10.9 Shell Functions

sh_init

The C shell has aliases (10.2 ) . But until System V Release 2, the Bourne Shell had almost (10.10 ) no way for users to set up their own built-in commands. Functions are like aliases, but better. For instance, functions can return a status (44.7 ) and have much more reasonable syntax (10.7 ) . bash and the Korn Shell have shell functions, too. To find out all about functions, check a shell programming book. There are examples in the sh_init file on the CD-ROM. Here are the examples from articles 10.2 and 10.3 changed into Bourne shell aliases:

• The la function includes "hidden" files in ls listings. The lf function labels the names as directories, executable files, and so on:

  la () { ls -a "$@"; }
  lf () { ls -F "$@"; }

  The spaces and the semicolon (; ) are both important! [3] The "$@" (44.15 ) is replaced by the command-line arguments (other options, or directory and filenames), if you use any:

  [3] A function is a Bourne shell list construct (13.8 ) . You can omit the semicolon in bash -but, if you do, your functions won't be portable.

  $ la -l somedir
  
              ...runs 
  ls -a -l somedir

• This next simple function, cur , gives the name of your current directory and then lists it:

  cur()
  {
      pwd
      ls
  }

That example shows how to write a function with more than one line. In that style, with the ending curly brace on its own line, you don't need a semicolon after the last command.