I was confused with what the
was doing, but your explanation has helped with this, although I still don't understand what the 4 before the comma is doing.
"sort" interprets lines as "fields" being delimited by "delimiters". Per default this delimiter is whitespace.
Per default "sort" sorts on field 1, then on field 2, then field 3 and so on until the end of the line. Lines with equal values of field 1 will be sorted on the contents of field 2, lines with equal fields 1 & 2 sorted on field 3, etc. If you want another field or part of it) as the primary key you will have to use the "-k" option and a field number. But this leaves the question, how lines with equal sort keys should be handled.
Per default sort will use the fields starting with field 1 as secondary sort key in this case:
will produce the sort order: f4, f1, f2, f3, f4, ....
By defining, where the key should end you can change this default behavior:
Sorting occurs exclusively on field 4, because the ",4" says the ending of the sort key is field 4.
The man page of sort should explain this in greater detail.
Hi,
Could you please explain me the below statement -- phrase wise.
sed -e :a -e '$q;N;'$cnt',$D;ba' abc.txt > xyz.txt
if suppose $cnt contains value: 10
it copies last 9 lines of abc.txt to xyz.txt
why it is copying last 9 rather than 10.
and also what is ba and $D over there in... (4 Replies)
Hello everyone,
I found this command line in a website:
perl -pi.bak -we's/\z/Your new line\n/ if $. == 2;' your_text_file.txt
With this command line you can insert a new line anywhere you want in a text without overwriting what's in it.
-p causes perl to assume a loop around your... (4 Replies)
Hi to all.
I'm trying to sort this with the Unix command sort.
user1:12345678:3.5:2.5:8:1:2:3
user2:12345679:4.5:3.5:8:1:3:2
user3:12345687:5.5:2.5:6:1:3:2
user4:12345670:5.5:2.5:5:3:2:1
user5:12345671:2.5:5.5:7:2:3:1
I need to get this:
user3:12345687:5.5:2.5:6:1:3:2... (7 Replies)
sed '$!N; /^\(.*\)\n\1$/!P; D'
i found this file which removes duplicates irrespective for sorted or unsorted file. keep first occurance and remove the further occurances.
can any1 explain how this is working..
i need to remove duplicates following file. duplicate criteria is not the... (3 Replies)
can anyone please tell me what does this expression means , i am under probation and need some explanation :)
$AUDIT_DIR -type f -mtime +$AUDIT_EXPIRE \ -exec rm {} > /dev/null 2>&1 \;
AUDIT_DIR="/var/log/"
AUDIT_EXPIRE='30'
Please use code tags! (4 Replies)
Hi All
I ran a script in Linux.
In the script i have lines like
&& echo "Failed: Missing ${CM_ENV_FILE} \n" && return 1
. ${CM_ENV_FILE}
Where CM_ENV_FILE = /data/ds/dpr_ebicm_uat//etl/cm3_0/entities/BBME/parameters/cm.env
But its taking this path... (1 Reply)
I tried to use sort utility and typed sort --help, read one of lines; its -k option, and part of it:
I am really not getting it
Anyone do me a useful favor to save me out of my ignorance ?
Please use correct tags as required by forum rules! (1 Reply)
Hi Folks,
I am struggling to understand nawk command which was used by another developer.
Can you please explain what each character or string is doing here below:
if ; then (3 Replies)
Discussion started by: kirans.229
3 Replies
LEARN ABOUT SUSE
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 v5.12.1 2010-04-26 sort(3pm)