Err...
Your data file has tags matching e.g. ']a['.

]a[1
]b[FORTUNE BAY]1[R74]c[(9)]d[58
]e[b g 9 Little Brown Jug-Gemfly (by Golden Elder (GB))]f[(BLINKERS)
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Your own code matches e.g. '[a]'.

my $a = '\[a\]';
my $b = '\[b\]';
[download]

hth,
Diz