问题
I'm trying to work out how to match across newlines with perl (from the shell). following:
(echo a b c d e; echo f g h i j; echo l m n o p) | perl -pe 's/(c.*)/[$1]/'
I get this:
a b [c d e]
f g h i j
l m n o p
Which is what I expect. But when I place an /s at the end of my regex, I get this:
a b [c d e
]f g h i j
l m n o p
What I expect and want it to print is this:
a b [c d e
f g h i j
l m n o p
]
Is the problem with my regex somehow, or my perl invocation flags?
回答1:
-p loops over input line-by-line, where "lines" are separated by $/, the input record separator, which is a newline by default. If you want to slurp all of STDIN into $_ for matching, use -0777.
$ echo "a b c d e\nf g h i j\nl m n o p" | perl -pe 's/(c.*)/[$1]/s'
a b [c d e
]f g h i j
l m n o p
$ echo "a b c d e\nf g h i j\nl m n o p" | perl -0777pe 's/(c.*)/[$1]/s'
a b [c d e
f g h i j
l m n o p
]
See Command Switches in perlrun for information on both those flags. -l (dash-ell) will also be useful.
回答2:
The problem is that your one-liner works one line at a time, your regex is fine:
use strict;
use warnings;
use 5.014;
my $s = qq|a b c d e
f g h i j
l m n o p|;
$s =~ s/(c.*)/[$1]/s;
say $s;
回答3:
Actually your one-liner looks like this:
while (<>) {
$ =~ s/(c.*)/[$1]/s;
}
It's mean that regexp works only with first line of your input.
回答4:
There's More Than One Way To Do It: since you're reading "the entire file at a time" anyway, I'd personally drop the -p modifier, slurp the entire input explicitly, and go from there:
echo -e "a b c d e\nf g h i j\nl m n o p" | perl -e '$/ = undef; $_ = <>; s/(c.*)/[$1]/s; print;'
This solution does have more characters, but may be a bit more understandable for other readers (which will be you in three months time ;-D )
回答5:
You're reading a line at a time, so how do you think it can possibly match something that spans more than one line?
Add -0777 to redefine "line" to "file" (and don't forget to add /s to make . match newlines).
$ (echo a b c d e; echo f g h i j; echo l m n o p) | perl -0777pe's/(c.*)/[$1]/s'
a b [c d e
f g h i j
l m n o p
]
来源：https://stackoverflow.com/questions/13927672/how-do-i-match-across-newlines-in-a-perl-regex