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6.1. Copying and Substituting Simultaneously
6.1.1. Problem
You're tired of using two separate
statements with redundant information, one to copy and another to
substitute.
6.1.2. Solution
Instead of:$dst = $src;
$dst =~ s/this/that/;
use:($dst = $src) =~ s/this/that/;
6.1.3. Discussion
Sometimes you wish you could run a search and replace on a copy of a
string, but you don't care to write this in two separate steps. You
don't have to, because you can apply the regex operation to the
result of the copy operation.For example:# strip to basename
($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 = $manpage) =~ s/man(?=\d)/cat/;
You can even use this technique on an entire array:@bindirs = qw( /usr/bin /bin /usr/local/bin );
for (@libdirs = @bindirs) { s/bin/lib/ }
print "@libdirs\n";
/usr/lib /lib /usr/local/lib
Because
of precedence, parentheses are required when combining an assignment
if you wish to change the result in the leftmost variable. The result
of a substitution is its success: either " for
failure, or an integer number of times the substitution was done.
Contrast this with the preceding examples where the parentheses
surround the assignment itself. For example:($a = $b) =~ s/x/y/g; # 1: copy $b and then change $a
$a = ($b =~ s/x/y/g); # 2: change $b, count goes in $a
$a = $b =~ s/x/y/g; # 3: same as 2
6.1.4. See Also
The "Variables" section of Chapter 2 of Programming
Perl, and the "Assignment Operators" section of
perlop(1) and Chapter 3 of
Programming Perl
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| 6. Pattern Matching |  | 6.2. Matching Letters |
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