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.

Paths

• /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
  do
      ...commands refering to $variable...
  done
  

• 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.