Use this tag for questions about options for shell commands: passing them and parsing them.

There are three common variants of option syntax; different commands use different syntax.

  • POSIX: This is the traditional Unix style. Options consists of a - (dash a.k.a. minus) followed by a single letter. If - is followed by multiple letters, each letter is an option (this is called bundling). Example: ls -la is equivalent to ls -l -a.
    An option can take an argument, which is either in the next word or glued to the option. Example: sort -st: is equivalent to sort -s -t :.
  • GNU: in addition to the POSIX syntax, options can start with -- and consist of multiple letters. Arguments are either given after a = or in the next word. Example: sort --stable --field-separator=: is equivalent to sort --stable --field-separator :.
  • Multi-letter: an option consists of a - followed by more characters (usually letters and dashes). If there is an argument, it is in the next word. Example: xterm -name foo -e foo

Further reading

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