Question

I’m a newbie to Perl and I found this test CGI script in my Apache installation and I would like to know what it does, especially in one of the two s/// lines.

#!/usr/bin/perl

print "Content-type: text/plain; charset=iso-8859-1\n\n";
foreach $var (sort(keys(%ENV))) {
    $val = $ENV{$var};
    $val =~ s|\n|\\n|g;
    $val =~ s|"|\\"|g;
    print "${var}=\"${val}\"\n";
}

The $val =~ s|\n|\\n|g; line replaces every occurrence of \n with \\n. But why?

And what about the $val =~ s|"|\\"|g; line? I think it’s a substitution, but it seems to have a weird form.

Answer 1

The $val =~ s|\n|\\n|g; line replaces every occurrence of \n with \\n.

More precisely, it replaces each new line with a common escape sequence that represents a new line.

But why?

There lies the land of pure speculation. The content-type is text/plain so there is no obvious reason to do it.

$val =~ s|"|\\"|g; line? I think it’s a substitution, but it seems to have a weird form.

It replaces " with an escape sequence representing a " in many contexts (but not plain text). Again, there is no obvious reason to do it from the context it is presented in.

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To hazard a guess. It looks like it is designed to dump the server’s environment to a text file from which it can be copy/pasted to be used elsewhere.