Perl正则表达式：如何捕获管道文本中的组？

Question

I expected the output of

echo "(a b c)(a b c)" | perl -ne "/(a) b/g; print $1"

to be:

aa

since $1 refers to the first captured group, which happens to be "a".

However the above code outputs :

(a b c)(a b c)

What am I doing wrong?

Answer 1

First use single quotes under *nix, as this is not what you want:

echo "(a b c)(a b c)" | perl -MO=Deparse -ne "/(a) b/g; print $1"
LINE: while (defined($_ = <ARGV>)) {
  /(a) b/g;
  print $_;
}

and then use scalar context with /g to iterate over all matches

echo "(a b c)(a b c)" | perl -ne 'print $1 while /(a) b/g'

or use list context so regex returns all matches at once,

echo "(a b c)(a b c)" | perl -ne 'print /(a) b/g'