在perl中连接字符串时出现意外结果

Question

I am trying to execute below script but not getting desired output. it seems like it is still preserving old value and keep concatenating it.

./test.pl -v v10,v11,v12

Actual Result => 'v10','v11','v10','v12','v10','v11','v10'

Expected Result => 'v10','v11','v12'

can you please help resolve the issue?

#!/usr/bin/perl

use strict;
use warnings;
use Getopt::Long;

my ($versionFlag,$finalVersionList);

sub validateInputAndFilter
{
        my ($passedVersionList) = @_;
        $finalVersionList ="";

        my @versionList = split(",",$passedVersionList);
        foreach my $ver (@versionList)
        {
                if($ver =~ m/^v[0-9][0-9]$/)
                {
                        $finalVersionList .= "'$ver',$finalVersionList";
                }
                else
                {
                        print "\nWARNING: Passed version *** $ver *** is NOT in expected format...skipping...\n";
                }
        }
        $finalVersionList =~ s/\,$//;
        print "\n\nfinalVersionList => $finalVersionList\n\n";
}

GetOptions('v|version=s' => \$versionFlag) || die "Please pass version list separated by comma";

if(defined $versionFlag)
{
        &validateInputAndFilter("$versionFlag");
}
else
{
        die "Please pass version list separated by comma";
}
exit 0;

Answer 1

This:

$finalVersionList .= "'$ver',$finalVersionList";

Should just be :

$finalVersionList .= "'$ver,'";

$foo .= $bar ; is equivalent to :

$foo = $foo . $bar;

So, $finalVersionList .= "'$ver',$finalVerionList"; is equivalent to :

$finalVersionList = $finalVersionList . "'$ver',$finalVersionList";

Answer 2

Change:

 $finalVersionList .= "'$ver',$finalVersionList";

To:

 $finalVersionList .= "'$ver',";

You're doing multiple appends here. What you had originally is equivalent to:

 $finalVersionList = $finalVersionList . "'$ver',$finalVersionList";

Which is not what you want. If you want '$ver$', to be at the fromt of the list, you could do:

$finalVersionList = "'$ver'," . $finalVersionList;

or:

 $finalVersionList = "'$ver',$finalVersionList";