FAQ 4.22 How do I expand function calls in a string?


PerlFAQ Server

This is an excerpt from the latest version perlfaq4.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .


4.22: How do I expand function calls in a string?

(contributed by brian d foy)

This is documented in perlref, and although it's not the easiest thing
to read, it does work. In each of these examples, we call the function
inside the braces used to dereference a reference. If we have more than
one return value, we can construct and dereference an anonymous array.
In this case, we call the function in list context.

print "The time values are @{ [localtime] }.\n";

If we want to call the function in scalar context, we have to do a bit
more work. We can really have any code we like inside the braces, so we
simply have to end with the scalar reference, although how you do that
is up to you, and you can use code inside the braces. Note that the use
of parens creates a list context, so we need "scalar" to force the
scalar context on the function:

print "The time is ${\(scalar localtime)}.\n"

print "The time is ${ my $x = localtime; \$x }.\n";

If your function already returns a reference, you don't need to create
the reference yourself.

sub timestamp { my $t = localtime; \$t }

print "The time is ${ timestamp() }.\n";

The "Interpolation" module can also do a lot of magic for you. You can
specify a variable name, in this case "E", to set up a tied hash that
does the interpolation for you. It has several other methods to do this
as well.

use Interpolation E => 'eval';
print "The time values are $E{localtime()}.\n";

In most cases, it is probably easier to simply use string concatenation,
which also forces scalar context.

print "The time is " . localtime() . ".\n";


The perlfaq-workers, a group of volunteers, maintain the perlfaq. They
are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in


Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question