perl sorting

Shell Programming and Scripting
1

I have many files that I need to sort each week. I know how to do in Unix, but for this task it appears best to do native inside an existing perl program. So, simplified, I have a file similar to the following:

Joe_________12_Main_St__A001________LX
Benny_______5_Spring____A002________LX
Will________2_A_St______A003________LX
Carl________15_X_Way____A004________LX

Fixed record format with
name in position 1
address in position 11
unique id in position 21
code in position 31

So, I already have the file open and about to close in the existing perl script - called $fileot1. I will close the file, and want to sort it.

How would I then write a few lines to sort the file descending on column 21? I have read the
@sorted = sort { lc($a) cmp lc($b) } @not_sorted
but do not know where to begin to define the parameters.

Example code is what I am looking for. Thanks.
(Sometimes, one can only understand a concept after seeing a solution.)

2

By parameters do you mean key fields. You cannot do that.
You need a subroutine:

# sort using explicit subroutine name
    sub sortsub {
	$age{$a} <=> $age{$b};	#  assumed number change this part for your needs
    }
    @sorted = sort sortsub @not_sorted;
3

>sort rawfile -t'|' -k1.21,1.30 -r
Carl________15_X_Way____A004________LX
Will________2_A_St______A003________LX
Benny_______5_Spring____A002________LX
Joe_________12_Main_St__A001________LX

and that ordered my file reverse by what is in positions 21-30.
I did this by:
(a) specifying the 'tab' or key flag as the '|' which does not exist; thus all is considered field 1
(b) said to sort on k1.21,1.30 which translated to field one positions 21 to 30
(c) and the -r put in reverse order

So in perl, I figure somehow I need to define that I want to use character positions 21-30 as the key field. Then give a command to sort on those positions.
Perhaps this needs to be its own subroutine. I do not know.

4

basic concept, May need fine tuning, I have to run but will check back later today:

@sorted = map{$_->[0]}
               sort {$b->[1] cmp $a->[1]}
               map {[$_,substr($_,20,10)]} <INPUT>;

<INPUT> is an open filehandle, change it to an array if the data is already in an array.

5

Thanks KevinADC -- what you wrote gave the basis for what follows. I know I need to handle errors on file actions. Anything else I should be thinking about here?

#! /usr/bin/perl
# start of perl
# use strict;

# set vars
$source = "rawfile";
$outfile = ">rawsorted";

# open the source file
open(SOURCE,$source);
@rawdata=<SOURCE>;
# open the output file
open(OUTFILE,$outfile);

# sort at position 21 (note the 20) for length of 10
# sort in reverse order, hence the b before a in sort{ cmp } statement
@sorted = map{$->[0]}
sort {$b->[1] cmp $a->[1]}
map {[$_,substr($,20,10)]} @rawdata;

# write the sorted file to disk
print OUTFILE @sorted;

close SOURCE;
close OUTFILE;

my rawfile stored on disk =
> cat rawfile
Joe_________12_Main_St__A001________LX
Benny_______5_Spring____A002________LX
Will________2_A_St______A003________LX
Carl________15_X_Way____A004________LX

my final sorted file =
cat rawsorted
Carl________15_X_Way____A004________LX
Will________2_A_St______A003________LX
Benny_______5_Spring____A002________LX
Joe_________12_Main_St__A001________LX

p.s. How do people get their 'code' inserted in such a way to properly indent and format? I don't see a function for that on-screen.

6

Assumes the lines of the file do not need to be filtered or validated before processing:

#! /usr/bin/perl
# start of perl
use strict;
use warnings;
# set vars
my $source = 'rawfile';
my $outfile = 'rawsorted';

# open the source file
open(SOURCE,$source) or die "Can't open $source: $!";
my @rawdata = <SOURCE>;
close SOURCE;
# open the output file
open(OUTFILE, '>', $outfile) or die "Can't open $outfile: $!";

# sort at position 21 (note the 20) for length of 10
# sort in reverse order, hence the b before a in sort{ cmp } statement
print OUTFILE map{$_->[0]}
              sort {$b->[1] cmp $a->[1]}
              map {[$_,substr($_,20,10)]} @rawdata;

close OUTFILE;

If this is a really big file it may use a lot of memory to store and process which can sometimes be a problem.

Use the code tags to display formatted code, see the FAQ section of this forum for details.