Get the name of the shell script from inside a function

Question

Say I've got this:

#!/bin/sh
function show_help {
  cat<<%
Usage: $0 [-h]
%
}
# the following lines is pseudo-code
if argument contains "-h"
  show_help
otherwise
  do_stuff

If I run ./test it does some stuff as intended, but if I run ./test -h, it produces

Usage: show_help [-h]

but I intended to let it produce

Usage: ./test [-h]

so how can I achieve this by modifying only the show_help function? I don't want to modify the script itself, so I won't just add SCRIPT_NAME=$0 under the shebang line.
I hope the solution is some kind of a builtin variable like $PWD or function like pwd, does there really exist one?

Answer 1

I can't reproduce this. The question is tagged with '/bash'.

With bash, $0 is always the name of the script, so if this is in /tmp/test

#!/bin/bash
function show_help {
cat <<%
Usage: $0 [-h]
%
}
show_help

then bash /tmp/test gives me Usage: /tmp/test [-h].

If I use ksh93 /tmp/test I do get Usage: show_help [-h], due to the ksh setting $0 when you declare a function in a non POSIX manner.

Switching to a portable function declaration

#!/bin/bash
show_help() {
cat <<%
Usage: $0 [-h]
%
}
show_help

and you get Usage: /tmp/test [-h] from both ksh and bash.

So there are multiple errors in the original script. The #!/bin/sh should be #!/bin/bash if the question is about bash, the function declaration is incorrect, and the syntax of the if at the end is just wrong.

Answer 2

In BASH, use $FUNCNAME[1]. $FUNCNAME[0] is the show_help. You an also get the line number in the parent function that called show_help as well as the name of the source file ($BASH_LINENO[1], $BASH_SOURCE[1]).

I am looking for a similar answer for korn shell (ksh)

Answer 3

Since this question seems to be homework question. So I am not answering in a exact way but putting some hints down.

1. Get the parent PID of running process from grep PPid /proc/self/status | awk '{print $2}
2. Find out it's executable name ls /proc/<PPid>/exe
3. Use readlink to print out the name of above softlink readlink /proc/<PPid>/exe

Output of 3 is the name of running script.