/usr/lib/guilt/guilt-header is in guilt 0.36-0.2ubuntu2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 | #!/bin/sh
#
# Copyright (c) Josef "Jeff" Sipek, 2006-2013
#
USAGE="[-eE] [<patchname>]"
if [ -z "$GUILT_VERSION" ]; then
	echo "Invoking `basename "$0"` directly is no longer supported." >&2
	exit 1
fi
_main() {
case $# in
	0)
		patch=`get_top`
		;;
	1)
		if [ "$1" = "-e" ]; then
			edit=t
			patch=`get_top`
		elif [ "$1" = "-E" ]; then
		    	edit=t
		    	full=t
			patch=`get_top`
		else
			patch="$1"
		fi
		;;
	2)
		if [ "$1" = "-e" ]; then
		    edit=t
		    patch="$2"
		elif [ "$1" = "-E" ]; then
		    edit=t
		    full=t
		    patch="$2"
 		else
		    usage
		fi
		;;
esac
# are there any patches applied?
[ -z "$patch" ] && die "No patches applied."
# check that patch exists in the series
TMP_FULL_SERIES=`get_tmp_file series`
get_full_series > "$TMP_FULL_SERIES"
found_patch=
while read x; do
	if [ "$x" = "$patch" ]; then
		found_patch="$patch"
		break
	fi
done < "$TMP_FULL_SERIES"
if [ -z "$found_patch" ]; then
	TMP_MATCHES=`get_tmp_file series`
	grep "$patch" < "$TMP_FULL_SERIES" > "$TMP_MATCHES"
	nr=`wc -l < $TMP_MATCHES`
	if [ $nr -gt 1 ]; then
		echo "$patch does not uniquely identify a patch. Did you mean any of these?" >&2
		sed 's/^/  /' "$TMP_MATCHES" >&2
		rm -f "$TMP_MATCHES" "$TMP_FULL_SERIES"
		exit 1
	elif [ $nr -eq 0 ]; then
		rm -f "$TMP_MATCHES" "$TMP_FULL_SERIES"
		die "Patch $patch is not in the series"
	fi
	found_patch=`cat $TMP_MATCHES`
	rm -f "$TMP_MATCHES"
fi
rm -f "$TMP_FULL_SERIES"
patch="$found_patch"
# FIXME: warn if we're editing an applied patch
TMP_MSG=`get_tmp_file msg`
TMP_DIFF=`get_tmp_file diff`
if [ -z "$edit" ]; then
	do_get_header "$GUILT_DIR/$branch/$patch"
else
    	if [ -n "$full" ]; then
	    git_editor "$GUILT_DIR/$branch/$patch"
	    exit $?
	fi
	do_get_full_header "$GUILT_DIR/$branch/$patch" > "$TMP_MSG"
	do_get_patch "$GUILT_DIR/$branch/$patch" > "$TMP_DIFF"
	git_editor "$TMP_MSG"
	mv "$GUILT_DIR/$branch/$patch" "$GUILT_DIR/$branch/$patch~"
	(
		cat "$TMP_MSG"
		cat "$TMP_DIFF"
	) > "$GUILT_DIR/$branch/$patch"
fi
rm -f "$TMP_MSG" "$TMP_DIFF"
}
 |