Runtime Error "Can't modify non-lvalue subroutine"

Question

I have an array @jobs that contains 1 or more strings, but when I run the following code I get a runtime error "Can't modify non-lvalue subroutine call at /home/xa341d/bin/hourly.pl line 32"

elsif (@jobs > 0) {
    my $my_jobs = "";
    my $i;

   for ($i = 0; i <= $#jobs; i++) {
       my $temp = $jobs[$i];
       $my_jobs += "-j $temp ";
   }

   print "my_jobs = $my_jobs\n";
    open $alOut, "/home/zn035b/bin/autorep2.pl $my_jobs -l 0 | grep `date \"+%m/%d/%Y\"` | sort -k 3,3|" or die "Can't open: $!";
}

does anyone know what might be going on here?

Answer 1

A Perl programmer would write that foreach loop as:

foreach my $job (@jobs) {
  $my_jobs .= "-j $job ";
}

Or perhaps:

$my_jobs .= "-j $_ " foreach @jobs;

C-style for loops are rarely used in Perl. And for good reason. A foreach loop is usually far easily to understand.

You could also do it with map:

my $jobs = join ' ', map { "-j $_" } @jobs;

Answer 2

Add this to the top of the script.

use warnings;
use strict;

You'll see that you're using i instead of $i in the loop, and also += instead of .= which should be used for concatenation. +=, on the other hand, adds numeric value of the right side (which is 0, since "-j" is not a number) to the left side.

That said, I failed to get the "non-lvalue sub" message out of this code so you probably should provide more info or at least tell us what line 32 is.