#!/usr/bin/perl
use Getopt::Long;

sub usage {
    my $msg= "Usage: $0 <perl code> <filelist>\n"
	. "This modifies all the files on the list line-by-line\n"
	. "using the included perl code.  The code is run line by line,\n"
	. "as if it were in a 'while (<>)' loop or -w mode.  For example,\n"
	. "the code 's/oldstring/newstring/' would replace oldstring\n"
	. "with newstring throughout all the files. \n"
	. "Options: \n"
	. "  -h        Print this message. \n"
	. "  -saveold  Saves the old version of the file as '<file>.old'\n"
	. "  -s        Treat the entire file as a single line which the\n"
	. "            the code then acts on.\n"
	. "Options: \n";
    return $msg;
}
my ($help, $saveold, $single);
GetOptions("h" => \$help, "help" => \$help, "saveold" => \$saveold,
	   "s" => \$single);
if ($help) { print usage(); exit; }


my $code = shift;
my @filelist= ();
foreach (@ARGV) { push @filelist, glob($_); }

foreach (@filelist) {
    my $thisfile= $_;
    my $mode = (stat($thisfile))[2];
    my $tempfile= $_ . '.temp';
    open(THISFILE, "$thisfile");
    open(TEMPFILE, ">$tempfile");
    if ($single) {
	my $string;
	while (<THISFILE>) { $string.=$_; }
	$_= $string;
	eval($code);
	print TEMPFILE $_;
    } else {
	while (<THISFILE>) {
	    eval($code);
	    print TEMPFILE $_;
	}
    }
    close(THISFILE);
    close(TEMPFILE);
    if ($saveold) {
	rename($thisfile,"$thisfile.old");
    } else {
	unlink($thisfile);
    }
    rename($tempfile, $thisfile);
    chmod($mode,$thisfile);
} # end of foreach @filelist