44.22 Finding a Program Name; Multiple Program Names

A UNIX program should use its name as the first word in error messages it prints. That's important when the program is running in the background or as part of a pipeline - you need to know which program has the problem:

someprog

: quitting: can't read file xxxxxx

It's tempting to use just the program name in the echo commands:

echo "someprog

: quitting: can't read file $file" 1>&2

but if you ever change the program name, it's easy to forget to fix the messages. A better way is to store the program name in a shell variable at the top of the script file, and then use the variable in all messages:

myname=someprog


   ...
echo "$myname: quitting: can't read file $file" 1>&2

Even better, use the $0 parameter. The shell automatically puts the script's name there. But $0 can have the absolute pathname of the script, such as /xxx/yyy/bin/someprog . The basename (45.18 ) program fixes this: basename strips off the head of a pathname - everything but the filename.

For example, if $0 is /u/ehuser/bin/sendit , then:

myname="`basename $0`"

would put sendit into the myname shell variable.

Just as you can make links (18.3 ) to give UNIX files several names, you can use links to give your program several names (45.13 ) . For instance, see the script named ll , lf , lg (...and so on) in article 16.7 . Use $0 to get the current name of the program.