A basic perl implementation of grep switches : -A , -B , -v , -P, -i

grep.pl

#!/usr/bin/perl

# NOTE1: this script works only with stdin/pipe so use it like 'cat FILE | grep.pl -P ...'
# NOTE2: -A and -B features don't mix well if matching lines are in cross section

## this is a basic implementation of grep switches : -A , -B , -v , -P, -i
#  reason: Mac doesn't support "grep -P"
#    > OS X's grep changed from grep (GNU grep) 2.5.1 in 10.7 to grep (BSD grep) 2.5.1-FreeBSD in 10.8
#       -- https://stackoverflow.com/questions/16658333/grep-p-no-longer-works-how-can-i-rewrite-my-searches

## sample oneliners that were used before making of this script
#  - equivalent to 'grep -P "PATTERN"'
#      perl -e'while(<>){if( (m!PATTERN!) ){$ok++;print}};if(!($ok)){exit 1}'
#  - equivalent to 'grep -P -i "PATTERN"'
#      perl -e'while(<>){if( (m!PATTERN!i) ){$ok++;print}};if(!($ok)){exit 1}'
#  - equivalent to 'grep -v -P "PATTERN"'
#      perl -e'while(<>){if( !(m!PATTERN!) ){$ok++;print}};if(!($ok)){exit 1}'

# basic algorithm from here: https://www.perlmonks.org/?node_id=779717

use strict;
use warnings;

my $linesA = "";
my $linesB = "";
my $inverse = "";
my $ignoreCase = "";
my $regex = "";

my $inErr = "";
my $err = "";
my $help = "";

$help .= "\nWRONG ARGUMENT INPUT!  Exiting..";
$help .= "\n\nUsage:\n$0 OPTIONS\n\nOPTIONS:\n";
$help .= "\n\t-P=REGEX";
$help .= "\n\t-v";
$help .= "\n\t-A=NUM             ; -A and -B don't mix well if matching lines are in cross section";
$help .= "\n\t-B=NUM             ; -A and -B don't mix well if matching lines are in cross section";
$help .= "\n\nEXAMPLE: \n\tcat FILE | $0 -A=5 -v -P='^ *#'   ; print following 5 lines where the grepped line is not a comment";
$help .= "\n\n";

## ARGUMENTS FETCH

for (my $iargv=0; $iargv<=$#ARGV; $iargv++) {
     my @param;
     if ($ARGV[$iargv] =~ m/^\-A\=/i) {
           @param = split(/=/, $ARGV[$iargv]);
           $linesA=$param[1];
     }
     elsif ($ARGV[$iargv] =~ m/^\-B\=/i) {
           @param = split(/=/, $ARGV[$iargv]);
           $linesB=$param[1];
     }
     elsif ($ARGV[$iargv] =~ m/^\-v$/i) {
           $inverse = 1;
     }
     elsif ($ARGV[$iargv] =~ m/^\-i$/i) {
           $ignoreCase = 1;
     }
     elsif ($ARGV[$iargv] =~ m/^\-P\=/i) {
           @param = split(/=/, $ARGV[$iargv]);
           $regex=$param[1];
     }
     else {
           print $help;
           exit;
     }
}

if (scalar(@ARGV)==0) {
     $inErr .= "\n  Error! No input arguments. \n";
}

if ($inErr ne "") {
     print $inErr . "\n" .$help;
     exit;
}

my ($prev, $next);
my @aLinesA;
my @aLinesB;
my $lineCount=0;
my $matchedLinesCount=0;

while (my $line = <STDIN>) {
    $lineCount++;
    if ( $linesA && $next ) {
        print "$line";
        # print "linesA=$linesA , next=$next \n";
        if ( $next >= $linesA ) {
            $next = undef;
        }
        else {
            $next++;
        }
    }
    if ($inverse) {
        if ($ignoreCase) {
            if ( $line !~ m/$regex/i ) {
                $matchedLinesCount++;
                if (defined( $prev )) {
                    # print @aLinesB;
                    # print "prev=$prev\n";
                    # print "--\n";
                    for (my $i=$#aLinesB-$linesB+1 ; $i<=$#aLinesB ; $i++) {
                        print "$aLinesB[$i]";
                    }
                }
                $prev = undef;
                @aLinesB=();
                print "$line";
                if (!($next)) {
                    $next++;
                }
            }
        }
        else {
            if ( $line !~ m/$regex/ ) {
                $matchedLinesCount++;
                if (defined( $prev )) {
                    # print @aLinesB;
                    # print "prev=$prev\n";
                    # print "--\n";
                    for (my $i=$#aLinesB-$linesB+1 ; $i<=$#aLinesB ; $i++) {
                        print "$aLinesB[$i]";
                    }
                }
                $prev = undef;
                @aLinesB=();
                print "$line";
                if (!($next)) {
                    $next++;
                }
            }
        }
    }
    else {
        if ($ignoreCase) {
            if ( $line =~ m/$regex/i ) {
                $matchedLinesCount++;
                if (defined( $prev )) {
                    # print @aLinesB;
                    # print "prev=$prev\n";
                    # print "--\n";
                    for (my $i=$#aLinesB-$linesB+1 ; $i<=$#aLinesB ; $i++) {
                        print "$aLinesB[$i]";
                    }
                }
                $prev = undef;
                @aLinesB=();
                print "$line";
                if (!($next)) {
                    $next++;
                }
            }
        }
        else {
            if ( $line =~ m/$regex/ ) {
                $matchedLinesCount++;
                if (defined( $prev )) {
                    # print @aLinesB;
                    # print "prev=$prev\n";
                    # print "--\n";
                    for (my $i=$#aLinesB-$linesB+1 ; $i<=$#aLinesB ; $i++) {
                        print "$aLinesB[$i]";
                    }
                }
                $prev = undef;
                @aLinesB=();
                print "$line";
                if (!($next)) {
                    $next++;
                }
            }
        }
    }
    if ( $linesB ) {
        $prev++;
        push(@aLinesB, $line);
    }
}

if (!($matchedLinesCount)) {
    exit 1;
}