Arguments are the things you feed into a program, like so:
argument 1 would be 1, and so forth.
'echo' doesn't actually understand what * means. The shell translates * into a list of files for you, before the program is run. So you can use * anywhere a list of file arguments makes sense!
ls on the other hand, reads filenames by itself. It also has options to sort them (-t means sort by time ), and print extended information ( -l ) which * cannot do.
I'm sure this is an easy one but I can't seem to get it working. Given the following:
for oldName in `ls *.JPG` ;do
newName=<confusion here. how to make sed perform 's/.JPG/_thumb.JPG/g' operation on $oldName>
done
Could someone show me what I'm doing wrong?
Thanks
Ken (1 Reply)
Hi all,
I have a directory have all of the .stat and .dat file :
they are is a pipe separate flat file.
Example:
log-20061202.stat contain 1st line and last line of log-20061202.dat with record count of that day.
Example:
Total record = 240
Tom|02-12-2006|1600 W.Santa... (18 Replies)
Basically I have a shell script and i want to search the computer for a folder and if that folder exists i want to take some action. Not sure exactly how to do this most efficiently.
Not very experienced....any help would be appreciated. (1 Reply)
Hello everybody...
I'm a Unix newbie and i just got this task at work to figure out what's wrong with a daily script my team is using.
The idea behind the script is that it takes the day before in a yyyymmdd format, find files with that date in a specific directory and executes an (irrelavant)... (4 Replies)
Q1>How do i read and write to file in shell script. Here is what i want let's assume the filename as "file1"
Read file1
Check the content of file1 which can be either "0" or "1"
if(content == 0)
{
execute a command
}
flush file1(remove all contents in it)
write "1" in to... (5 Replies)
My problem looks like it should have a simple solution but it seems that after many days of research I cannot find a good solution. What I have is an input file that contains lines of information. What I need is to extract specific information from that file. What I know is that somewhere in the... (2 Replies)
script is:
dirname= "$(date +%b%d)_$(date +%H%M)"
mkdir $dirname
should create a directory named Nov4_
Instead I get the following returned:
root@dchs-pint-001:/=>./test1
./test1: Nov04_0736: not found.
Usage: mkdir Directory ...
root@dchs-pint-001:/=>
TOO easy, but what am I... (2 Replies)
Can someone help me write this shell script?
I am completely new to shell and as a fun task my uncle has challenged me a problem (out of all other people). Basically, all he wants me to do is to create backup file in a folder that is named “disables.”
This is what he said: create a shell script... (0 Replies)
Hello all,
I want to write a shell script to list the contents of a directory and number them and write them to a file.
For example, if I have a directory temp and the contents of the directory are alpha, beta and gamma. I want to write these filenames to a file "test" in a numbered manner.
... (7 Replies)
Hi,
I am totally a newbie to any programming languages and I just started an entry level job in an IT company. One of my recent tasks is to create a script that is able to show the log file of linux service (i.e. ntpd service)
lets say, if I run my script ./test.sh, the output should be... (3 Replies)
Discussion started by: xiaogeji
3 Replies
LEARN ABOUT REDHAT
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 $current = sort::current(); # identify prevailing algorithm
DESCRIPTION
With the "sort" pragma you can control the behaviour of the builtin "sort()" function.
In Perl versions 5.6 and earlier the quicksort algorithm was used to implement "sort()", but in Perl 5.8 a mergesort algorithm was also
made available, mainly to guarantee worst case O(N log N) behaviour: the worst case of quicksort is O(N**2). In Perl 5.8 and later, quick-
sort defends against quadratic behaviour by shuffling large arrays before sorting.
A stable sort means that for records that compare equal, the original input ordering is preserved. Mergesort is stable, quicksort is not.
Stability will matter only if elements that compare equal can be distinguished in some other way. That means that simple numerical and
lexical sorts do not profit from stability, since equal elements are indistinguishable. However, with a comparison such as
{ substr($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 compli-
cated 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
This pragma is not lexically scoped: its effect is global to the program it appears in. That means the following will probably not do what
you expect, because both pragmas take effect at compile time, before either "sort()" happens.
{ use sort "_quicksort";
print sort::current . "
";
@a = sort @b;
}
{ use sort "stable";
print sort::current . "
";
@c = sort @d;
}
# prints:
# quicksort stable
# quicksort stable
You can achieve the effect you probably wanted by using "eval()" to defer the pragmas until run time. Use the quoted argument form of
"eval()", not the BLOCK form, as in
eval { use sort "_quicksort" }; # WRONG
or the effect will still be at compile time. Reset to default options before selecting other subpragmas (in case somebody carelessly left
them on) and after sorting, as a courtesy to others.
{ 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
}
# prints:
# quicksort
# stable
Scoping for this pragma may change in future versions.
perl v5.8.0 2002-06-01 sort(3pm)