Decoding a regular expression in Perl

Question

I am trying to decode the following Perl regular expression:

$fname =~ /\/([^\/]+)\.txt$/

What are we trying to match for here?

Answer 1

\/([^\/]+)\.txt

This regular expression matches a file name, as it exists in a path

• Minus the extension, and
• Only when (or starting where) the path begins with an up-right slash.

Examples:

\folder\path\file.txt

Nothing is matched.

folder/path/file.txt

file.txt is matched (and file is placed in capture group 1: $1).

/folder/path/file.txt

Again, file.txt is matched (and file captured).

You can try it yourself at Debuggex

Answer 2

Here's how you break it down.

• \/ - the literal character /
• (...) - followed by a group that will be captured to $1
  • [ ... ] - a character class
    • ^ - in a character class, this means take the inversion of the specified set
    • \/ - the literal character /
  • + - one or more times
• \. - the literal character .
• txt - the literal string txt
• $ - the end of the string

So, in other words, this is trying to match "anything with a / followed by one or more characters that are not /, followed by .txt, followed by the end of the string, and put the part before .txt into $1"