substitution - How to get the substituted text of perl (s//)? -

i use following code substitution. there way retrieve text substituted? in example, want string _5p_outsuffix.txt.

/tmp$ ./main.pl  xxx_5p_outsuffix.txt /tmp$ cat main.pl  #!/usr/bin/env perl  use strict; use warnings;  $filename="xxx_5p_insuffix.txt"; $insuffix="_((5|3)p)_insuffix\.txt"; $outsuffix = '_$1_outsuffix.txt';  $filename =~ s/$insuffix$/qq{"$outsuffix"}/ee; print "$filename\n"; 

you should capture match string:

$filename =~ s/($insuffix)$/qq{"$outsuffix"}/ee; print "$filename\n"; print "substituted: $1\n"; 

since introduces level of braces, have adjust numbers of captures used in replacement string. alternatively built-in ${^match} variable contains string matched last successful regex using /p modifier. like

$filename =~ s/$insuffix$/qq{"$outsuffix"}/eep; print "$filename\n"; print "substituted: ${^match}\n"; 

(you shouldn't use $& purpose makes regular expressions in program substantially slower.)