You want to reverse the characters or words of a string.
Use the reverse
function in scalar context for flipping bytes.
$revbytes = reverse($string);
To flip words, use reverse
in list context with split
and join
:
$revwords = join(" ", reverse split(" ", $string));
The reverse
function is two different functions in one. When called in scalar context, it joins together its arguments and returns that string in reverse order. When called in list context, it returns its arguments in the opposite order. When using reverse
for its byte-flipping behavior, use scalar
to force scalar context unless it's entirely obvious.
$gnirts = reverse($string); # reverse letters in $string @sdrow = reverse(@words); # reverse elements in @words $confused = reverse(@words); # reverse letters in join("", @words)
Here's an example of reversing words in a string. Using a single space, " ", as the pattern to split
is a special case. It causes split
to use contiguous whitespace as the separator and also discard any leading null fields, just like awk. Normally, split
discards only trailing null fields.
# reverse word order
$string = 'Yoda said, "can you see this?"';
@allwords = split(" ", $string);
$revwords = join(" ", reverse @allwords);
print $revwords, "\n";
this?" see you "can said, Yoda
We could remove the temporary array @allwords
and do it on one line:
$revwords = join(" ", reverse split(" ", $string));
Multiple whitespace in $string
becomes a single space in $revwords
. If you want to preserve whitespace, use this:
$revwords = join("", reverse split(/(\s+)/, $string));
One use of reverse
is to test whether a word is a palindrome (a word that reads the same backward or forward):
$word = "reviver"; $is_palindrome = ($word eq reverse($word));
We can turn this into a one-liner that finds big palindromes in /usr/dict/words.
% perl -nle 'print if $_ eq reverse && length > 5' /usr/dict/words
deedeed
degged
deified
denned
hallah
kakkak
murdrum
redder
repaper
retter
reviver
rotator
sooloos
tebbet
terret
tut-tut
The split
, reverse
, and scalar
functions in perlfunc (1) and Chapter 3 of Programming Perl; the "Switches" section of perlrun (1) and Chapter 6 of Programming Perl
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