Perl Cookbook

Program: words

Description

Have you ever wondered how programs like ls generate columns of sorted output that you read down the columns instead of across the rows? For example:

awk      cp       ed       login    mount    rmdir    sum
basename csh      egrep    ls       mt       sed      sync
cat      date     fgrep    mail     mv       sh       tar
chgrp    dd       grep     mkdir    ps       sort     touch
chmod    df       kill     mknod    pwd      stty     vi
chown    echo     ln       more     rm       su

Example 4.2 does this.

Example 4-2. words

#!/usr/bin/perl -w # words - gather lines, present in columns use strict; my ($item, $cols, $rows, $maxlen); my ($xpixel, $ypixel, $mask, @data); getwinsize(); # first gather up every line of input, # remembering the longest line length seen $maxlen = 1; while (<>) { my $mylen; s/\s+$//; $maxlen = $mylen if (($mylen = length) > $maxlen); push(@data, $_); } $maxlen += 1; # to make extra space # determine boundaries of screen $cols = int($cols / $maxlen) || 1; $rows = int(($#data+$cols) / $cols); # pre-create mask for faster computation $mask = sprintf("%%-%ds ", $maxlen-1); # subroutine to check whether at last item on line sub EOL { ($item+1) % $cols == 0 } # now process each item, picking out proper piece for this position for ($item = 0; $item < $rows * $cols; $item++) { my $target = ($item % $cols) * $rows + int($item/$cols); my $piece = sprintf($mask, $target < @data ? $data[$target] : ""); $piece =~ s/\s+$// if EOL(); # don't blank-pad to EOL print $piece; print "\n" if EOL(); } # finish up if needed print "\n" if EOL(); # not portable -- linux only sub getwinsize { my $winsize ...