This is a dirt-basic XML indenter. I wrote it so I could take a directory full of XML files and add newlines after tags and leading whitespace. I made no attempt to do anything comprehensive with this since it handles the simple case I was looking at.

The simple (and white-space free) document

<message><org><cn>Some org-or-other</cn><ph>Wouldn't you like to know</ph></org><contact><fn>Pat</fn><ln>Califia</ln></contact></message>

Becomes something nicer to look at

<message>
  <org>
    <cn>Some org-or-other</cn>
    <ph>Wouldn't you like to know</ph>
    </org>
  <contact>
    <fn>Pat</fn>
    <ln>Califia</ln>
    </contact>
</message>

[download]
@files = glob "*.xml";

undef $/;
for $file (@files) {
    $indent = 0;
    open FILE, $file or die "Couldn't open $file for reading: $!";
    $_ = readline *FILE;
    close FILE or die "Couldn't close $file: $!";

    # Remove whitespace between > and < if that is the only thing sepa
+rating
    # them
    s/(?<=>)\s+(?=<)//g;

    # Indent
    s{  # Capture a tag <$1$2$3>,
        # a potential closing slash $1
        # the contents $2
        # a potential closing slash $3
        <(/?)([^/>]+)(/?)> 

        # Optional white space
        \s*

        # Optional tag.
        # $4 contains either undef, "<" or "</"
        (?=(</?))?
    }
    {
        # Adjust the indentation level.
        # $3: A <foo/> tag. No alteration to indentation.
        # $1: A closing </foo> tag. Drop one indentation level
        # else: An opening <foo> tag. Increase one indentation level
        $indent +=
            $3 ?  0 :
            $1 ? -1 :
                  1;

        # Put the captured tag back into place
        "<$1$2$3>" .
        # Two closing tags in a row. Add a newline and indent the next
+ line
        ($1 and ($4 eq "</") ?
            "\n" . ("  " x $indent) : 
        # This isn't a closing tag but the next tag is. Add a newline 
+and
        # indent the next line.
        $4 ?
            "\n" . ("  " x $indent) :
        # This isn't a closing tag - no special indentation. I forget 
+why
        # this works.
            ""
        )
    # /g repeat as necessary
    # /e Execute the block of perl code to create replacement text
    # /x Allow whitespace and comments in the regex
    }gex;

    open FILE, ">", $file or die "Couldn't open $file for writing: $!"
+;
    print FILE or die "Couldn't write to $file: $!";
    close FILE or die "Couldn't close $file: $!";
}
__END__

This is the version I copied and pasted from the working script.
Its ugly so I purtied it up and posted the version you see
above this text. I'm leaving this ugly version here just in case I
introduced some bug I'm not aware of.

@files = glob "*.xml";

undef $/;
$tag = "<>/";
for $file (@files) {
    $indent = 0;
    open FILE, $file;
    $_ = <FILE>;
    s/(?<=>)\s+(?=<)//g;
    s(<(/?)([^/>]+)(/?)>\s*(?=(</?))?)($indent+=$3?0:$1?-1:1;"<$1$2$3>
+".($1&&($4 eq"</")?"\n".("  "x$indent):$4?"\n".("  "x$indent):""))ge;
    open FILE, ">$file";
    print FILE;
}

[download]

Replies are listed 'Best First'.
•Re: Light batch XML indenter
by merlyn (Sage) on May 29, 2003 at 16:25 UTC
[reply]
Re: Light batch XML indenter
by vek (Prior) on May 28, 2003 at 14:15 UTC
    diotalevi++

    You've saved me from working on something similar today - thanks. We received a bunch of XML that has no indentation or whitespace that I'll need to 'clean up'. I'll be taking your code out for a spin when I get to work today.

    Thanks again!

    -- vek --
[reply]

      This is as good a time as any to mention this but this is only something you want to do if whitespace nodes between tags isn't important to you. In my case I don't care about the introduced whitespace as data and it made some debugging easier. This isn't always a valid approach so keep that in mind.

[reply]
Re: Light batch XML indenter
by mirod (Canon) on Jun 02, 2003 at 19:44 UTC
[reply]
Re: Light batch XML indenter ( rewritten with Regexp::NamedCaptures )
by diotalevi (Canon) on Sep 19, 2005 at 17:21 UTC

    Just to see if this made things more readable, I substituted all the positional captures with named captures. See Regexp::NamedCaptures, at last for the module code.

    use Regexp::NamedCaptures;

@files = glob "*.xml";

undef $/;
for $file (@files) {
    $indent = 0;
    open FILE, $file or die "Couldn't open $file for reading: $!";
    $_ = readline *FILE;
    close FILE or die "Couldn't close $file: $!";

    # Remove whitespace between > and < if that is the only thing sepa
+rating
    # them
    s/(?<=>)\s+(?=<)//g;

    # Indent
    s{  # Capture a tag <$close_tag$name$empty_tag>,
        # a potential closing slash $close_tag
        # the contents $name
        # a potential closing slash $empty_tag
        <(?<\$close_tag>/?)(?<\$name>[^/>]+)(?<\$empty_tag>/?)>

        # Optional white space
        \s*

        # Optional tag.
        # $4 contains either undef, "<" or "</"
        (?=(?<\$next_tag_start></?))?
    }
    {
        # Adjust the indentation level.
        # $3: A <foo/> tag. No alteration to indentation.
        # $1: A closing </foo> tag. Drop one indentation level
        # else: An opening <foo> tag. Increase one indentation level
        $indent +=
            $empty_tag ?  0 :
            $close_tag ? -1 :
                       1;

        # Put the captured tag back into place
        "<$close_tag$name$empty_tag>" .
        # Two closing tags in a row. Add a newline and indent the next
+ line
        ($close_tag and ($next_tag_start eq "</") ?
            "\n" . ("  " x $indent) :
        # This isn't a closing tag but the next tag is. Add a newline 
+and
        # indent the next line.
        $next_tag_start ?
            "\n" . ("  " x $indent) :
        # This isn't a closing tag - no special indentation. I forget 
+why
        # this works.
            ""
        )
    # /g repeat as necessary
    # /e Execute the block of perl code to create replacement text
    # /x Allow whitespace and comments in the regex
    }gex;

    open FILE, ">", $file or die "Couldn't open $file for writing: $!"
+;
    print FILE or die "Couldn't write to $file: $!";
    close FILE or die "Couldn't close $file: $!";
}

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