perl: increment variable inside string interpolation

Question

Is it possible to use the ++ operator inside a string interpolation? I've attempted the following:

my $i = 0;
foreach my $line (@lines) {
    print "${i++}. $line\n";
}

but I get Compile error: Can't modify constant item in postincrement (++)

Answer 1

You can use ${\($var++)} to increment the variable while interpolating it.

use strict ;
use warnings ;

my $var = 5 ;

print "Before:     var=$var\n" ;
print "Incremented var=${\($var++)}\n" ;
print "After:      var=$var\n" ;

This will print

Before:     var=5
Incremented var=6
After:      var=6

But I would suggest as mentioned in the comments not to use this code because using printf is easier to write and read.