--- /dev/null
+#!/usr/bin/perl
+# Work out paths in a subversion repository for branches or tags of the
+# given directory. Works on current directory by default, or it can be given
+# a path.
+
+my $wanted=shift;
+
+# Get the svn url of the current directory.
+my $url = `svn info @ARGV| grep -i ^URL: | cut -d ' ' -f 2`;
+if (! length $url) {
+ die "cannot get url";
+}
+
+if (length $wanted) {
+ # Now jut substitute into it.
+ $url=~s!/(?:trunk|branches|tags)($|/)!/$wanted$1!;
+}
+print $url;