git pre-commit hook to check XML files for well-formedness, using 'file' and 'xmllint' commands

pre-commit

#!/bin/sh
#
# An example hook script to verify what is about to be committed.
# Called by "git commit" with no arguments.  The hook should
# exit with non-zero status after issuing an appropriate message if
# it wants to stop the commit.
#
# To enable this hook, rename this file to "pre-commit".

if git rev-parse --verify HEAD >/dev/null 2>&1
then
        against=HEAD
else
        # Initial commit: diff against an empty tree object
        against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

# If you want to allow non-ascii filenames set this variable to true.
allownonascii=$(git config hooks.allownonascii)

# Redirect output to stderr.
exec 1>&2

# Cross platform projects tend to avoid non-ascii filenames; prevent
# them from being added to the repository. We exploit the fact that the
# printable range starts at the space character and ends with tilde.
if [ "$allownonascii" != "true" ] &&
        # Note that the use of brackets around a tr range is ok here, (it's
        # even required, for portability to Solaris 10's /usr/bin/tr), since
        # the square bracket bytes happen to fall in the designated range.
        test $(git diff --cached --name-only --diff-filter=A -z $against |
          LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
then
        echo "Error: Attempt to add a non-ascii file name."
        echo
        echo "This can cause problems if you want to work"
        echo "with people on other platforms."
        echo
        echo "To be portable it is advisable to rename the file ..."
        echo
        echo "If you know what you are doing you can disable this"
        echo "check using:"
        echo
        echo "  git config hooks.allownonascii true"
        echo
        exit 1
fi

check_xml_wellformed()
{
        for FILE in `git diff --cached --name-only` ; do
                file_extension=${FILE##*.}
                # if file is an xml file, check that it is well-formed
                if [ $file_extension == 'xml' ]; then
                        if ! xmllint --noout $FILE; then
                                echo "========================================================="
                                echo "Unstaging $FILE for the commit -- XML but not well-formed"
                                git reset -q HEAD $FILE
                                retval=1
                        else
                                echo "XML check for $FILE: OK"
                        fi
                fi
        done

    if [[ $retval -gt 0 ]]; then
        exit $retval
    fi
}

check_xml_wellformed

# If there are whitespace errors, print the offending file names and fail.
exec git diff-index --check --cached $against --

Check the file extension rather than mime-type