Shell Reference

Basic Commands

  • cat displays the contents of its inputs.
  • cd path changes the current working directory.
  • cp old new copies a file.
  • find finds files with specific properties that match patterns.
  • grep selects lines in files that match patterns.
  • head displays the first few lines of its input.
  • ls path prints a listing of a specific file or directory; ls on its own lists the current working directory.
  • man command displays the manual page for a given command.
  • mkdir path creates a new directory.
  • mv old new moves (renames) a file or directory.
  • pwd prints the user's current working directory.
  • rm path removes (deletes) a file.
  • rmdir path removes (deletes) an empty directory.
  • sort sorts its inputs.
  • tail displays the last few lines of its input.
  • touch path creates an empty file if it doesn't already exist.
  • wc counts lines, words, and characters in its inputs.
  • whoami shows the user's current identity.


  • /path/from/root is an absolute path.
  • / on its own refers to the root of the filesystem.
  • path/without/leading/slash is a relative path.
  • . refers to the current directory, .. to its parent.
  • * matches zero or more characters in a filename, so *.txt matches all files ending in .txt.
  • ? matches any single character in a filename, so ?.txt matches a.txt but not any.txt.

Combining Commands

  • command > file redirects a command's output to a file.
  • first | second connects the output of the first command to the input of the second.
  • A for loop repeats commands once for every thing in a list:

    for variable in name_1 name_2 name_3
        ...commands refering to $variable...
  • Use $name to expand a variable (i.e., get its value).
  • history displays recent commands, and !number to repeat a command by number.
  • bash filename runs commands saved in filename.
  • $* refers to all of a shell script's command-line parameters.
  • $1, $2, etc., refer to specified command-line parameters.
  • $(command) inserts a command's output in place.