I have an installation script which behaviour differs undesired depending of prior execution of unrelated regex.

The script restarts services after completing the installation, but when

$supported =~ /\Q4.1.2/

is not executed not all services are started.

I have absolutely no clue as to why not executing an otherwise unrelated regex changes the behaviour of regexs inside a function called later.

Is this behaviour caused by using an undefined variable in a regex?

It looks mighty strange and I have worked around the issue by not using an undefined variable in a regex

I have reduced the installation script to

use v5.30.0;

my @stoppedGeneralServices = ( 'OP Mover', 'OP Monitor');
my @stoppedStandardServices = ( 'OP OPC Client', 'OP Calculation Serve
+r', 'OP Data Server', 'OP Configuration Server', 'OP Log Server', 'OP
+ Time Server', 'ONC RPC PortMapper');

my $supported = '4.0.0,4.0.1,4.1.0,4.1.1,4.1.2';

$supported =~ /\Q4.1.2/ if @ARGV;

say "Start Basic Standard Services:";
startStandardServices( 'Config');
say "Start Remaining Standard Services:";
startStandardServices();
say "Start General Services:";
startGeneralServices();

say "Installation completed";

sub startStandardServices {
    my $last = shift;
    my $name;
    while (@stoppedStandardServices) {
        $name = pop @stoppedStandardServices;
        say '  Starting $name=\'', $name, '\' $last=', defined $last ?
+ "'$last'" : 'undef', ' ($name=~/$last/i)=', ($name =~ /$last/i) ? 1 
+: 0;
        last if $name =~ /$last/i;
    }
}

sub startGeneralServices {
    my $last = shift;
    my $name;
    while (@stoppedGeneralServices) {
        $name = pop @stoppedGeneralServices;
        say '  Starting $name=\'', $name, '\' $last=', defined $last ?
+ "'$last'" : 'undef', ' ($name=~/$last/i)=', ($name =~ /$last/i) ? 1 
+: 0;
        last if $name =~ /$last/i;
    }
}

[download]

When executed without arguments the output is:

D:\>surprise.pl
Start Basic Standard Services:
  Starting $name='ONC RPC PortMapper' $last='Config' ($name=~/$last/i)
+=0
  Starting $name='OP Time Server' $last='Config' ($name=~/$last/i)=0
  Starting $name='OP Log Server' $last='Config' ($name=~/$last/i)=0
  Starting $name='OP Configuration Server' $last='Config' ($name=~/$la
+st/i)=1
Start Remaining Standard Services:
  Starting $name='OP Data Server' $last=undef ($name=~/$last/i)=1
Start General Services:
  Starting $name='OP Monitor' $last=undef ($name=~/$last/i)=1
Installation completed

[download]

When executed with an argument the output is:

D:\>surprise.pl all
Start Basic Standard Services:
  Starting $name='ONC RPC PortMapper' $last='Config' ($name=~/$last/i)
+=0
  Starting $name='OP Time Server' $last='Config' ($name=~/$last/i)=0
  Starting $name='OP Log Server' $last='Config' ($name=~/$last/i)=0
  Starting $name='OP Configuration Server' $last='Config' ($name=~/$la
+st/i)=1
Start Remaining Standard Services:
  Starting $name='OP Data Server' $last=undef ($name=~/$last/i)=0
  Starting $name='OP Calculation Server' $last=undef ($name=~/$last/i)
+=0
  Starting $name='OP OPC Client' $last=undef ($name=~/$last/i)=0
Start General Services:
  Starting $name='OP Monitor' $last=undef ($name=~/$last/i)=0
  Starting $name='OP Mover' $last=undef ($name=~/$last/i)=0
Installation completed

[download]

In reply to Side effect of using undefined variable in regex by Anonymous Monk

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