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Re^3: quotes in Perl

by perlcapt (Pilgrim)
on Oct 21, 2004 at 00:00 UTC ( #401022=note: print w/ replies, xml ) Need Help??


in reply to Re^2: quotes in Perl
in thread quotes in Perl


Here Documents

If you want to quote many lines of text literally, you use the "Here Document" notation which consists of an introductory line which has two open angles followed by a keyword, the end tag, for signalling the end of the quote. All text and lines following the introductory line are quoted. The quote ends when the end tag is found, by itself, on a line. For example, the end tag is "EOT":
<font size="-1">#!/usr/bin/perl -w use strict; my $foo = 123.45; my $bar = "Martha Stewedprune"; print <<"EOT"; ===== This is an example of text taken literally except that variables are expanded where their variable names appear. foo: $foo bar: $bar EOT
This example, when run, produces the following:
===== This is an example of text taken literally except that variables are expanded where their variable names appear. foo: 123.45 bar: Martha Stewedprune

They way you quote, the end tag is important: like their regular quote counterparts, double-quotes allow expansion of variables and special characters, single quotes don't allow expansion. You may also have a bare, unquoted, end tag; this is equivalent to a double quote, i.e., expansion expansion.

Some warnings:

  • The end tag specifier must follow the << without any intermediate space.
  • The actual end tag must be exactly the same as in the introduction line.
  • Don't forget that the introduction line must end with a semicolon, just like any other perl statement.
The here document is particularly useful when embedding HTML in Perl because it increases the readability of the HTML. The quote character is printed out without any escapes. For example:
my $url = "http://www.maperl.com"; my $text = "Mother of Perl"; print <<"EOT"; <a href="$url">$text</a> EOT
Prints just what we would hope:
<a href="http://www.maperl.com">Mother of Perl</a>


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Re^4: quotes in Perl
by jZed (Prior) on Oct 21, 2004 at 02:35 UTC
    The other thing you need to mention is that HERE-DOCS won't interpolate if single quotes are used so print <<'EOT' won't interpolate variables in the HERE-DOC, but print <<"EOT" will.
      I believe I mentioned that where I included perlcapt's suggested material in the above tutorial. He did actually allude to that fact, but I felt it needed to be slightly more obvious, and made it so in my version. His approach to the subject was well-written, though like any rough draft it needed minor editing.

      - apotheon
      CopyWrite Chad Perrin

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