Basic regex syntax, brackets create a character class

use re 'debug';
my $orig = 'my_stuff[1]=400';
my $want = 'my_stuff[1]=';


print "They Match\n" if  $orig =~ /$want/;
__END__
Compiling REx "my_stuff[1]="
Final program:
   1: EXACT <my_stuff1=> (8)
   8: END (0)
anchored "my_stuff1=" at 0 (checking anchored isall) minlen 10
Guessing start of match in sv for REx "my_stuff[1]=" against "my_stuff
+[1]=400"
Did not find anchored substr "my_stuff1="...
Match rejected by optimizer
Freeing REx: "my_stuff[1]="
[download]

you want /\Q$want\E/ or substr