Unix and Linux Tips

Rabu, 07 Juli 2010

Unix Tip: EFFICIENT COMMANDS

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UNIX GURU UNIVERSE
UNIX HOT TIP

Unix Tip 3074 - July 7, 2010

http://www.ugu.com/sui/ugu/show?tip.today

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EFFICIENT COMMANDS

I cringe anytime I see someone code
inefficiently. Here are three of the
most common mistakes, followed by a
better way to do the same thing.

Bad: cat somefile | grep something
Better: grep something somefile
Why: You're running one program (grep) instead of two (cat and grep).

Bad: ps -ef | grep something | grep -v grep
Better: ps -ef | grep [s]omething
Why: You're running two commands (grep) instead of three (ps
and two greps).

Bad: cat /dev/null > somefile
Better: > somefile
Why: You're running a command (cat) with I/O redirection,
instead of just redirection.

Although the bad way will have the
same result, the good way is far
faster. This may seem trivial, but
the benefits will really show when
dealing with large files or loops.

Regards.

This tip generously supported by: sec@nbnet.nb.ca

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Selasa, 06 Juli 2010

Unix Tip: TOO MANY FILES AROUND

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UNIX GURU UNIVERSE
UNIX HOT TIP

Unix Tip 3073 - July 6, 2010

http://www.ugu.com/sui/ugu/show?tip.today

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TOO MANY FILES AROUND

In case there are too many
files in a particular
directory. When the
following is executed:

$grep "ABC" *

And it fails saying with

ksh: /usr/bin/find: 0403-027 The parameter list is too long.

what would you do?

Well you can do the following:

$ls |xargs grep "ABC"

-----
Puneet Agarwal
This tip generously supported by: puneeta@delhi.tcs.co.in

Unix Guru Universe - www.ugu.com - tips@ugu.com - Copyright 1994-2001
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Senin, 05 Juli 2010

Unix Tip: EXTRACT RELATIVE FROM ABSOLUTE

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UNIX GURU UNIVERSE
UNIX HOT TIP

Unix Tip 3072 - July 5, 2010

http://www.ugu.com/sui/ugu/show?tip.today

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EXTRACT RELATIVE FROM ABSOLUTE

Ever had a tar archive which
was tarred up with an absolute
path, but you need to untar
it to a relative location?

There is an easy way to do
this using the "pax" command.
Note: Not available on all
flavors.

Firstly, copy the archive to
the relative location in
which you wish to untar it.

Then, execute the following
command:

pax -r -s ',^/,,' -f file.tar

The contents of file.tar will now
be in the $CWD.

Unix Guru Universe - www.ugu.com - tips@ugu.com - Copyright 1994-2001
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Minggu, 04 Juli 2010

Unix Tip: BELIEVE THE VENDOR?

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UNIX GURU UNIVERSE
UNIX HOT TIP

Unix Tip 3071 - July 4, 2010

http://www.ugu.com/sui/ugu/show?tip.today

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BELIEVE THE VENDOR?

Don't always feel that you should
believe the vendor.

Patches, vendor recommendations,
and out-sourced hardware support
engineers are some of the leading
causes of breaking a system. There
are times when you know your systems
better then they do.

If something doesn't feel right or
doesn't feel right , don't let them
do it. Ask a lot of questions and let
them know what your experience is.

Cover yourself first, run full
backups, ask them if the have ever
done the task before. Ask them to
confirm the procedure with a back
level support person.

Many times vendors will out-source
the hardware support to third party
companies. When this happens, you
may never get the same person twice,
nor know what experience he has on
your system.

If one of the first things a support
person does is ask where a phone is,
it is almost a guarantee that he will
lack the knowledge he should have and
will need to rely on someone else for
answer. While we all have much work
to do, DON'T LEAVE this type of person
alone with your systems.

Trust no one, it is you job and
reputation on the line.

-Kirk Waingrow

The tip is supported by: kirk@ugu.com

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Sabtu, 03 Juli 2010

Unix Tip: REMOVING CORES CONDITIONALLY

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UNIX GURU UNIVERSE
UNIX HOT TIP

Unix Tip 3070 - July 3, 2010

http://www.ugu.com/sui/ugu/show?tip.today

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REMOVING CORES CONDITIONALLY

To find and remove core files
conditionally:

PROMPT> find ~ -name core -exec file {} \; -exec rm -i {} \;

The File will show which
executable the core file is
for and the -i option to rm
will allow you to choose
weather to delete it or not.

################# EXAMPLE ###############################
PROMPT> find ~ -name core -exec file {} \; -exec rm -i {} \;
/my/home/core: ELF 32-bit LSB core file of 'netscape-commun'
(signal 3), Intel 8
rm: remove `/my/home/core'? y

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Jumat, 02 Juli 2010

Unix Tip: INSERTING LINES WITHIN SCRIPTS

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UNIX GURU UNIVERSE
UNIX HOT TIP

Unix Tip 3069 - July 2, 2010

http://www.ugu.com/sui/ugu/show?tip.today

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INSERTING LINES WITHIN SCRIPTS

If you want to insert a line
at the top (or anywhere for
that matter) of a file within
a shell script, use the ed editor.

EXAMPLE:

string="hello"
ed << EOF
e any_file
1i
${string}

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Kamis, 01 Juli 2010

Unix Tip: Rename files script

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UNIX GURU UNIVERSE
UNIX HOT TIP

Unix Tip 3068 - July 1, 2010

http://www.ugu.com/sui/ugu/show?tip.today

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Rename files script

If you want to rename files
in a directory then you can
use the following perl
script....

#!/usr/bin/perl
# rename: renames files according to the expr given on the command line.
# The expr will usually be a 's' or 'y' command, but can be any valid
# perl command if it makes sense. Takes a list of files to work on or
# defaults to '*' in the current directory.
# e.g.
# rename 's/\.flip$/.flop/' # rename *.flip to *.flop
# rename s/flip/flop/ # rename *flip* to *flop*
# rename 's/^s\.(.*)/$1.X/' # switch sccs filenames around
# rename 's/$/.orig/' */*.[ch] # add .orig to your source files in */
# rename 'y/A-Z/a-z/' # lowercase all filenames in .
# rename 'y/A-Z/a-z/ if -B' # same, but just binaries!
# rename chop *~ # restore all ~ backup files

use Getopt::Std;
my ($subst, $name);

if (!&getopts("nfq") || $#ARGV == -1) {
die "Usage: rename [-fnq] <perl expression> [file file...]
-f : Force the new filename even if it exists already
-n : Just print what would happen, but don't do the command
-q : Don't print the files as they are renamed
e.g. : rename 's/\.c/.c.old/' *
rename -q 'y/A-Z/a-z/' *\n";
}

$subst = shift; # Get perl command to work on
@ARGV = <*> if $#ARGV < 0; # Default to complete directory

foreach $name (@ARGV) {
$_ = $name;
eval "$subst;";
die $@ if $@;
next if -e $_ && !$opt_f; # Skip if the file exists if asked to.
mext if $_ eq $name;
if ($opt_n) {
print "mv $name $_\n";
next;
}
print "mv $name $_\n" if !$opt_q;
rename($name,$_) or warn "Can't rename $name to $_, $!\n";
}

Put the script called rename in /usr/local/bin. Make sure
/usr/local/bin is in your $PATH for convenience.

This tip generously supported by: dave.ruddle@siemens.co.uk

Unix Guru Universe - www.ugu.com - tips@ugu.com - Copyright 1994-2001
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