Source: http://bashcurescancer.com/10-linux-commands-youve-never-used.html
# pgrep, instead of:
# ps -ef | egrep '^root ' | awk '{print $2}'
1
2
3
4
5
20
21
38
39
...
You can do this:
# pgrep -u root
1
2
3
4
5
20
21
38
39
...
# pstree, list the processes in a tree format. This can be VERY useful when
working with WebSphere or other heavy duty applications.
# pstree
init-+-acpid
|-atd
|-crond
|-cups-config-dae
|-cupsd
|-dbus-daemon-1
|-dhclient
|-events/0-+-aio/0
| |-kacpid
| |-kauditd
| |-kblockd/0
| |-khelper
| |-kmirrord
| `-2*[pdflush]
|-gpm
|-hald
|-khubd
|-2*[kjournald]
|-klogd
|-kseriod
|-ksoftirqd/0
|-kswapd0
|-login---bash
|-5*[mingetty]
|-portmap
|-rpc.idmapd
|-rpc.statd
|-2*[sendmail]
|-smartd
|-sshd---sshd---bash---pstree
|-syslogd
|-udevd
|-vsftpd
|-xfs
`-xinetd
# bc is an arbitrary precision calculator language. Which is great. I found
it useful in that it can perform square root operations in shell scripts.
expr does not support square roots.
# ./sqrt
Usage: sqrt number
# ./sqrt 64
8
# ./sqrt 132112
363
# ./sqrt 1321121321
36347
Here is the script:
# cat sqrt
#!/bin/bash
if [ $# -ne 1 ]
then
echo 'Usage: sqrt number'
exit 1
else
echo -e "sqrt($1)\nquit\n" | bc -q -i
fi
# split, have a large file that you need to split into smaller chucks? A
mysqldump maybe? split is your command. Below I split a 250MB file into 2
megabyte chunks all starting with the prefix LF_.
# ls -lh largefile
-rw-r--r-- 1 root root 251M Feb 19 10:27 largefile
# split -b 2m largefile LF_
# ls -lh LF_* | head -n 5
-rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_aa
-rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ab
-rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ac
-rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ad
-rw-r--r-- 1 root root 2.0M Feb 19 10:29 LF_ae
# ls -lh LF_* | wc -l
126
# nl numbers lines. I had a script doing this for me for years until I found
out about nl.
# head wireless.h
/*
* This file define a set of standard wireless extensions
*
* Version : 20 17.2.06
*
* Authors : Jean Tourrilhes - HPL
* Copyright (c) 1997-2006 Jean Tourrilhes, All Rights Reserved.
*/
#ifndef _LINUX_WIRELESS_H
# nl wireless.h | head
1 /*
2 * This file define a set of standard wireless extensions
3 *
4 * Version : 20 17.2.06
5 *
6 * Authors : Jean Tourrilhes - HPL
7 * Copyright (c) 1997-2006 Jean Tourrilhes, All Rights Reserved.
8 */
9 #ifndef _LINUX_WIRELESS_H
# mkfifo is the coolest one. Sure you know how to create a pipeline piping
the output of grep to less or maybe even perl. But do you know how to make
two commands communicate through a named pipe?
First let me create the pipe and start writing to it:
mkfifo pipe; tail file > pipe
Then read from it:
cat pipe
# ldd, want to know which Linux thread library java is linked to?
# ldd /usr/java/jre1.5.0_11/bin/java
libpthread.so.0 => /lib/tls/libpthread.so.0 (0x00bd4000)
libdl.so.2 => /lib/libdl.so.2 (0x00b87000)
libc.so.6 => /lib/tls/libc.so.6 (0x00a5a000)
/lib/ld-linux.so.2 (0x00a3c000)
# col, want to save man pages as plain text?
# PAGER=cat
# man less | col -b > less.txt
# xmlwf, need to know if a XML document is well formed? (A configuration
file maybe..)
# curl -s 'http://bashcurescancer.com' > bcc.html
# xmlwf bcc.html
# perl -i -pe 's@<br/>@<br>@g' bcc.html
# xmlwf bcc.html
bcc.html:104:2: mismatched tag
# lsof lists open files. You can do all kinds of cool things with this. Like
find which ports are open:
# lsof | grep TCP
portmap 2587 rpc 4u IPv4 5544 TCP *:sunrpc
(LISTEN)
rpc.statd 2606 root 6u IPv4 5585 TCP *:668
(LISTEN)
sshd 2788 root 3u IPv6 5991 TCP *:ssh
(LISTEN)
sendmail 2843 root 4u IPv4 6160 TCP
badhd:smtp (LISTEN)
vsftpd 9337 root 3u IPv4 34949 TCP *:ftp
(LISTEN)
cupsd 16459 root 0u IPv4 41061 TCP
badhd:ipp (LISTEN)
sshd 16892 root 3u IPv6 61003 TCP
badhd.mshome.net:ssh->kontiki.mshome.net:4661 (ESTABLISHED)
Note: OpenBSD 101 pointed out that "lsof -i TCP" a better way to obtain this
same information. Thanks!
Or find the number of open files a user has. Very important for running big
applications like Oracle, DB2, or WebSphere:
# lsof | grep ' root ' | awk '{print $NF}' | sort | uniq | wc -l
--
Sharjeel
http://www.sharjeel.net
[Non-text portions of this message have been removed]
