PERL regex modifiers for m//

[rockstar99]

Could someone please give an example of 'm / / m' related example and compare to 'm / / s' example. Thanks in advance.

[moritz]

I'm pretty sure that "Mastering Regular Expressions" by Jeffrey Friedl has extensive examples, and perlretut also has some; just search for "modifier" in the documnent.

[Stamm]

$s = "foo\nfoot\nroot";
$s =~ /^foo/g;           # matches only the first foo
$s =~ /^foo/gm;          # matches both foo
$s =~ /f.*t/g;           # matches only foot
$s =~ /f.*t/gs;          # matches foo\nfoot\nroot
$s =~ /f.*?t/gs;         # matches foo\nfoot
$s =~ /^foot.*root$/g;   # doesn't match
$s =~ /^foot.*root$/gm;  # doesn't match
$s =~ /^foot.*root$/gs;  # doesn't match
$s =~ /^foot.*root$/gms; # matches foot\nroot

[ww]

Line 3: " # matches both foo": are you sure?

C:>perl -e "$s = \"foo\nfoot\nroot\";($y) = $s =~ /^foo/gm;print $y;"
foo

[ikegami]

Yes, but not in the same pass.

>perl -E"say join ',', qq{foo\nfoot\nroot} =~ /^foo/gm;"
foo,foo

[Corion]

What part of the first section of perlre, ("Modifiers") , do you have problems with?

[Khen1950fx]

See: Regexp_Quote_Like_Operators.

[Anonymous Monk]

http://perldoc.perl.org/perlre.html#Modifiers

I'm sorry that I cannot make this a hyper-link, but the site admins recently prohibited posting external links as Anonymonk.

[Anonymous Monk]

Yes we can

[remiah]

As for s and m switch, example of "little princess" in this node was very nice tutorial for me.

[ikegami]

"m" affects "^" and "$".

"s" affects "."

How can one compare two independent things?

[educated_foo]

How can one compare two independent things?

It's not so hard:
• //m causes ^ and $ to match at newlines in the middle of your string, while //s causes . to match newlines.
• The Nile is a river in Africa, while the Mississippi is a river in North America.
• The -g flag turns on debugging information, while the -O flag turns on optimization.

[ikegami]

//m causes ^ and $ to match at newlines in the middle of your string, while //s causes . to match newlines.

You're comparing using /m to not using /m, and using /s to not using /s. You're not comparing /m to /s.

Your river example compares the location of the rivers, but there's no common aspect of /m and /s to compare.

[ikegami]

//m causes ^ and $ to match at newlines in the middle of your string, while //s causes . to match newlines.

You're comparing using /m to not using /m, and using /s to not using /s. You're not comparing /m to /s.

Your river example compares the location of the rivers, but there's no common aspect of /m and /s to compare.

[TJPride]

I often get confused as to which is which myself. I generally try both and then pick the one that works the way I want it to.

[AnomalousMonk]

I often get confused as to which is which myself.

This is the point of TheDamian's injunctions in Perl Best Practices (PBP) to always use the /m and /s (and /x) modifiers (BPs 148 and 151 – and 147) in every match and regex object definition:  . ^ $ always behave the same way and confusion is at least reduced if not eliminated.

[BrowserUk]

Hm. That's like advocating always taking a swimsuit & sunblock and a raincoat & umbrella cos it saves listening to the weather forecast. More than slightly ridiculous.

The very reason it is hard, even for long-time Perlers with scads of frequent regex user miles, to remember which (/s /m) does what, is because they are so rarely required.

So what could possibly be wrong with advocating their use at all times?

For a start, you're crying wolf. By using them everywhere they become the norm, and after a while people stop asking themselves why is he using that here. And that is bad.