List files which does not contain a string

root# grep -rL "string"

-r makes grep recursively
-L only output a filename when it does not contain “string”

[greg@localhost test123]$ ls -la
total 20
drwxrwxr-x. 2 greg greg 4096 Jun 2 11:31 .
drwx——. 18 greg greg 4096 Jun 2 11:30 ..
-rw-rw-r–. 1 greg greg 4 Jun 2 11:31 aaa.text
-rw-rw-r–. 1 greg greg 4 Jun 2 11:31 bbb.text
-rw-rw-r–. 1 greg greg 4 Jun 2 11:31 ccc.text
[greg@localhost test123]$ cat *
[greg@localhost test123]$

greg@localhost test123]$ grep -rL “123”
[greg@localhost test123]$

Vi delete commands – reference

A lot of times all people need is a quick reference, so I’ll start with a reference of vi/vim delete commands:

x – delete current character
dw – delete current word
dd – delete current line
5dd – delete five lines

d$ – delete to end of line
d0 – delete to beginning of line

delete to beginning of file

delete to end of file

Lists all files beginning with n or S followed by "-release".

ls [nS]*-release

Lists all files beginning with n or S followed by “-release” (e.g., novell-release)

oes11-34:/etc # ls -la [nS]*-release
-rw-r--r-- 1 root root 72 Jan 21 2014 novell-release
-rw-r--r-- 1 root root 69 Jun 3 2013 SuSE-release
oes11-34:/etc # cat [nS]*-release
Novell Open Enterprise Server 11 (x86_64)
VERSION = 11.2
SUSE Linux Enterprise Server 11 (x86_64)
oes11-34:/etc #

Use logger to write a messages to log files.

The basic syntax for logger is logger message. It does not require any options if you are just going to write a message to the logfile and you want to write to the default /var/log/messages at the notice level.

root# logger Added a new disk to a machine

You can see a message in /var/log/message file. Also you can run this command with option -s Log the message to standard error, as well as the system log.

root# logger -s Added a new disk to a machine

Testing whether a string is null.

Testing whether a string is null.

# Testing null strings and unquoted strings,
#+ but not strings and sealing wax, not to mention cabbages and kings . . .

# Using if [ … ]

# If a string has not been initialized, it has no defined value.
# This state is called “null” (not the same as zero!).

if [ -n $string1 ] # string1 has not been declared or initialized.
echo “String “string1″ is not null.”
echo “String “string1″ is null.”
fi # Wrong result.
# Shows $string1 as not null, although it was not initialized.

Continue reading “Testing whether a string is null.”

Tarballs benchmark – gz, bz2 and xz.

Directory used for this benchmark: test_tarball 189M in size. The directory contains /var/log files.

OS: Ubuntu 12.04LTS
CPU: Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz
RAM: 2 x 4096MB DDR3 1333MHz
HDD: Hitachi HTS72323

tar cvzf tarball.tar.gz test_tarball/
Size of tar.gz tarball: 22M
Compression time: 0m3.926s

tar cvjf tarball.tar.bz2 test_tarball/
Size of tar.bz2 tarball: 19M
Compression time: 0m38.924s

tar cvJf tarball.tar.xz test_tarball/
Size of tar.xz tarball: 18M
Compression time: 0m57.988s

It seems that it does not make sense for use .xz tarball for small size files.