ksh88 and ksh93 both support that construct. The process substitution, <(cmd ...) is replaced with /dev/fd/n, and the first < is the usual input redirection operator.
Regards,
Alister
That's interesting. The ksh on Mac OS X Lion (Version M 1993-12-28 s+ $) says:
Quote:
-ksh: syntax error: `<(' unexpected
when given the command:
The New Kornshell Command and Programming Language book by Nolsky and Korn does say that Process Substitution using this form is a "Possible Extension" that
Quote:
is available only on versions of the UNIX system that support the /dev/fd directory for naming open files.
and OS X does support /dev/fd. It looks like someone at Apple failed to configure OS X's ksh to give us access to this feature.
Hi ,
I would like to list or sort by date and time (the files are named in day and time format) where the latest file will be placed at the bottom and the earliest file be placed at the top. Can anybody help me?
My files are named in the following manner.
EG: abc_071128_144121_data
"... (21 Replies)
Hello all,
I have a file - 12.txt
cat 12.txt
===============================================
Number of executions = 2 Total execution time (sec.ms) = 0.009883
Number of executions = 8 Total execution time (sec.ms) = 0.001270
Number of... (23 Replies)
How do you combine these ls commands so that I can have the outputs by name, time stamp, and size?
ls -al |grep name_of_file
ls -al | sort +4nr
ls -l -t
Please advise. (4 Replies)
Input file:
100%ABC2 3.44E-12 USA
A2M%H02579 0E0 UK
100%ABC2 5.34E-8 UK
100%ABC2 3.25E-12 USA
A2M%H02579 5E-45 UK
Output file:
100%ABC2 3.44E-12 USA
100%ABC2 3.25E-12 USA
100%ABC2 5.34E-8 UK
A2M%H02579 0E0 UK
A2M%H02579 5E-45 UK
Code try:
sort -k1,1 -g -k2 -r input.txt... (2 Replies)
Hi Guru,
I need some help regarding awking the output so it only show the first line (based on column) of each row.
So If column has 1, three row, then it only show the first line of that row, based on similar character in column 1. So i am trying to achieve a sort, based on column one and... (3 Replies)
Discussion started by: Junes
3 Replies
LEARN ABOUT MOJAVE
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 { $current = sort::current; }
print "$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 { $current = sort::current; }
print "$current
";
@c = sort @d;
}
perl v5.18.2 2013-11-04 sort(3pm)