detab Perl Code List

This is the Perl code for detab, a small program for converting tabs to spaces two different ways. I usually had to run this a few times with different options to see what worked best for a file.

---

#!/usr/bin/perl

# This program borrows heavily from Usenet postings on
# comp.lang.perl.misc and one or more O'Reilly Perl books (Programming
# Perl and/or Perl Cookbook) for the column mode of tab replacement.

# --Kent Nassen, 5/5/1999 (v1.0)

use strict;
use Getopt::Std;

our ($version, $ProgName, $tablen, $mode, $opt_h, $opt_l, $opt_m);

#$version="(v1.0, 5/5/1999)";
$version="(v1.1, 9/22/2025)";
($ProgName = $0) =~ s%.*/%%;

getopts('hl:m:');

# Default tab width is 8
if (!$opt_l) { $tablen=8 }
elsif ($opt_l>0) { $tablen=$opt_l }
else { print STDERR "\n   *** Bad tab length: $opt_l\n"; &DisplayUsage }

# Default tab replace mode is "column"
if ($opt_m) { $mode=$opt_m } else { $mode="column" }

# Found -h so display usage message
if ($opt_h) { &DisplayUsage }

while (<>) {
	if ($mode eq "literal") {
	# This does literal tab-->fixed # of spaces
	# For example, if you have "Testsome stuff" and 8 chars per tab,
	# in literal mode, you'll get "Test        some stuff"
	#                                  ^^^^^^^^
	#                                  8 spaces
	  while ( $_ =~ s/\t/" " x ($tablen)/eg ) { } 
  	}
	elsif ($mode eq "column") {
	# This does tab-->actual column location starting from position of tab
	# For example, if you have "Testsome stuff" and 8 chars per tab,
	# in column mode, you'll get "Test   some stuff"
	#                                    ^
	#                             column 8
	  while ( $_ =~ s/\t/" " x ($tablen - length($`) % $tablen)/eg ) { } 
  	}
        if (/[^\t]/) { print }
	else { print STDERR "\n   *** Bad tab replacement mode: $mode\n"; &DisplayUsage }
}

sub DisplayUsage {
print STDERR "\n    $ProgName: replace tabs with spaces\n",
	"    by Kent Nassen, $version\n\n",
	"    Usage:  $ProgName [-h][-l #][-m mode] [filename]\n\n",
	"    -h       Show this usage message\n",
	"    -l\#      Each tab is worth up to \# spaces.  8 spaces per tab is the\n",
	"             default.\n",
	"    -m mode  Where mode is one of: 'column' or 'literal', indicating the\n",
	"             tab replacement mode, either spacing to the actual column\n",
	"             location indicated by the tab (may be less than -l spaces) or\n",
	"             a literal replacement of each tab by -l spaces without regard to\n",
	"             to which column.  column mode is the default.\n\n",
	"    If no filename is given, the program will read from stdin\n\n";
exit;
}

Last modified: Mon Sep 22 15:50:43 EDT 2025