'multiline' or 'single string' in regex?

[AMiSM]

Hi, folks!
In a substitution regex, when would you use the 'm' option, and when would you use the 's' option?

 

[KevinADC]

'm' is for if you want the regexp to evaluate each line in a string:

my $string = q~mary had a little lamb
it's fleece was white as snow
everywhere that mary went
the lamb was sure to go~;

$string =~ s/^/foo/mg;

print $string;

prints:

foomary had a little lamb
fooit's fleece was white as snow
fooeverywhere that marry went
foothe lamb was sure to go


's' treats the entire string as one line:

my $string = q~mary had a little lamb
it's fleece was white as snow
everywhere that marry went
the lamb was sure to go~;

$string =~ s/^/foo/sg;

print $string;

prints:

foomary had a little lamb
it's fleece was white as snow
everywhere that marry went
the lamb was sure to go

 

[AMiSM]

ok.
thanks!