How to make shell scripts robust to source being changed as they run

Question

Have people noticed that if you modify the source of a shell script, any instances that are currently running are liable to fail?

This in my opinion is very bad; it means that I have to make sure all instances of a script are stopped before I make changes. My preferred behavior would be that existing scripts continue running with old source code and that new instances use the new code (e.g. what happens for perl and python programs).

Do folks have any good workarounds for this behavior, other than pre-copying the shell script to a tempfile and running from that?

Thanks, /YGA

Answer 1

Very slight addition to the other answers:

#!/bin/sh
{
    # Your stuff goes here
    exit
}

The exit at the end is important. Otherwise, the script file might still be accessed at the end to see if there are any more lines to interpret.

This question was later reposted here: Can a shell script indicate that its lines be loaded into memory initially?

Answer 2

Make sure the shell has to parse the whole file before executing any of it:

#!/bin/ksh
{
all the original script here
}

That does the trick.

Incidentally, with Perl (and I assume Python), the program parses the entire file before executing any of it, exactly as recommended here. Which is why you don't usually run into the problem with Perl or Python.