Hello shabird,

it gives the length of the string but it also counts the enter key

You should chomp the string to remove the trailing newline before finding the length.

the order is not sorted although i have used to sort function for that.

By default, sort sorts in lexicographical order, so 100 comes before 90 because 1 comes before 9. To sort numerically, do this:

my @array = sort { $a <=> $b } $frstLength, $scndLength, $trdLength, $
+frthLength;
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You should also begin your script with use strict;, which forces you to declare each variable with my. (This is a good thing! It will save you a lot of debugging time in the long run.)

Hope that helps,

Hello Athanasius Thank you for your explanation it helped but can you please explain what does this code { $a <=> $b } means?

Athanasius uses the sort BLOCK LIST syntax of sort. The block is {$a <=> $b}. Blocks are documented in Basic BLOCKS. The operator (<=>) is described in Equality Operators. The package variables $a and $b are described through out the documentation for sort. The short answer is that this block tells sort to sort the list in numerical order rather than the default lexical order.
Bill

"push" adds stuff into the back of an array, while "pop" removes it.
"chomp" deletes the last "line ending" character(s), if they exist.
The "sort" uses the "Numeric compare" operator "<=>" to compare the length, and returns each item in the sorted array as "$_", which is then printed along with a newline (\n).
The sort BLOCK using "$a <=> $b" is a common/canonical perl idiom for numeric sort. Just accept that till you research it deeper. "$_" is commonly used as a "temporary" variable when the programmer is too lazy to give it a name.

use strict;
use warnings;

my @seq; # DNA sequence strings

do{
    print "Please enter DNA sequence (END to finish):";
    push @seq , $_=<STDIN>;  # First, assign whatever is read into $_,
+ then append it to @seq
  } until $_ eq "END\n";

pop @seq;   # Remove the extra "END\n" entry;
chomp @seq; # Remove line endings on each entry

print "$_\n" 
  for  sort {length $a <=> length $b} @seq;
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If you really want a fixed number of entries then this variation of NewWalla's reply may help.

use strict;
use warnings;

my @seq; # DNA sequence strings

for my $count (1 .. 4) {
    print "Please enter DNA sequence $count:";
    push @seq, scalar <STDIN>;
}

chomp @seq; # Remove line endings on all entries

printf "%2d: %s\n", length $_, $_ for  sort {length $a <=> length $b} 
+@seq;
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Prints (for some arbitrary input):

Please enter DNA sequence 1:asdf
Please enter DNA sequence 2:zvasdfasf
Please enter DNA sequence 3:asd
Please enter DNA sequence 4:asdfasg
 3: asd
 4: asdf
 7: asdfasg
 9: zvasdfasf
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You can visit PerlDoc to find out what scalar does.

Here's another approach. In addition to collecting user input, it tries to control (the user can exit the collection loop early using loop control) and validate (using regexes or regular expressions — see perlre, perlretut, perlreref and perlrequick for info on these) the input. Any upper- or lower-case alpha character is accepted as a "DNA" character, but you can alter the validation regex to refine this for your application. It also has some debug statements; take them out for final use. :)

Script: get_seqs_1.pl:

Win8 Strawberry 5.8.9.5 (32)  Sun 09/20/2020 22:47:03
C:\@Work\Perl\monks\shabird
>perl get_seqs_1.pl
please enter DNA sequences:
  first sequence: dddddd
  secundus sequence: sss
  third sequence: ffffffffff
  4th sequence: gggggg
$VAR1 = {
          'first' => {
                       'len' => 6,
                       'seq' => 'dddddd'
                     },
          'secundus' => {
                          'len' => 3,
                          'seq' => 'sss'
                        },
          '4th' => {
                     'len' => 6,
                     'seq' => 'gggggg'
                   },
          'third' => {
                       'len' => 10,
                       'seq' => 'ffffffffff'
                     }
        };
valid entered sequences in order of prompt:
  first: dddddd (6)
  secundus: sss (3)
  third: ffffffffff (10)
  4th: gggggg (6)
valid entered sequences in order of increasing length:
  secundus: sss (3)
  first: dddddd (6)
  4th: gggggg (6)
  third: ffffffffff (10)
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