Copying and Substituting Simultaneously

Problem

You're tired of constantly using two separate statements with redundant information, one to copy and another to substitute.

Solution

Instead of:

$dst = $src; $dst =~ s/this/that/;

use:

($dst = $src) =~ s/this/that/;

Discussion

Sometimes what you wish you could have is the new string, but you don't care to write it in two steps.

For example:

# strip to basename ($progname = $0) =~ s!^.*/!!; # Make All Words Title-Cased ($capword = $word) =~ s/(\w+)/\u\L$1/g; # /usr/man/man3/foo.1 changes to /usr/man/cat3/foo.1 ($catpage = $manpage) =~ s/man(?=\d)/cat/;

You can even use this technique on an entire array:

@bindirs = qw( /usr/bin /bin /usr/local/bin );
for (@libdirs = @bindirs) {
 s/bin/lib/
}
print "@libdirs\n"; /usr/lib /lib /usr/local/lib

The parentheses are required when combining an assignment if you wish to change the result in the leftmost variable. Normally, the result of a substitution is its success: either "" for failure, or the number of times the substitution was done. Contrast this with the preceding examples where the parentheses surround the assignment itself. For example:

($a = $b) =~ s/x/y/g; # copy $b and then change $a $a = ($b =~ s/x/y/g); # change $b, count goes in $a