How can I make hash key lookup case-insensitive?

问题:

Evidently hash keys are compared in a case-sensitive manner.

$ perl -e '%hash = ( FOO => 1 ); printf "%s\n", ( exists $hash{foo} ) ? "Yes" : "No";'
No

$ perl -e '%hash = ( FOO => 1 ); printf "%s\n", ( exists $hash{FOO} ) ? "Yes" : "No";'
Yes

Is there a setting to change that for the current script?

回答1:

You will have to use a tied hash. For example Hash::Case::Preserve.

回答2:

The hash of a string and the same string with the case changed are not equal. So you can't do what you want, short of calling "uc" on every hash key before you create it AND before you use it.

回答3:

my %hash = (FOO => 1);
my $key = 'fOo'; # or 'foo' for that matter

my %lookup = map {(lc $_, $hash{$_})} keys %hash;
printf "%s\n", ( exists $hash{(lc $key)} ) ? "Yes" : "No";

回答4:

grep should do the trick if you make the pattern match case insensitive:

perl -e '%hash = ( FOO => 1 ); printf "%s\n", ( scalar(grep (/^foo$/i, keys %hash)) > 0) ? "Yes" : "No";'

If you have more then one key with various spelling you may need to check if the match is greater than 1 as well.