FAQ 4.49: How do I process/modify each element of an array?

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

This message is one of several periodic postings to comp.lang.perl.misc
intended to make it easier for perl programmers to find answers to
common questions. The core of this message represents an excerpt
from the documentation provided with Perl.


4.49: How do I process/modify each element of an array?

    Use "for"/"foreach":

        for (@lines) {
            s/foo/bar/;     # change that word
            y/XZ/ZX/;       # swap those letters

    Here's another; let's compute spherical volumes:

        for (@volumes = @radii) {   # @volumes has changed parts
            $_ **= 3;
            $_ *= (4/3) * 3.14159;  # this will be constant folded

    which can also be done with map() which is made to transform one list
    into another:

            @volumes = map {$_ ** 3 * (4/3) * 3.14159} @radii;

    If you want to do the same thing to modify the values of the hash, you
    can use the "values" function. As of Perl 5.6 the values are not copied,
    so if you modify $orbit (in this case), you modify the value.

        for $orbit ( values %orbits ) {
            ($orbit **= 3) *= (4/3) * 3.14159;

    Prior to perl 5.6 "values" returned copies of the values, so older perl
    code often contains constructions such as @orbits{keys %orbits} instead
    of "values %orbits" where the hash is to be modified.


Documents such as this have been called "Answers to Frequently
Asked Questions" or FAQ for short.  They represent an important
part of the Usenet tradition.  They serve to reduce the volume of
redundant traffic on a news group by providing quality answers to
questions that keep coming up.

If you are some how irritated by seeing these postings you are free
to ignore them or add the sender to your killfile.  If you find
errors or other problems with these postings please send corrections
or comments to the posting email address or to the maintainers as
directed in the perlfaq manual page.

Note that the FAQ text posted by this server may have been modified
from that distributed in the stable Perl release.  It may have been
edited to reflect the additions, changes and corrections provided
by respondents, reviewers, and critics to previous postings of
these FAQ. Complete text of these FAQ are available on request.

The perlfaq manual page contains the following copyright notice.


    Copyright (c) 1997-2002 Tom Christiansen and Nathan
    Torkington, and other contributors as noted. All rights

This posting is provided in the hope that it will be useful but
does not represent a commitment or contract of any kind on the part
of the contributers, authors or their agents.

Site Timeline