Pattern match does not work in bash script

Globbing doesn't work that way unless you enable extglob shell opt. Instead, I recommend using find:

find . -maxdepth 1 -not -name '<NAME>' -or -name '<NAME>' -delete

before running this command with -delete ensure the output is correct

Method with default settings and no external procs:

for f in *; do [[ $f =~ ^file[12]$ ]] || echo "$f"; done

The extended glob syntax you are trying to use is turned off by default; you have to enable it separately in each script where you want to use it.

shopt -s extglob

Scripts should not use ls though I imagine you were using it merely as a placeholder here.