hi,

time ago a monk asked how to s/// using an hash for key/value substitution.

knowing the keys of the hash, it would be easy to: 

s/(key1|key2|key3)/$hash{$1)/g;

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in a more generic way, the RE can be built using qr: 
my $re = join '|', keys %dict;
$re = qr|($re)|;
s/$re/$hash{$1}/g;

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with a CPAN module, you can: 
use Regexp::Assemble;
my $ra = Regexp::Assemble->new;
$ra->add($_) for keys %dict;

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which returns a more clever pattern. Or: 
s/(\w+)/$dict{$1}||$1/ge;

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(Note some differences between those approaches. The last one will "update" the string also when it shouldn't, by replacing with the same text. this can be a problem if i want to match 'bcd' in 'abcde' -- in this case s/// will change abcde with abcde and pass over, it does not check bcd!)

I looked on perlre to findout if we can do assertions on a RE, (?{code}) is an "always true" statement1, a pity we can't use to stop the parsing. but after some digging i found that (?(?{cond})|(?!)) fails if cond isn't true, so: 

s/(\w+)(?(?{$dict{$1}})|(?!))/$dict{$1}/g;

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This way avoid to prepare the RE before, but match bcd against abcde.

This seems to be a misleading (yet usefull) feature. it means that (${code}) isn't an "always true" assertion. But is it reliable enough to be used?

1 -- seems this will be changed in perl 6.

Update: corrected a missing ) in the last RE.

In reply to regex s/// using hash by oha

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