add a small perl example wrapper script for i3status’s JSON output

contrib/wrapper.pl

@@ -0,0 +1,43 @@
+#!/usr/bin/env perl
+# vim:ts=4:sw=4:expandtab
+# © 2012 Michael Stapelberg, Public Domain
+
+# This script is a simple wrapper which prefixes each i3status line with custom
+# information. To use it, ensure your ~/.i3status.conf contains this line:
+#     output_format = "i3bar"
+# in the 'general' section.
+# Then, in your ~/.i3/config, use:
+#     status_command i3status | ~/i3status/contrib/wrapper.pl
+# In the 'bar' section.
+
+use strict;
+use warnings;
+# You can install the JSON module with 'cpan JSON' or by using your
+# distribution’s package management system, for example apt-get install
+# libjson-perl on Debian/Ubuntu.
+use JSON;
+
+# Don’t buffer any output.
+$| = 1;
+
+# Skip the first line which contains the version header.
+print scalar <STDIN>;
+
+# The second line contains the start of the infinite array.
+print scalar <STDIN>;
+
+# Read lines forever, ignore a comma at the beginning if it exists.
+while (my ($statusline) = (<STDIN> =~ /^,?(.*)/)) {
+    # Decode the JSON-encoded line.
+    my @blocks = @{decode_json($statusline)};
+
+    # Prefix our own information (you could also suffix or insert in the
+    # middle).
+    @blocks = ({
+        full_text => 'MPD: not running',
+        name => 'mpd'
+    }, @blocks);
+
+    # Output the line as JSON.
+    print encode_json(\@blocks) . ",\n";
+}