#! perl -slw
use strict;

my @regex = (
    qr[Error 123 on (\S+) file not found error],
    qr[Error 124 on (\S+):(\S+) no space left],
);

while( <DATA> ) {
    chomp;
    for my $regex ( @regex ) {
        print "'$_' ", ( $_ =~ $regex ? 'does    ' : 'does not' )," match $regex";
    }
}

__DATA__
Error 123 on SystemA file not found error
Error 123 on SystemB file not found error
Error 123 on SystemC file not found error
Error 124 on User1:FileA no space left
Error 124 on User2:FileB no space left
Error 124 on User3:FileC no space left

##</code><code>##

c:\test>junk9
'Error 123 on SystemA file not found error' does     match (?-xism:Error 123 on (\S+) file not found error)
'Error 123 on SystemA file not found error' does not match (?-xism:Error 124 on (\S+):(\S+) no space left)
'Error 123 on SystemB file not found error' does     match (?-xism:Error 123 on (\S+) file not found error)
'Error 123 on SystemB file not found error' does not match (?-xism:Error 124 on (\S+):(\S+) no space left)
'Error 123 on SystemC file not found error' does     match (?-xism:Error 123 on (\S+) file not found error)
'Error 123 on SystemC file not found error' does not match (?-xism:Error 124 on (\S+):(\S+) no space left)
'Error 124 on User1:FileA no space left' does not match (?-xism:Error 123 on (\S+) file not found error)
'Error 124 on User1:FileA no space left' does     match (?-xism:Error 124 on (\S+):(\S+) no space left)
'Error 124 on User2:FileB no space left' does not match (?-xism:Error 123 on (\S+) file not found error)
'Error 124 on User2:FileB no space left' does     match (?-xism:Error 124 on (\S+):(\S+) no space left)
'Error 124 on User3:FileC no space left' does not match (?-xism:Error 123 on (\S+) file not found error)
'Error 124 on User3:FileC no space left' does     match (?-xism:Error 124 on (\S+):(\S+) no space left)