How do I substitute with an evaluated expression in Perl?

Question

There\'s a file dummy.txt

The contents are:

 9/0/2010
 9/2/2010
 10/11/2010

I have to change the month portion (0,2,11) to +1, ie, (1,3

Answer 1

this works: (e is to evaluate the replacement string: see the perlrequick documentation).

$line = '8/10/2010';
$line =~ s!/(\d+)/!('/'.($1+1).'/')!e;

print $line;

It helps to use ! or some other character as the delimiter if your regular expression has / itself.

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You can also use, from this question in Can Perl string interpolation perform any expression evaluation?

$line = '8/10/2010';
$line =~ s!/(\d+)/!("/@{[$1+1]}/")!e;

print $line;

but if this is a homework question, be ready to explain when the teacher asks you how you reach this solution.