basic shell commands

Created at 2014-06-25 Updated at 2024-11-07 - 8 min. read Category work Tag shell / terminal / ubuntu

• cat - Send a file to the screen in one go. Useful for piping to other programs
  cat file1 # list file1 to screen
  cat file1 file2 file3 > outfile # add files together into outfile
  cat *.txt > outfile # add all .txt files together
  cat file1 file2 | grep fred # pipe files

• cc - Compile a C program
  cc test1.c # compile test1.c to a.out
  cc -O2 -o test2.prog test2.c # compile test2.c to test2.prog

• cd - Change current directory
  cd # go to home directory
  cd ~/papers # go to /home/user/papers
  cd ~fred # go to /home/fred
  cd dir # go to directory (relative)
  cd /dir1/dir2/dir3… # go to directory (absolute)
  cd - # go to last directory you were in

• cp - Copy file(s)
  cp file1 file2 # copy file1 to file2
  cp file1 directory # copy file1 into directory
  cp file1 file2 file3 … directory # copy files into directory
  cp -R dir1 dir2/ # copy dir1 into dir2 including subdirectries
  cp -pR dir1 dir2/ # copy directory, preserving permissions

• date - Shows current date
   

• emacs - The ubiquitous text editor
  emacs foo.txt # open file in emacs

• file - Tells you what sort of file it is
  > file temp_70.jpg
  temp_70.jpg: JPEG image data, JFIF standard 1.01,
  resolution (DPI), 72 x 72

• firefox - Start Mozilla Firefox
   

• gedit - Gnome text editor
   

• grep - Look for text in files. List out lines containing text (with filename if more than one file examined).
  grep “hi there” file1 file2 … # look for ‘hi there’ in files
  grep -i “hi there” filename # ignore capitals in search
  cat filename | grep “hi there” # use pipe
  grep -v “foo” filename # list lines that do not include foo

• gtar - GNU version of the tar utility (also called tar on Linux). Store directories and files together into a single archive file. Use the normal tar program to backup files to a tape. See info tar for documentation.
  gtar cf out.tar dir1 # put contents of directory into out.tar
  gtar czf out.tar.gz dir1 # write compressed tar, out.tar.gz
  gtar tf in.tar # list contents of in.tar
  gtar tzf in.tar.gz # list contents of compressed in.tar.gz
  gtar xf in.tar # extract contents of in.tar here
  gtar xzf in.tar.gz # extract compressed in.tar.gz
  gtar xf in.tar file.txt … # extract file.txt from in.tar

• gzip / gunzip - GNU Compress files into a smaller space, or decompress .Z or .gz files.
  gzip file.fits # compresses file.fits into file.fits.gz
  gunzip file.fits.gz # recovers original file.fits
  gzip .dat # compresses all .dat files into .dat.gz
  gunzip .dat.gz # decompresses all .dat.gz files into .dat
  program | gzip > out.gz # compresses program output into out.gz
  program | gunzip > out # decompresses compressed program output

• info - A documentation system designed to replace man for GNU programs (e.g. gtar, gcc). Use cursor keys and return to go to sections. Press b to go back to previous section. A little hard to use.
  info gtar # documentation for gtar

• kill - Kill, pause or continue a process. Can also be used for killing daemons.
  > ps -u jss
  …
  666 pts/1 06:06:06 badprocess
  > kill 666 # this sends a nice’’ kill to the

  process. If that doesn’t work do

  > kill -KILL 666 # (or equivalently)
  > kill -9 666 # which should really kill it!

> kill -STOP 667 # pause (stop) process
> kill -CONT 667 # unpause process

• latex - Convert a tex file to dvi
   

• logout - Closes the current shell. Also try exit’’.
   

• lp - Sends files to a printer
  lp file.ps # sends postscript file to the default printer
  lp -dlp2 file.ps # sends file to the printer lp2
  lp -c file.ps # copies file first, so you can delete it
  lpstat -p lp2 # get status and list of jobs on lp2
  cancel lp2-258 # cancel print job lp2-258

lpr -Plp2 file.ps # send file.ps to lp2
lpq -Plp2 # get list of jobs on lp2
lprm -Plp2 1234 # delete job 1234 on lp2

• ls - Show lists of files or information on the files
  ls file # does the file exist?
  ls -l file # show information about the file
  ls *.txt # show all files ending in .txt
  ls -lt # show information about all files in date order
  ls -lrt # above reversed in order
  ls -a # show all files including hidden files
  ls dir # show contents of directory
  ls -d dir # does the directory exist?
  ls -p # adds meaning characters to ends of filenames
  ls -R # show files also in subdirectories of directory
  ls -1 # show one file per line

• man - Get instructions for a particular Unix command or a bit of Unix. Use space to get next page and q to exit.
  man man # get help on man
  man grep # get help on grep
  man -s1 sort # show documentation on sort in section 1

• more - Show a file one screen at a time
  more file # show file one screen at a time
  grep ‘frog’ file | more # Do it to output of other command

• mv - Move file(s) or rename a file
  mv file1 file2 # rename file1 to file2
  mv dir1 dir2 # rename directory dir1 to dir2
  mv file1 file2 file3 … directory # move files into directory

• nano - very simple text editor. Warning - this program can introduce extra line breaks in your file if the screen is too narrow!
   

• nice - Start a process in a nice way. Nice levels run from -19 (high priority) to 19 (low priority). Jobs with a higher priority get more CPU time. See renice for more detail. You should probably be using the grid-engine to run long jobs.
  nice +19 myjob1 # run at lowest priority
  nice +8 myjob2 # run at lowish priority

• openoffice.org - a free office suite available for Linux/Unix, Windows and Mac OS X.
   

• passwd - change your password
   

• pine - A commonly used text-based mail client. It is now called alpine. Allows you to send and receive emails. Configuration options allow it to become quite powerful. Other alternatives for mail are mozilla mail and mutt, however I suggest you stick to alpine or thunderbird.
   

• printenv - Print an environment variable in tcsh
  setenv MYVARIABLE Fred
  printenv MYVARIABLE
  printenv # print all variables

• ps - List processes on system
  > ps -u jss # list jss’s processes
  934 pts/0 00:00:00 bash

PID output CPU time name
> ps -f # list processes started here in full format
> ps -AF # list all processes in extra full format
> ps -A -l # list all processes in long format
> ps -A | grep tcsh # list all tcsh processes

• pwd - Show current working directory
  > pwd
  /home/ashu/writing/lecture

• quota - Shows you how much disk space you have left
  > quota -v
  …

• rm - Delete (remove) files
  rm file1 # delete a file (use -i to ask whether sure)
  rm -r dir1 # delete a directory and everything in it (CARE!)
  rm -rf dir1 # like above, but don’t ask if we have a -i alias

rmdir - Delete a directory if it is empty (rm -r dirname is useful if it is not empty)

rmdir dirname

• top - Interactively show you the top'' processes on a system - the ones consuming the most computing (CPU) time. Press theq’’ key in top to exit. Press the k'' key to kill a particular process. Pressr’’ to renice a process.