Perl: Difference between revisions

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-==Running a Perl script==
+== Running a Perl script ==
-Common problems and solutions:
+=== Replacing #! with nix-shell ===
+Perl scripts normally start something like this:
+<syntaxHighlight lang=shell>
+  #!/usr/bin/env perl
+</syntaxHighlight>
+In Nix, we often make isolated environments using [https://nixos.org/manual/nix/unstable/command-ref/nix-shell.html nix-shell]. You can do this in the <code>#!</code> (shabang) section directly in the script too. Here is an example from the manual &mdash; a Perl script that specifies that it requires Perl and the HTML::TokeParser::Simple and LWP packages:
+<syntaxHighlight lang=perl>
+#! /usr/bin/env nix-shell
+#! nix-shell -i perl -p perl perlPackages.HTMLTokeParserSimple perlPackages.LWP
+use HTML::TokeParser::Simple;
+# Fetch nixos.org and print all hrefs.
+my $p = HTML::TokeParser::Simple->new(url => 'http://nixos.org/');
+while (my $token = $p->get_tag("a")) {
+    my $href = $token->get_attr("href");
+    print "$href\n" if $href;
+}
+</syntaxHighlight>
+=== Invoking nix-shell on command-line ===
 <code>Can't locate DB_File.pm in @INC (you may need to install the DB_File module)</code>: run it with <code>nix-shell -p perl -p perlPackages.DBFile --run ./myscript.pl</code>