sort alphabetically whole word in first array position - perl

Question

I have a file with values separated by pipe |
input:
car tree alfa young|salt brick|23223|
emilia jack albert| way to go|56566|
I'm trying to sort first column alphabetically and write sorted file out.
result:
alfa car tree young|salt brick|23223|
albert emilia jack| way to go|56566|
What I have tried:
can sort first array position but cant write out all file content.
$filename = 'test.dat';
open (INPUT,"$filename");
open (OUTPUT,">out.dat");
while (<INPUT>)
{
#array = split('\|');
#arr = split(' ',$array[0]);
$,=" ";
print OUTPUT sort #arr,"\n";
}
close (INPUT);
close (OUTPUT);
sorts everything in each line.
$filename = 'test.dat';
open (INPUT,"$filename");
open (OUTPUT,">out.dat");
while (<INPUT>)
{
#arr = split(' ');
$,=" ";
print OUTPUT sort #arr,"\n";
}
close (INPUT);
close (OUTPUT);

Answer 1

Your programs will be far more flexible if you move away from the idea of hard-coding file names in your code. It's a much better idea to read from STDIN and write to STDOUT whenever possible. That's what this code does.
#!/usr/bin/perl
use strict;
use warnings;
while (<>) {
# Split the record into the first field (the one we want to sort)
# and everything else.
my ($first, $rest) = split /\|/, $_, 2;
# Split the first record into words
my #words = split /\s+/, $first;
# Sort #words and then join the line back together and print it.
print join(' ', sort #words), "|$rest";
}
If we store this program in a file called reorder, we can then run it from a command-line prompt like this:
$ ./reorder < test.dat > out.dat
We avoid having to open any filehandles (the operating system does it for us) and we don't need to change the program if the filenames ever change.

Answer 2

perl -pe 's/^([^|]+)/#a = sort split ' ', $1; "#a";/e' myfile

Answer 3

After you've split the line into an array
my #ary = split '\|';
you need to split the first element, sort the list, and join it back
my $first = join ' ', sort split ' ', shift #ary;
where shift removes (and returns) the first element.
Then build the string back
my $new_string = join '|', $first, #ary;
This can be done without temporary variables. The last two steps can be done in one statement, and all of it right in a print statement.
Comments
Please always start your programs with use warnings; and use strict;
Use three-argument form of open
open my $fh, '<', $file or die "Can't open $file: $!";
and so use lexical filehandles ($fh), not bareword (typeglobs, FH).
Don't quote things that don't need to be quoted -- even errors can result! See What's wrong with always quoting (perlfaq4), for instance. Thanks to Sinan Ünür for the comment.
You can also do it with a regex
$line =~ s/(.*?)\|/join(" ", sort split " ", $1).q(|)/e;
This captures the first field (up to the pipe), and runs the above code on it, courtesy of /e modifier which makes replacement part be evaluated as code.
We needed to also match the pipe and then put it back. This can be avoided using lookahead
$line =~ s/(.*?)(?=\|)/join(' ', sort split ' ', $1)/e;
which only asserts that the pattern inside (?=...) is there, without consuming it.

Answer 4

Your first bit of code is so very close to being right. You're only outputting the first column though - you need to print out the contents of #array. If you replace the first element of #array with the sorted results, then you can just write it out like this.
#array = split('\|');
$array[0] = join(" ",sort split(' ',$array[0]));
print OUTPUT join("|",#array),"\n";