Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl Monk, Perl Meditation

How do I empty out a hash?

by vroom (Pope)
on Mar 02, 2000 at 23:36 UTC ( #4687=categorized question: print w/replies, xml ) Need Help??
Contributed by vroom on Mar 02, 2000 at 23:36 UTC
Q&A  > hashes

Answer: How do I empty out a hash?
contributed by vroom

You can set it equal to an empty hash or undef it;

%hash=(); undef %hash;
Answer: How do I empty out a hash?
contributed by arno


To delete a key, you don't need to know her value.
Here's my code :

my %hash = ( Carol => 22, Mary => 21, Chris => 30 ); map { delete $hash{$_} } keys %hash;
Update: Of course this makes use of map in void context. Yick. And a couple other suggestions came in by way of followup:

  • delete @hash{(keys %hash)}; # Hash slice
  • %hash = (); # Most efficient method.


Answer: How do I empty out a hash?
contributed by DigitalKitty


You could also iterate over the hash and delete each key/value pair with this:

#!/usr/bin/perl -w use strict; my %hash = ( Carol => 22, Mary => 21, Chris => 30 ); my( $k, $v); while(( $k, $v) = each %hash ) { delete $hash{$k}; }

The previous solutions are more efficient but I thought you might appreciate an alternate method.

Update: Several followups included these suggestions:

  • for (keys %hash) { delete $hash{$_};};
  • delete $hash{$_} for keys %hash;

Both of those methods ignore the values, which are unimportant when deleting hash table entries.

Hope this helps,

Please (register and) log in if you wish to add an answer

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others having an uproarious good time at the Monastery: (5)
    As of 2020-10-30 01:10 GMT
    Find Nodes?
      Voting Booth?
      My favourite web site is:

      Results (276 votes). Check out past polls.