Linux is the most suitable operating system for development. It gives all operational power to the user, and whatever operations are performed will reflect in the system’s structure. Openness, freedom, and honesty are its greatest charms.
01 pgrep
The ‘p’ in pgrep hints that it is related to processes, and since it includes ‘grep’, this command is indeed related to listing process IDs. For example:
$ pgrep -u hchen2244122444This command is equivalent to:
ps -ef | egrep '^hchen' | awk '{print $2}'02 pstree
This command can list processes in a tree format. As shown below:
[hchen@RHELSVR5 ~]$ pstree
init-+-acpid
|-auditd-+-python
| `-{auditd}
|-automount---4*[{automount}]
|-backup.sh---sleep
|-dbus-daemon
|-events/0
|-events/1
|-hald---hald-runner---hald-addon-acpi
|-httpd---10*[httpd]
|-irqbalance
|-khelper
|-klogd
|-ksoftirqd/0
|-ksoftirqd/1
|-kthread-+-aio/0
| |-aio/1
| |-ata/0
| |-ata/1
| |-ata_aux
| |-cqueue/0
| |-cqueue/1
| |-kacpid
| |-kauditd
| |-kblockd/0
| |-kblockd/1
| |-kedac
| |-khubd
| |-6*[kjournald]
| |-kmirrord
| |-kpsmoused
| |-kseriod
| |-kswapd0
| |-2*[pdflush]
| |-scsi_eh_0
| |-scsi_eh_1
| |-xenbus
| `-xenwatch
|-migration/0
|-migration/1
|-6*[mingetty]
|-3*[multilog]
|-mysqld_safe---mysqld---9*[{mysqld}]
|-smartd
|-sshd---sshd---sshd---bash---pstree
|-svscanboot---svscan-+-3*[supervise---run]
| |-supervise---qmail-send-+-qmail-clean
| | |-qmail-lspawn
| | `-qmail-rspawn
| `-2*[supervise---tcpserver]
|-syslogd
|-udevd
|-watchdog/0
|-watchdog/1
-xinetd03 bc
This command is mainly used for high-precision mathematical calculations, such as calculating square roots. Below is a script we wrote using the bc command (filename: sqrt)
#!/bin/bash
if [ $# -ne 1 ]
then echo 'Usage: sqrt number'
exit 1
else echo -e "sqrt($1)\nquit\n" | bc -q -fi
Thus, we can use this script to perform square root calculations:
[hchen@RHELSVR5]$ ./sqrt 366
[hchen@RHELSVR5]$ ./sqrt 2.0000
1.4142
[hchen@RHELSVR5]$ ./sqrt 10.0000
3.1622
04 split
[hchen@RHELSVR5 applebak]# ls -l largefile.tar.gz
-rw-r--r-- 1 hchen hchen 436774774 04-17 02:00 largefile.tar.gz
[hchen@RHELSVR5 applebak]# split -b 50m largefile.tar.gz LF_
[hchen@RHELSVR5]# ls -l LF_*
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:34 LF_aa
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:34 LF_ab
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:34 LF_ac
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:34 LF_ad
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:34 LF_ae
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:35 LF_af
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:35 LF_ag
-rw-r--r-- 1 hchen hchen 52428800 05-10 18:35 LF_ah
-rw-r--r-- 1 hchen hchen 17344374 05-10 18:35 LF_aiTo merge the files back, simply use the following command:[hchen@RHELSVR5]# cat LF_* >largefile.tar.gz05 nl
<span>nl</span> command is similar to the <span>cat</span> command, except it adds line numbers. As shown below:
[hchen@RHELSVR5 include]# nl stdio.h | head -n 10 1 /* Define ISO C stdio on top of C++ iostreams. 2 Copyright (C) 1991,1994-2004,2005,2006 Free Software Foundation, Inc. 3 This file is part of the GNU C Library. 4 The GNU C Library is free software; you can redistribute it and/or 5 modify it under the terms of the GNU Lesser General Public 6 License as published by the Free Software Foundation; either 7 version 2.1 of the License, or (at your option) any later version. 8 The GNU C Library is distributed in the hope that it will be useful,
06 mkfifo
[hchen@RHELSVR5 ~]# mkfifo /tmp/hchenpipe
[hchen@RHELSVR5 ~]# ls -l /tmp
prw-rw-r-- 1 hchen hchen 0 05-10 18:58 hchenpipe
[hchen@RHELSVR5 ~]# ls -al > /tmp/hchenpipeIn another command window, we read the information from this pipe (which will cause the previous command to return):
[hchen@RHELSVR5 ~]# head /tmp/hchenpipe
drwx------ 8 hchen hchen 4096 05-10 18:27 .
drwxr-xr-x 7 root root 4096 03-05 00:06 ..
drwxr-xr-x 3 hchen hchen 4096 03-01 18:13 backup
-rw------- 1 hchen hchen 721 05-05 22:12 .bash_history
-rw-r--r-- 1 hchen hchen 24 02-28 22:20 .bash_logout
-rw-r--r-- 1 hchen hchen 176 02-28 22:20 .bash_profile
-rw-r--r-- 1 hchen hchen 124 02-28 22:20 .bashrc
-rw-r--r-- 1 root root 14002 03-07 00:29 index.htm
-rw-r--r-- 1 hchen hchen 31465 03-01 23:48 index.php
07 ldd
This command can show you the dynamic link libraries used by an executable file. For example:
[hchen@RHELSVR5 ~]# ldd /usr/bin/java linux-gate.so.1 => (0x00cd9000) libgij.so.7rh => /usr/lib/libgij.so.7rh (0x00ed3000) libgcj.so.7rh => /usr/lib/libgcj.so.7rh (0x00ed6000) libpthread.so.0 => /lib/i686/nosegneg/libpthread.so.0 (0x00110000) librt.so.1 => /lib/i686/nosegneg/librt.so.1 (0x009c8000) libdl.so.2 => /lib/libdl.so.2 (0x008b5000) libz.so.1 => /usr/lib/libz.so.1 (0x00bee000) libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00aa7000) libc.so.6 => /lib/i686/nosegneg/libc.so.6 (0x0022f000) libm.so.6 => /lib/i686/nosegneg/libm.so.6 (0x00127000) /lib/ld-linux.so.2 (0x00214000)
08 col
This command can convert man files into plain text files. As shown in the example below:
# PAGER=cat
# man less | col -b > less.txt
09 xmlwf
This command can check if an XML document has all tags properly formatted. For example:
[hchen@RHELSVR5 ~]# curl 'https://coolshell.cn/?feed=rss2' > cocre.xml % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed100 64882 0 64882 0 0 86455 0 --:--:-- --:--:-- --:--:-- 2073k
[hchen@RHELSVR5 ~]# xmlwf cocre.xml
[hchen@RHELSVR5 ~]# perl -i -pe 's@<link>@<br>@g' cocre.xml
[hchen@RHELSVR5 ~]# xmlwf cocre.xml
cocre.xml:13:23: mismatched tag
10 lsof
This command can list open files.
[root@RHELSVR5 ~]# lsof | grep TCP
httpd 548 apache 4u IPv6 14300967 TCP *:http (LISTEN)
httpd 548 apache 6u IPv6 14300972 TCP *:https (LISTEN)
httpd 561 apache 4u IPv6 14300967 TCP *:http (LISTEN)
httpd 561 apache 6u IPv6 14300972 TCP *:https (LISTEN)
sshd 1764 root 3u IPv6 4993 TCP *:ssh (LISTEN)
tcpserver 8965 root 3u IPv4 153795500 TCP *:pop3 (LISTEN)
mysqld 10202 mysql 10u IPv4 73819697 TCP *:mysql (LISTEN)
sshd 10735 root 3u IPv6 160731956 TCP 210.51.0.232:ssh->123.117.239.68:31810 (ESTABLISHED)
sshd 10767 hchen 3u IPv6 160731956 TCP 210.51.0.232:ssh->123.117.239.68:31810 (ESTABLISHED)
vsftpd 11095 root 3u IPv4 152157957 TCP *:ftp (LISTEN)
THE END—
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