You got it.
You probably already know the best way to learn is to log on and play around on the computer. You're right if only two people are on (you and the admin) that you can't really test "who" very well. In that case, you can create a little test file, and do some experiments, such as:
I used "echo" to make the test.txt file. If you know how to use a Unix editor, of course use the editor instead.
With the test file, you can try out different sort options, as you are already doing with -r option.
Quote:
I am not really sure why this order of who and sort works.
Is it because you need to run who first so the sort takes
the input from the other command (who)?
Yes, that is exactly right! "who" produces the output, the "raw materials". The output from "who" enters the pipe. On the other side of the pipe, "sort" reads its input. The output from "sort" is what you finally see.
"who" does not expect any input, so it would not make sense to put "who" on the right-hand side of the pipe. "sort" HAS to have input, or have a file specified for it to operate upon. In the examples above, I showed three simple ways sort can get input (sort file, | sort, and sort < file).
Quote:
P.S. I am doing a small grading program for this same lab as well.
I will post my results later tonight. Didn't post here because I had
not yet tried anything. Should I open a new thread or post here?
Hello all,
I have a test file that has the format:
.....
O
3.694950 -.895050 1.480000
O
5.485050 .895050 1.480000
Ti
-4.590000 4.590000 2.960000
Ti
-2.295000 ... (5 Replies)
hello folks
i have a file that have data like
/test/aa/123
/test/aa/xyz
/test/bb/xyz
/test/bb/123
in above lines i just wants to grep "aa" and "bb".
Thanks,
Bash (4 Replies)
can someone help me in the awk part...little confuse on that part.
The problem is this: what input each utility gets and what it does with data and what output is provides to the next utility)
history | awk '{a++}END{for(i in a){print a " " i}}' | sort -rn | grep '^'
Thanks (4 Replies)
Hi Expert,
Kindly request for your expertise in this matter.
I have below output:
12.125.124.173,xx1.common.com
12.125.124.174,xx2.common.com
12.125.124.175,xx3.common.com
12.125.124.176,
12.125.124.177,
12.125.124.178,
12.125.124.179,xx4.common.com
12.125.124.180,xx5.common.com... (8 Replies)
for example, I have a text file in random content inside, maybe something like this.
234234
54654
123134
467456
24234234
7867867
23424
568567if I run this command
cat "filename.txt" | sort -n | grep "^467456$" -A 1 -B 1the result is
234234
467456
568567is it possible to do this command... (2 Replies)
Hi,
Trying to sort grep result based on timestamp of the filename.
I have the following result and want to sort them on timestampgrep -i 'ERROR' *log*2013*
s_m_xxx_xxx_xxx_xxx_xxxx.log.20130906092431:TRANSF_1_1_1> DBG_21216 Finished transformations for Source Qualifier . Total errors ... (5 Replies)
1. The problem statement, all variables and given/known data:
So i'll probably get told off for this but I have a few problems and rather than clog up the whole forum I'll post them here. Please bare in mind I am a complete novice when it comes to all this and so if you help please treat me like a... (4 Replies)
1. The problem statement, all variables and given/known data:
Please bare in mind I am a complete novice to this and have very very basic knowledge so please keep any answers as simple as possible and explain in terms I will understand ahha :):)
I have a text file of names and test scores... (1 Reply)
Hi Gurus,
I have two big files. I need to compare the different. currently, I am using
sort file1 > file1_temp;
sort file2 > file2_tmp
diff file1_tmp file2_tmp
I can use command
grep -v -f file1 file2
just wondering which way is fast to compare two big files.
Thanks... (4 Replies)
Discussion started by: ken6503
4 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)