I have an idiom I use a lot to do quick searches through log files or data streams, or to do a "uniq" on a file without having to sort it.

Using a hash to keep track of what has already gone by is quite common. Even the name you used is seen everywhere: %seen. You can however make it a bit faster. You're now increasing $seen{$1} every time, while you don't really care if it's 1 or 2 or 3, as long as it's not 0 (undef). 

perl -ne'$seen{$_}++, print unless $seen{$_}';

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It's not great for your golf score, but it can be a lot faster!

Speaking of golf, you could try this one to improve your golf score: 
#        123456789_12345
perl -pe'$_=""if$s{$_}++'

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Or, using evil symbolic references: 
#        123456789_12
perl -pe'$_=""if$$_++'

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(Can break when the last line has no trailing linefeed, and equals the name of a special (scalar) variable ;)) 

U28geW91IGNhbiBhbGwgcm90MTMgY
W5kIHBhY2soKS4gQnV0IGRvIHlvdS
ByZWNvZ25pc2UgQmFzZTY0IHdoZW4
geW91IHNlZSBpdD8gIC0tIEp1ZXJk

In reply to Re: Better "uniq" idiom? by Juerd
in thread Better "uniq" idiom? by RMGir

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