## 36.8. Save Disk Space and Programming: Multiple Names for a Program

If you're writing:

- several programs that do the same kinds of things,

- programs that use a lot of the same code (as you're writing the second, third, etc., programs, you copy a lot of lines from the first program), or

- a program with several options that make big changes in the way it works,

you might want to write just one program and make links (Section 10.4, Section 10.3) to it instead. The program can find the name you called it with and, through case or test commands, work in different ways. For instance, the Berkeley Unix commands ex, vi, view, edit, and others are all links to the same executable file. This takes less disk space and makes maintenance easier. It's usually sensible only when most of the code is the same in each program. If the program is full of name tests and lots of separate code, this technique may be more trouble than it's worth.

Depending on how the script program is called, this name can be a simple relative pathname like `prog` or `./prog` -- it can also be an absolute pathname like `/usr/joe/bin/prog` (Section 31.2 explains pathnames). There are a couple of ways to handle this in a shell script. If there's just one main piece of code in the script, as in the lf script, a case that tests `$0` might be best. The asterisk (`*`) wildcard at the start of each case (see Section 35.11) handles the different pathnames that might be used to call the script:

>     case "$0" in
>     *name1)
>         ...do this when called as name1...
>         ;;
>     *name2)
>         ...do this when called as name2...
>         ;;
>         ...
>     *)  ...print error and exit if $0 doesn't match...
>         ;;
>     esac

You might also want to use basename (Section 36.13) to strip off any leading pathname and store the cleaned-up `$0` in a variable called myname. You can test `$myname` anywhere in the script and also use it for error messages:

>     myname=`basename $0`
>        ...
>     case "$myname" in
>        ...

>     echo "$myname: aborting; error in xxxxxx" 1>&2
>        ...

-- JP

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