What is the "$0 =~ s!.*/!!" meaning in perl?

Question

I want to know the meaning of

    "$0 =~ s!.*/!!"  

in perl , and how can I learn this grammer ？ Welcome all kinds of answers.

Answer 1

This truncates the name of the script ($0) to just its basename. It is useful for diagnostics. Without the truncation, your warning messages

warn "$0: Failed to mumble"

would come out as

weird/long/path/to/mumble.pl: Failed to mumble at line 3.

whereas with the truncation, it shows

mumble.pl: Failed to mumble at line 3.

So it's just a readability tweak for warning messages, really. But it's a common idiom.

The hard part for a beginner is probably the realization that s!foo!bar! is just another way to say s/foo/bar/. This is a godsend when you need to perform substitutions on strings which contain slashes. Without this syntactic sugar, you would need to backslash the slashes s/.*\/// which for a single slash isn't too ghastly, but it quickly leads to leaning toothpicks.