Question

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

/\/([\w]+)$/i;

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

Answer 1

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: http://www.troubleshooters.com/codecorn/littperl/perlreg.htm

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