What happens to characters not specified in the first part of Perl's tr/// operator?

Question

I am using Perl for string manipulation and that involves use of the reverse function and of tr to translate my string. The script reads some strings and then performs following:

$revread = reverse($newword);
$revread =~ tr/TACGN/ATGCN/;

So the word is reversed and then gets translated--reverse complement. I have following question:

What if

$revread=~ tr/TACG/ATGC/;

is used. In this case if "N" is found will it be skipped? as in tr I have nothing there to translate it to OR it will be printed as just as "N".

Why would you think that "N" would be removed? Makes no sense to me. — TLP, Nov 24 '11 at 14:14
Perhaps the OP is concerned with any unexpected behavior and that's why he's asking — Zaid, Nov 24 '11 at 14:14
Yes, wanted to make sure that I do not see something unexpected — Sudeep, Nov 24 '11 at 18:34

score 5 · Answer 1 · answered Nov 24 '11 at 14:17

5

Yes, anything that is not specified inside to tr will be left alone.

The documentation for tr/// is a little hard to get to as it's detailed examples are listed in perldoc perlop rather than the usual perldoc perlfunc

answered Nov 24 '11 at 14:17

Zaid

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Thanks. Very clear now. The perl doc cleared other doubts as well...now it will be the first go to place.. – Sudeep Nov 24 '11 at 14:25
The documentation for tr/// is in perlop, not perlfunc because it's an operator, not a function :-) – Dave Cross Nov 24 '11 at 14:56
The latest patches to perldoc will now find tr with the -f switch :) – brian d foy Nov 24 '11 at 17:08

TLP · Answer 2 · 2011-11-24T14:32:57.297

2

Aleks G has the correct answer: Just try it.

I tried it. I found that:

> perl -wE '$x = qq(abcdefg); $x=~ tr/abc/123/; say $x;'
123defg

Any characters not found in the transliteration are left as they are. Documentation here.

edited Nov 24 '11 at 14:32

answered Nov 24 '11 at 14:20

TLP

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What happens to characters not specified in the first part of Perl's tr/// operator?

2 Answers2