How to run the syntax-highlighting.sh command for cgit to check it works properly

The syntax highlighting option in a cgit installation is no working properly and I want to see if it will run properly from the command line if all the necessary parameters are present.

The option in /etc/cgitrc is correctly set.

source-filter=/usr/lib/cgit/filters/syntax-highlighting.sh

When I ran the highlight command on a bash file for instance the css and span classes are in the output, but when I run /usr/lib/cgit/filters/syntax-highlighting.sh on the file the css and span tags don't show.

The command actual highlight command in the script (the last line) is

exec highlight --force --inline-css -f -I -O xhtml -S "$EXTENSION" 2>/dev/null

#!/bin/sh
# This script can be used to implement syntax highlighting in the cgit
# tree-view by refering to this file with the source-filter or repo.source-
# filter options in cgitrc.
#
# This script requires a shell supporting the ${var##pattern} syntax.
# It is supported by at least dash and bash, however busybox environments
# might have to use an external call to sed instead.

#
# Code considered irrelevant snipped
#

# store filename and extension in local vars
BASENAME="$1"
EXTENSION="${BASENAME##*.}"

[ "${BASENAME}" = "${EXTENSION}" ] && EXTENSION=txt
[ -z "${EXTENSION}" ] && EXTENSION=txt

# map Makefile and Makefile.* to .mk
[ "${BASENAME%%.*}" = "Makefile" ] && EXTENSION=mk

# highlight versions 2 and 3 have different commandline options. Specifically,
# the -X option that is used for version 2 is replaced by the -O xhtml option
# for version 3.
#
# Version 2 can be found (for example) on EPEL 5, while version 3 can be
# found (for example) on EPEL 6.
#
# This is for version 2
#exec highlight --force -f -I -X -S "$EXTENSION" 2>/dev/null

# This is for version 3
exec highlight --force --inline-css -f -I -O xhtml -S "$EXTENSION" 2>/dev/null