UNIX for Dummies Questions & Answers

#!/usr/bin/env bash

# @(#) s1       Demonstrate arbitrary ordering.

set -o nounset
echo

debug="echo"
debug=":"

SEQ=/usr/bin/seq

## Use local command version for the commands in this demonstration.

version bash $SEQ

echo

# 2,5,3,4,1
cat >data1 <<EOF
Expected last.
Expected first.
Expected third.
Expected fourth.
Expected second.
EOF

# See discussion of bash arrays at:
# http://www.tldp.org/LDP/abs/html/arrays.html

oldIFS="$IFS"
IFS="
"
array=( $(cat data1) )
IFS="$oldIFS"

last=$(( ${#array[*]} ))
echo " Input data:"
for i in $( $SEQ 1 $last )
do
  j=$(( i-1 ))
  $debug " printing element $j"
  echo ${array[${j}]}
done

echo
echo " Ordered data:"
for i in 2 5 3 4 1
do
  j=$(( i-1 ))
  $debug " printing element $j"
  echo  "${array[${j}]}"
done

exit 0

% ./s1

GNU bash, version 2.05b.0(1)-release (i386-pc-linux-gnu)
seq (coreutils) 5.2.1

 Input data:
Expected last.
Expected first.
Expected third.
Expected fourth.
Expected second.

 Ordered data:
Expected first.
Expected second.
Expected third.
Expected fourth.
Expected last.

awk '
   BEGIN { split("2 5 3 4 1", my_sort) }
         { rows[NR]=$0 }
   END   { for (row in rows) print rows[my_sort[++i]] }
' input_file.txt

#!/usr/bin/perl

# @(#) p1       Demonstrate arbitrary ordering.

use warnings;
use strict;

my ($debug);
$debug = 1;
$debug = 0;

my ( @content, @order, $t1 );

# Define ordering.

@order = qw/ 2 5 3 4 1 /;
print STDERR " Output order = '@order'\n" if $debug;
my ($order_length) = scalar @order;

# Read entire file into an array.

@content = <>;

print "\n";
print " Input data:\n";
print @content;
my ($lines) = scalar @content;

if ( $order_length > $lines ) {
  warn(" Lines in file less than ordering, output will be incomplete.\n");
}

# Print according to specified order.

print "\n";
print " Output result:\n";
foreach my $i (@order) {
  if ( defined( $t1 = $content[ $i - 1 ] ) ) {
    print $t1;
  }
  else {
    print STDERR " ( Element $i skipped.)\n";
  }
}

print STDERR " ( Lines read: $lines )\n";

exit(0);

% ./p1 data1

 Input data:
Expected last.
Expected first.
Expected third.
Expected fourth.
Expected second.

 Output result:
Expected first.
Expected second.
Expected third.
Expected fourth.
Expected last.
 ( Lines read: 5 )