Notify the user by mail when the job is completed. time = The time when the commands are going to be executed. BC Use the calculator bc To use decimals, type scale = number (of decimal digits). End the calculator with Ctrl-D. BG Execute processes in the background bg [%n] %n = Without this parameter it displays the jobs that are currently executed in the background. With a number the process with the given number is executed in the background. & = At the end of a command starts the process in the background. CAL Display the calendar of the current month cal [month][year] CANCEL Cancel requests for printing cancel [ -u user] print-request Requests can be cancelled by using the printer-id or by specifying the printer name. -u user = Cancel print jobs that are queued for the specified user. CAT Display one or more files cat [-sn] [filenames] If more than one filename is supplied, it is added at the end of the previous file and displayed. -n = Display numbers in ascending order in front of each line. -s = Do not comment about nonexistent files. filenames = The filename(s) in the order that you want them to be displayed. CD Change the current directory cd [pathname] Change the current directory to pathname or to root directory if no pathname is given. CHGRP Change group name chgrp groupname filename(s) | directory name(s) Change group of the named file or directory. CHMOD Set file access permissions chmod [ugo,+-,rwx] filename | directory name Change mode permissions of the named file(s) or directory(ies). See File permissions for detailed information. CHOWN Change owner chown username filename | directoryname Change the owner of a file or directory. CHSH Change shell chsh Change the Unix shell you log into. CLEAR Clears display clear Clears the display. Only the prompt is displayed. CMP Compare files cmp filename filename Compares the named files. If they are equal nothing is returned, otherwise it returns the first character and line where the two files differ. COMPRESS Compress file compress [-v] filename Compress the named file. The compressed file gets .Z appended to the filename. -v = Ask for verification after compressing the file. CP Copy a file cp oldname newname [-r][-i] pathname (cp index.html index1.html) The cp command allows you to copy files to new files, or copy files and directories to new directories. The command line cp index.html otherdir will copy the file index.html to the directory otherdir. -i = Ask before updating a file or directory that exists in the destination with the same name. -r = To copy a directory including its contents to a new directory, recursive. CRONTAB Scheduled files crontab filename [-r][-l][-e] pathname The crontab command allows you to run, delete or edit scheduled tasks. -l = lists your currently scheduled tasks. -r = deletes all currently scheduled tasks. -e = edit your scheduled tasks. DATE List current date and time date DF Disk space info df [-k] [filesystem] Shows disk space available on the system. -k = Use 1024 byte blocks instead of the default 512. filesystem = If omitted displays the amount of disk space used and available on all mounted filesystems. DU Disk space info du [-aks] [filename | directoryname] Shows how much disk space is being used up by folders. -a = Shows counts for all files encountered, not only directories. -k = Use 1024 byte blocks instead of the default 512. -s = Don't display space usage of subdirectories. DIFF Display the differences between two text files diff textfile1 textfile2 ECHO Output string echo characterstring Displays the character string to the standard output device. EXIT Exit system exit Exit the system or logout. FG Execute processes in the foreground fg [%n] %n = Without this parameter it restarts the job that is currently executed in the background. With a number the process with the given number is restarted in the foreground. & = At the end of a command starts the process in the foreground. FILE File classification file filename(s) Shows information about the file type of the filename(s). FIND Search command find directorypath(s) searchpattern action(s) Search the specified directorie(s) for files that satisfy the search pattern and act on them according to the action(s) parameter. Search-patterns -name filename = search for files with the specified filename. - size n = search for files of n blocks (usually 512 or 1024 bytes). - links n = search for files with n links. - atime n = search for files that have been last accessed before n days. - mtime n = search for files that have been last modified before n days. - newer filename = search for files that have been modified more recently than the specified file. Actions - print = display the path(s) of the files found. - exec command = run command for each file found - ok command = as exec, but it asks for approval before the action. Notes Search patterns can be combined. ! = negation -o = logical OR One or more search patterns are combined using logical AND. ( ) or \ \ = these can be used to define groups of search patterns. FINGER User info finger emailaddress Shows more information about a user. FTP FTP to a site ftp hostname (or IP address) Connects to a FTP site. GCC Compile source code gcc option filename Compile source code into a file. GOPHER Connect to Gopher gopher Use the Gopher database browser. GREP Search in a file grep [-c,-n,-i,-v,-w,-y] pattern [filename(s)] Search for a string in a file or files. -c = displays only the number of lines that match. -n = displays the line number in front of every displayed line. -i = ignore case. -v = displays all other lines except those lines that match. -w = matches whole words only. -y = case independent pattern matching, lower case letters in pattern will also match upper case letters in the input. GZIP Compress a file gzip filename Compress a file. HEAD Display head of a file head [-n] filename(s) Display the first n lines of the named file(s). If no number is given the first 10 lines are displayed. -n = the number of lines to display from the top of the file. HOSTNAME Display hostname hostname Display the name of the host machine. IRC Connect to IRC irc hostname (or IP address) Connect to an Internet Relay Chat host. JOBS Display active processes jobs KILL Terminate process kill [-signr] process_ID Terminate the process with the specified process ID. -9 = send a definite kill signal. LOGOUT Logs off the system logout lprint Print a file lprintd Abort a print job lprintq List the print queue LS List files in the current directory ls [-CFRR*acdglrstu] [list of filenames or directories] The -a switch will include hidden files (hidden files in UNIX begin with a dot (.)), the current directory and parent directory entries (. and .. respectively). You can combine switches by placing them one after the other (ls -la, etc..) -C = list entries in columns. -F = list directories with /. -R = list subdirectories as well. -R* = list subdirectories 2 levels below current directory. -a = list all entries, including files with a dot (.htaccess, etc..). -c = sort entries by last modified date. -d = list directories only. -g = list hidden files and directories. -l = list in long format (mode, no of links, owner, group, size, and modified date). -r = list in reverse order. -s = list size in 1024 byte blocks. -t = sort contents by time of last modified date. -u = use time of last access (not last modified date) for sorting (with -t) or printing onscreen (with -l). MAKE Compile source code make command Compile a source code. MAKEFILE Compile source code file make filename Compile a source code into a file. MAN Read the help man command Shows the help on the entered command, f.e. man ls, man chmod, etc. To search for some text, press the forward-slash (/) key and type the text you want to search for. If you want to run a program that's in your current directory, you'll need to put a dot-slash (./) in front of the program name. MKDIR Create a directory mkdir directoryname, mkdir -i directoryname To create a directory in the current directory, type mkdir followed by the directory name. To delete a directory and all its contents, use rm -r directoryname. The -i parameter will make the system prompt you before deleting a file or directory. If the directory is empty, you can also delete it using the rmdir command. MORE List a file more filename View a file with a pause after every full screen. MV Rename a file mv oldname newname PASSWORD Change password password Change the administrator password. PICO Edit a file pico filename An easy to use text editor. PINE A mailer program pine An easy to use mailer program. PWD What is the current directory pwd RM Delete/remove a file rm filename To delete a single file, use rm filename. RMDIR Remove a directory rmdir directoryname, rm -r directoryname ( to delete folders with its files). RZ Receive a file rz Receive a file using Zmodem. SZ Send a file sz filename Send a file using Zmodem. TAIL Show last lines of a file tail filename Show the last few lines of a file. TALK Page user to chat talk username Pages the user for a chat, the user is an e-mail address. TAR Archive files tar filename Create or extract multiple file archives. Other methods are lharc, lzh, and lha, but these methods may not be present on your system. TIN, TRN Connect to Usenet tin, trn Connect to Usenet newsgroups. TELNET Connect telnet hostname (or IP address) Connect to an Internet web site. DOS2UNIX Conversion of text files dos2unix filename newname Strips the carriage returns (CR) from the DOS text file. UNIX2DOS Conversion of text files unix2dos filename newname Adds the carriage returns (CR) to the Unix text file. WHO Who is logged in? who Shows who is logged into the local system. W Who is logged in and what are they doing? w Shows who is logged into the local system and what they are doing. WRITE Write to a user write username Write to a user on the local system (CTRL-C to end it). ZIP Compress to zip zip username Compress to zip for IBM files.