Passing a regex substitution as a variable in Perl?

Question

I need to pass a regex substitution as a variable:

sub proc {
    my $pattern = shift;
    my $txt = \"foo baz\";

    $txt =~ $pattern;
}

my $pattern = \'s         


        

Answer 1

I have an extremely simple script for mass file renaming that employs this trick :

#!/opt/local/bin/perl
sub oops { die "Usage : sednames s/old/new [files ..]\n"; }
oops if ($#ARGV < 0);

$regex = eval 'sub { $_ = $_[0]; ' . shift(@ARGV) . '; return $_; }';
sub regex_rename { foreach (<$_[0]>) {
    rename("$_", &$regex($_));
} }

if ($#ARGV < 0) {  regex_rename("*");  }
else {  regex_rename(@ARGV);  }

Any perl command that modifies $_ like s/old/new could be employed to modify the files.

I decided upon using eval so that the regular expression only needed to be compiled once. There is some wonkiness with eval and $_ that prevented me from using simply :

eval 'sub { ' . shift(@ARGV) . ' }';

although this &$regex certainly does modify $_; requiring the "$_" to evaluate $_ before calling rename. Yes, eval is quite fragile, like everyone else said.

Answer 2

You're right - you were very close:

eval('$txt =~ ' . "$pattern;");

Answer 3

I found a probably better way to do it:

sub proc {
    my ($pattern, $replacement) = @_;
    my $txt = "foo baz";

    $txt =~ s/$pattern/$replacement/g;  # This substitution is global.
}

my $pattern = qr/foo/;  # qr means the regex is pre-compiled.
my $replacement = 'bar';

proc($pattern, $replacement);

If the flags of the substitution have to be variable, you can use this:

sub proc {
    my ($pattern, $replacement, $flags) = @_;
    my $txt = "foo baz";

    eval('$txt =~ s/$pattern/$replacement/' . $flags);
}

proc(qr/foo/, 'bar', 'g');

Please note that you don't need to escape / in the replacement string.