wt-sum

#!/bin/sh
# Copyright (C) 2018 Francois Gouget
#
# A portable script to compute cryptographic checksums.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
name0=`basename "$0"`

error()
{
    echo "$name0:error:" "$@" >&2
}


### Main

opt_type=""
opt_file=""
usage=""
while [ $# -gt 0 ]
do
    arg="$1"
    shift
    case "$arg" in
    --sha1|--sha256)
        if [ -n "$opt_type" ]
        then
            error "the checksum type can only be specified once"
            opt_usage=2
            break
        fi
        opt_type="$arg"
        ;;
    --help|-h|-\?)
        usage="0"
        ;;
    *)
        if [ -n "$opt_file" ]
        then
            error "only one filename can be specified"
            opt_usage=2
            break
        fi
        opt_file="$arg"
    esac
done

if [ -z "$usage" ]
then
    if [ -z "$opt_type" ]
    then
        error "you must specify the type of checksum to compute"
        usage="2"
    fi
    if [ -z "$opt_file" ]
    then
        error "you must specify the file to checksum"
        usage="2"
    fi
fi


if [ "$usage" = "0" ]
then
    echo "Usage: $name0 [--help] (--sha1|--sha256) FILENAME"
    echo

    echo "Prints the cryptographic checksum of the specified file on stdout."
    echo

    echo "Where:"
    echo "  --sha1         Computes the SHA1 cryptographic checksum."
    echo "  --sha256       Computes the SHA256 cryptographic checksum."
    echo "  FILENAME       Is the file to checksum."
    echo "  --help, -h     Shows this help message."
    exit 0
elif [ -n "$usage" ]
then
    error "try '$name0 --help' for more information"
    exit $usage
fi


sha1_wrapper()
{
    if which sha1sum >/dev/null 2>&1
    then
        sha1sum "$@" | cut -d' ' -f1
    elif which shasum >/dev/null 2>&1
    then
       shasum -a 1 "$@" | cut -d' ' -f1
    elif which sha1 >/dev/null 2>&1
    then
       sha1 "$@" | sed -e 's/^.* = //'
    fi
}

sha256_wrapper()
{
    if which sha256sum >/dev/null 2>&1
    then
        sha256sum "$@" | cut -d' ' -f1
    elif which shasum >/dev/null 2>&1
    then
       shasum -a 256 "$@" | cut -d' ' -f1
    elif which sha256 >/dev/null 2>&1
    then
       sha256 "$@" | sed -e 's/^.* = //'
    fi
}

case "$opt_type" in
    --sha1)   sha1_wrapper "$opt_file" ;;
    --sha256) sha256_wrapper "$opt_file" ;;
esac

exit $?