#!/bin/bash

# Troels Arvin <troels@arvin.dk>, $Date: 2010-09-07 13:01:26 +0200 (Tue, 07 Sep 2010) $.
# Script to compensate for Linux' grep not having the equivalent
# of AIX' "grep -p" (paragraph grep).
# Public domain script. Use it on your own risk.
# Latest version at http://troels.arvin.dk/code/shell/pargrep/

thisscript=`basename $0`
negated=''
insensitive=''
needle=''

err () {
    msg="$1"
    echo "error while running $thisscript: $msg" >&2
    exit 1
}

usage () {
    echo "Usage:"
    echo "$thisscript [-i] [-v] <regex>"
    echo
    echo " -i: match case insentitively"
    echo " -v: negate matching"
    echo
    echo "Searches standard input for <regex>, paragraph per paragraph,"
    echo "somewhat alike AIX' 'grep -p'."
    echo "Perl is used behind the back, so regex style i perl-regex."
    exit 0
}

[ "$1" == '-h' -o "$1" == '--help' ] && usage

while getopts ":vi" options; do
    case "$options" in
        v)
            negated='not'
            ;;
        i)
            insensitive='i'
            ;;
        *)
            err "unknown argument $OPTARG"
            ;;
    esac
done
shift $(($OPTIND - 1))

needle="$1"

[ -z "$needle" ] && err "no search string indicated"

perl -ne "BEGIN {\$/ = \"\n\n\"} print if $negated /$needle/${insensitive}"