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for ( 'A_TAG_HSSL_LBA_1', 'A_TAG_HSSL_LBAB_1' ) {
    if( ! /A_[A_Z0-9_]+/i) {
...
        print "$_ matches\n";
    }
}

A_TAG_HSSL_LBA_1 matches
A_TAG_HSSL_LBAB_1 is not matching

/^           # start of string
  A_         # must start "A_"
...
 $           # end of string
/ix          # allow spaces and comments inside regexp
             # and ignore case