Ten Linux commands you may not have used before!Great!

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Perhaps you haven't used the last ten Linux commands.Quite useful.

1)pgrep

There is a p before the P grep name, and we can guess that it's related to a process, and it's grep, of course, and it's a process-related grep command.However, this command is primarily used to list process ID s.For example:

$ pgrep -u hchen 
 
22441 
 
22444

This command is equivalent to:

ps -ef | egrep '^hchen' | awk '{print $2}'

2)pstree

This command lists processes in a tree format.As follows:

[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 
 
`-xinetd

3)bc

This command mainly does a mathematical operation with high precision.Such as square roots.Here's a script we wrote using the bc command (filename: sqrt)

#!/bin/bash 
 
if [ $ 
 
then 
 
echo 'Usage: sqrt number' 
 
exit 1 
 
else 
 
echo -e "sqrt($1)\nquit\n" | bc -q -i 
 
fi

So we can use this script to do square root operations like this:

[hchen@RHELSVR5]$ ./sqrt 36 
 
6 
 
[hchen@RHELSVR5]$ ./sqrt 2.0000 
 
1.4142 
 
[hchen@RHELSVR5]$ ./sqrt 10.0000 
 
3.1622

4)split

If you have a very large file and you want to split it into smaller files, this command does it.

[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_ai

File merging only requires a simple merge, such as:

[hchen@RHELSVR5]#  cat LF_* >largefile.tar.gz

5)nl

The nl command is similar to the cat command except that it has an up sign.As follows:

[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,

6)mkfifo

Anyone familiar with Unix should know that this is a system call or command that creates a named pipe.Usually, we string commands together on the command line with a vertical line'|'using a lifeless pipe.We use mkfifo with a well-known pipe.Here is an example:

Here's how to create a named pipe:

[hchen@RHELSVR5 ~]# mkfifo /tmp/hchenpipe 
 
[hchen@RHELSVR5 ~]# ls -l /tmp 
 
prw-rw-r-- 1 hchen hchen 0 05-10 18:58 hchenpipe

Then, we run the following command in a shell, which will not return unless someone reads away information from this well-known pipe.

[hchen@RHELSVR5 ~]# ls -al > /tmp/hchenpipe

We read the information in this pipeline in another command window: (it causes 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

7)ldd

This command lets you know that one of your executables uses a dynamic link library.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)

8)col

This command lets you turn a man file into a plain text file.Examples include the following:

# PAGER=cat 
 
# man less | col -b > less.txt

9)xmlwf

This command lets you check if an XML document has all tag s working.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 Speed 
 
100 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

You can list the 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)

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Publishing time: 2020-05-03
Author of this article: Chen Hao
This article comes from: Zero Degree of Career "To learn more about the" Zero Degree of Career"

Tags: Linux xml Apache ssh

Posted on Tue, 05 May 2020 12:23:23 -0400 by nielst