Mini Shell

#!/bin/sh
#
# Copyright (c) 2003 Thomas Klausner.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

grep=${GREP:-grep}
zcat=${ZCAT:-zstdcat}

endofopts=0
pattern_found=0
grep_args=""
hyphen=0
silent=0

prog=${0##*/}

# handle being called 'zegrep' or 'zfgrep'
case $prog in
    *egrep*) prog=zegrep; grep_args='-E';;
    *fgrep*) prog=zfgrep; grep_args='-F';;
    *)       prog=zstdgrep;;
esac

# skip all options and pass them on to grep taking care of options
# with arguments, and if -e was supplied

while [ "$#" -gt 0 ] && [ "${endofopts}" -eq 0 ]; do
    case "$1" in
    # from GNU grep-2.5.1 -- keep in sync!
        -[ABCDXdefm])
            if [ "$#" -lt 2 ]; then
                printf '%s: missing argument for %s flag\n' "${prog}" "$1" >&2
                exit 1
            fi
            case "$1" in
                -e)
                    pattern="$2"
                    pattern_found=1
                    shift 2
                    break
                    ;;
                -f)
                    pattern_found=2
                    ;;
                *)
                    ;;
            esac
            grep_args="${grep_args} $1 $2"
            shift 2
            ;;
        --)
            shift
            endofopts=1
            ;;
        -)
            hyphen=1
            shift
            ;;
        -h)
            silent=1
            shift
            ;;
        -*)
            grep_args="${grep_args} $1"
            shift
            ;;
        *)
            # pattern to grep for
            endofopts=1
            ;;
    esac
done

# if no -e option was found, take next argument as grep-pattern
if [ "${pattern_found}" -lt 1 ]; then
    if [ "$#" -ge 1 ]; then
        pattern="$1"
        shift
    elif [ "${hyphen}" -gt 0 ]; then
        pattern="-"
    else
        printf '%s: missing pattern\n' "${prog}" >&2
        exit 1
    fi
fi

EXIT_CODE=0
# call grep ...
if [ "$#" -lt 1 ]; then
    # ... on stdin
    set -f # Disable file name generation (globbing).
    # shellcheck disable=SC2086
    "${zcat}" -fq - | "${grep}" ${grep_args} -- "${pattern}" -
    EXIT_CODE=$?
    set +f
else
    # ... on all files given on the command line
    if [ "${silent}" -lt 1 ] && [ "$#" -gt 1 ]; then
        grep_args="-H ${grep_args}"
    fi
    set -f
    while [ "$#" -gt 0 ]; do
        # shellcheck disable=SC2086
        if [ $pattern_found -eq 2 ]; then
            "${zcat}" -fq -- "$1" | "${grep}" --label="${1}" ${grep_args} -- -
        else
            "${zcat}" -fq -- "$1" | "${grep}" --label="${1}" ${grep_args} -- "${pattern}" -
        fi
        [ "$?" -ne 0 ] && EXIT_CODE=1
        shift
    done
    set +f
fi

exit "${EXIT_CODE}"