cryptic perl expression

I find the following statement in a perl (actually PDL) program:


Can someone decode this for me, an apprentice in perl programming?


Sure, I'll explain it from the inside out:

\w - matches a single character that can be used in a word (alphanumeric, plus '_')

[...] - matches a single character from within the brackets

[\w] - matches a single character that can be used in a word (kinda redundant here)

+ - matches the previous character, repeating as many times as possible, but must appear at least once.

[\w]+ - matches a group of word characters, many times over. This will find a word.

(...) - grouping. remember this set of characters for later.

([\w]+) - match a word, and remember it for later

$ - end-of-line. match something at the end of a line

([\w]+)$ - match the last word on a line, and remember it for later

\/ - a single slash character '/'. it must be escaped by backslash, because slash is special.

\/([\w]+)$ - match the last word on a line, after a slash '/', and remember the word for later. This is probably grabbing the directory/file name from a path.

/.../ - match syntax

/.../i - i means case-insensitive.

All together now:

/\/([\w]+)$/i; - match the last word on a line and remember it for later; the word must come after a slash. Basically, grab the filename from an absolute path. The case insensitive part is irrelevant, \w will already match both cases.

More details about Perl regex here:

And as JRFerguson pointed out, YAPE::Regex::Explain is useful for tokenizing regex, and explaining the pieces.

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