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Reimplementation of cut in Perl

News Unix cut command Recommended Links Perl power tools Recommended Papers Rcut Reference Pipes
 IFS tr AWK bash Tips and Tricks   Tips Humor Etc

ppt project now was moved to SPAN.

See Casey West - ppt-0.14 - search.cpan.org

Source tree at Sourceforge is still exists: SourceForge.net Repository - [ppt] Index of -ppt-bin

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Old News ;-)

PERL Beginners - Perl equivalent to the unix 'cut' command

On Thu, 14 Oct 2004, Chris Devers wrote:
> On Thu, 14 Oct 2004, Dave Kettmann wrote:
>
>
> Okay then.
>
> perldoc -f split
>
> Also speaks for itself :-)

To be less snarky, you probably need to open up your file, iterate over it line by line, using split to break each line up into chunks, then write out a new array with the fields you want and the order you want them. This second array can then be written out to disc; if you want you could even read & write within the same loop.

But the key point is that split is often the easiest way to break apart the fields in a file that is, for example, CSV formatted.

Give that a try, write some code to attempt it, and let the list know if you have any problems in getting it to work.


--
Chris Devers

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Here is a source code of reimplementation used in Perl Power tools taken from Sourceforge repository:

#!/usr/bin/env perl
#   
# cut -- remove sections from each line of files
#
#        Rich Lafferty  
#        Thu Mar  4 02:33:30 EST 1999
#
#   Perl Power Tools -- http://language.perl.com/ppt/
# 

$^W = 1;    # -w
use strict;
use Getopt::Std;
use File::Basename;

## What's my name?
my $me = basename($0);

## Grab options
getopts ('b:c:d:f:ns', \my %opt);
   
# There's no difference between -b and -c on any unix I 
# use regularly -- it's for i18n. Thus, -n is a noop, too.
$opt{b} = $opt{c} if defined $opt{c}; 

## Byte operations
if (defined ($opt{b})) {

    my @list = split (/,/, $opt{b});

    while (<>) {
	chomp;

	foreach my $item (@list) {
	    my ($start,$end) = split (/-/, $item);
	    die "$me: invalid byte list\nType '$me' alone for usage.\n" 
		if ($start and $end and $start > $end);  # parameters overlap?

	    # change cut's list parameters to substr's parameters
	    $start--;			   # cut counts from 1, not 0
	    $start = 0 if $start < 0;          
	    $end = $start + 1 unless $item =~ /-/;
	    $start = length if $start > length;

	    if ($end) {  
		$end = length if $end > length; 
		printf ("%s", substr ($_, $start, $end - $start));
	    } else {     
		printf ("%s", substr ($_, $start));
	    }
	}
	print "\n";
    }
    exit 0;
} 

## Field operations
elsif (defined ($opt{f})) {

    my @list = split (/,/, $opt{f});
    
    my $delim = "\t";
    $delim = substr ($opt{d}, 0, 1) if defined $opt{d};

    while (<>) {
	chomp;

	# Only waste time on lines with delimiters
	if (/$delim/) {   
	    foreach my $item (@list) {
		my ($start,$end) = split (/-/, $item);
		die "$me: invalid byte list\nType '$me' alone for usage.\n" 
		    if ($start and $end and $start > $end);   # parameters overlap?
		
		# change cut's list parameters to substr's parameters
		$start--;			   # cut counts from 1, not 0
		$start = 0 if $start < 0;          
		$end = $start + 1 unless $item =~ /-/;

		my @hunk = split (/$delim/, $_);
	    
		# don't let parameters exceed number of fields
		$end = @hunk if (! $end or $end > @hunk);
		$start = @hunk if $start > @hunk;

		# If start of field is bigger than number of items, cut(1)
		# still outputs a newline -- but we won't enter the for()
		print "\n" if ($start == $end and $item eq $list[$#list]);

		for (my $i = $start; $i < $end; $i++) {
		    print $hunk[$i];
		    if ($item eq $list[$#list] and $i == $end - 1) {  # if done
			print "\n";
		    } else {
			print $delim;
		    }
		}
	    }
	} else {  # no delimiter in line
	    print "$_\n" unless $opt{"s"};
	}
    }

    exit 0;
}

## $SIG{__CLUE__}
print < list [C<-n>] [file ...]

cut C<-c> list [file ...]

cut C<-f> list [C<-d> delim] [C<-s>] [file ...]

=head1 DESCRIPTION

The B utility selects portions of each line (as specified by I)
from each I (or the standard input by default), and writes them to
the standard output.  The items specified by I can be in terms of
column position or in terms of fields delimited by a special
character. Column numbering starts from 1.

I is a comma- or whitespace-separated set of increasing numbers
and/or number ranges.  Number ranges consist of a number, a dash
('-'), and a second number and select the fields or columns from the
first number to the second, inclusive.  Numbers or number ranges may
be preceded by a dash, which selects all fields or columns from 1 to
the first number.  Numbers or number ranges may be followed by a dash,
which selects all fields or columns from the last number to the end of
the line.  Numbers and number ranges may be repeated, overlapping, and
in any order.  It is not an error to select fields or columns not
present in the input line.

=head1 OPTIONS

B accepts the following options:

=over 4

=item -b list     

The I specifies byte positions.

=item -c list     

The I specifies character positions.

=item -d string   

Use the first character of I as the field delimiter character
instead of the tab character.

=item -f list

The I specifies fields, delimited in the input by a single tab
character.  Output fields are separated by a single tab character.

=item -n

Do not split multi-byte characters.

=item -s

Suppresses lines with no field delimiter characters.  Unless
specified, lines with no delimiters are passed through unmodified.

=back

=head1 BUGS

B does not understand multibyte characters; the C<-c> and C<-b>
options function identically, and C<-n> does nothing.

=head1 STANDARDS

This B implementation is compatible with the I
implementation.

=head1 AUTHOR

The Perl implementation of B was written by Rich Lafferty,
I.

=head1 COPYRIGHT and LICENSE

This program is free and open software. You may use, copy, modify,
distribute and sell this program (and any modified variants) in any
way you wish, provided you do not restrict others to do the same.

=cut


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