i'm halfway into my script and realize i may need to use an associative array (a hash, i guess they are called in Perl). i'm fairly new to Perl and don't know how to use them correctly.
i have some files in a directory. each file contains a number in a specific place in it's header. what i would... (4 Replies)
Hello,
I have a page where multiple fields and their values are displayed. But I am able to sort only a few fields. When I looked into the issue, it is seen that the for each row of info , an unique id is generated and id.txt is generated and saved. Only those fields which are inside that id.txt... (3 Replies)
I have an array full of string values that need to be sorted, but if a value starts with (regex) 0^ it should be at the beginning of the array. Otherwise the array should be sorted normally using ascii sort.
Please help me create the sub to pass to the sort function. (7 Replies)
Hi All,
I have an array in perl as @match = (201001,201002,201001,201002);
I am trying to sort this array as
@match = sort(@match);
print "@match";
I dont see the output sorted any answers
I also tried another way, but still the results are not sorted
foreach my $match (sort { $a... (2 Replies)
Hi,
I have a file in this format:
a b c d e
a b c d e
a b c d e
i need perl script to sort 2nd column in alphabatical order
The script i use is
#!/usr/bin/perl
my @words=<>;
foreach(sort mysort @words) {
print; (4 Replies)
Good morning!!
Im trying to practice withe Perl and sorting variables is not going good at all!
#!/usr/bin/perl
$username = $ENV {'LOGNAME'};
print "Hello, $username\n";
I want to add sort and 'mail' and 'home'. This below is what I have came up with,but of course its not working.
... (5 Replies)
I have a file abc.txt which contains data in th following format
abc,23
hgfh,87
tweg,89
jdfjn,74
I want to sort on the basis of column (the second one). It should be numerical sort.
output should be
abc,23
jdfjn,74
hgfh,87
tweg,89
I know how to do it in unix. I need a PERL code (1 Reply)
Hi all,
Not sure if this should be in the programming forum, but I believe it will get more response under the Shell Programming and Scripting FORUM.
Am trying to write a customized df script in Perl and need some help with regards to using arrays and file handlers.
At the moment am... (3 Replies)
I have a directory of backup files.
named like this:
ldap.data.04-06-2012.tar
ldap.data.03-06-2012.tar
ldap.data.02-06-2012.tar
ldap.data.01-06-2012.tar
ldap.data.31-05-2012.tar
ldap.data.30-05-2012.tar
ldap.data.29-05-2012.tar
ldap.data.28-05-2012.tar
ldap.data.27-05-2012.tar... (6 Replies)
Hey guys,
I have started to learn perl recently because of a position I took. They want me to master perl and I've been reading books and practicing myself.
Basically I,m having my perl script run through a text pad and give the output in a special way
e.g
input
deviceconfig {
... (5 Replies)
Discussion started by: zee3b
5 Replies
LEARN ABOUT CENTOS
sort
sort(3pm) Perl Programmers Reference Guide sort(3pm)NAME
sort - perl pragma to control sort() behaviour
SYNOPSIS
use sort 'stable'; # guarantee stability
use sort '_quicksort'; # use a quicksort algorithm
use sort '_mergesort'; # use a mergesort algorithm
use sort 'defaults'; # revert to default behavior
no sort 'stable'; # stability not important
use sort '_qsort'; # alias for quicksort
my $current;
BEGIN {
$current = sort::current(); # identify prevailing algorithm
}
DESCRIPTION
With the "sort" pragma you can control the behaviour of the builtin "sort()" function.
In Perl versions 5.6 and earlier the quicksort algorithm was used to implement "sort()", but in Perl 5.8 a mergesort algorithm was also
made available, mainly to guarantee worst case O(N log N) behaviour: the worst case of quicksort is O(N**2). In Perl 5.8 and later,
quicksort defends against quadratic behaviour by shuffling large arrays before sorting.
A stable sort means that for records that compare equal, the original input ordering is preserved. Mergesort is stable, quicksort is not.
Stability will matter only if elements that compare equal can be distinguished in some other way. That means that simple numerical and
lexical sorts do not profit from stability, since equal elements are indistinguishable. However, with a comparison such as
{ substr($a, 0, 3) cmp substr($b, 0, 3) }
stability might matter because elements that compare equal on the first 3 characters may be distinguished based on subsequent characters.
In Perl 5.8 and later, quicksort can be stabilized, but doing so will add overhead, so it should only be done if it matters.
The best algorithm depends on many things. On average, mergesort does fewer comparisons than quicksort, so it may be better when
complicated comparison routines are used. Mergesort also takes advantage of pre-existing order, so it would be favored for using "sort()"
to merge several sorted arrays. On the other hand, quicksort is often faster for small arrays, and on arrays of a few distinct values,
repeated many times. You can force the choice of algorithm with this pragma, but this feels heavy-handed, so the subpragmas beginning with
a "_" may not persist beyond Perl 5.8. The default algorithm is mergesort, which will be stable even if you do not explicitly demand it.
But the stability of the default sort is a side-effect that could change in later versions. If stability is important, be sure to say so
with a
use sort 'stable';
The "no sort" pragma doesn't forbid what follows, it just leaves the choice open. Thus, after
no sort qw(_mergesort stable);
a mergesort, which happens to be stable, will be employed anyway. Note that
no sort "_quicksort";
no sort "_mergesort";
have exactly the same effect, leaving the choice of sort algorithm open.
CAVEATS
As of Perl 5.10, this pragma is lexically scoped and takes effect at compile time. In earlier versions its effect was global and took
effect at run-time; the documentation suggested using "eval()" to change the behaviour:
{ eval 'use sort qw(defaults _quicksort)'; # force quicksort
eval 'no sort "stable"'; # stability not wanted
print sort::current . "
";
@a = sort @b;
eval 'use sort "defaults"'; # clean up, for others
}
{ eval 'use sort qw(defaults stable)'; # force stability
print sort::current . "
";
@c = sort @d;
eval 'use sort "defaults"'; # clean up, for others
}
Such code no longer has the desired effect, for two reasons. Firstly, the use of "eval()" means that the sorting algorithm is not changed
until runtime, by which time it's too late to have any effect. Secondly, "sort::current" is also called at run-time, when in fact the
compile-time value of "sort::current" is the one that matters.
So now this code would be written:
{ use sort qw(defaults _quicksort); # force quicksort
no sort "stable"; # stability not wanted
my $current;
BEGIN { $current = print sort::current; }
print "$current
";
@a = sort @b;
# Pragmas go out of scope at the end of the block
}
{ use sort qw(defaults stable); # force stability
my $current;
BEGIN { $current = print sort::current; }
print "$current
";
@c = sort @d;
}
perl v5.16.3 2013-03-04 sort(3pm)