Interesting Command Line Tips and Tricks in Linux

[root@linuxhelp ~]# HISTTIMEFORMAT=" %d/%m/%y %T " 
[root@linuxhelp ~]# history
    6  25/03/16 07:19:52 fdisk -l
    7  25/03/16 07:19:52 fdisk /dev/sdb
    8  25/03/16 07:19:52 fdisk -l
    9  25/03/16 07:19:52 fdisk -l /dev/sdb
   10  25/03/16 07:19:52 fdisk -l /dev/sda
   11  25/03/16 07:19:52 fdisk /dev/sda
   12  25/03/16 07:19:52 fdisk -l /dev/sda
   13  25/03/16 07:19:52 fdisk -s /dev/sda2
   14  25/03/16 07:19:52 fdisk -l /dev/sda
   15  25/03/16 07:19:52 fdisk /dev/sda
   16  25/03/16 07:19:52 cd
   17  25/03/16 07:19:52 vim /etc/sysconfig/network
   .  .  .   .  .
   .  .  .   .  .
   .  .  .   .  .
   990  25/03/16 03:30:35 dd if=/dev/zero of=/tmp/output.img bs=8k count=256k conv=fdatasync  rm -rf /tmp/output.img
  991  25/03/16 03:32:50 du -hsx * | sort -rh | head -6
  992  25/03/16 03:37:46 stat fedora.iso
  993  25/03/16 03:38:33 cd Desktop/
  994  25/03/16 03:40:14 stat Screenshot222.png
  995  25/03/16 03:40:32 pwd
  996  25/03/16 03:40:42 cd /home/jagannath/
  997  25/03/16 03:40:55 cd Desktop/
  998  25/03/16 03:40:58 pwd
  999  25/03/16 03:41:08 stat Screenshot222.png
 1000  25/03/16 03:44:23 man $(ls /bin | shuf | head -1)
 1001  25/03/16 07:19:55 cd
 1002  25/03/16 07:19:58 clear
 1003  25/03/16 07:20:13 history
 1004  25/03/16 07:22:59 HISTTIMEFORMAT=" %d/%m/%y %T " 
 1005  25/03/16 07:23:08 history

Add the below line to ~/.bashrc, If you need to append this change permanently.

[root@linuxhelp ~]# export HISTTIMEFORMAT=" %d/%m/%y %T " 
[root@linuxhelp ~]# source ~/.bashrc

Explanation of commands are,

History denotes as GNU History Library.
HISTIMEFORMAT is the Environmental Variable.
%d denotes as Day.
%m denotes as Month.
%y denotes as Year.
%T denotes the Time Stamp.
source represents in short send the contents of file to shell.
.bashrc denotes a shell script, if it started interactively then BASH start to run.

dd command

Using dd command, we can check disk write speed.

[root@linuxhelp ~]# dd if=/dev/zero of=/tmp/output.img bs=8k count=256k conv=fdatasync  rm -rf /tmp/output.img
262144+0 records in
262144+0 records out
2147483648 bytes (2.1 GB) copied, 20.7229 s, 104 MB/s

Explanation of commands are,
dd mentions Convert and Copy a file.
if=/dev/zero denotes Read the file and not stdin.
of=/tmp/output.img command used to Write to file and not stdout.
bs used to Read and Write maximum upto M bytes, at one time.
count used to Copy N input block.
conv is the command line used to Convert the file as per comma separated symbol list.
rm used to Removes files and folder.
-rf used to (-r) removes directories and contents recursively and (-f) Force the removal without prompt.

du command

Using du command, we can check first six files that occupying more space in your system.

[root@linuxhelp ~]# du -hsx * | sort -rh | head -6
287M    gitlab-7.7.1_omnibus.5.4.1.ci-1.el6.x86_64.rpm
11M    j
11M    home
4.4M    gitlab-workhorse
3.3M    mantisbt-1.2.19.zip
116K    install.log

Explanation of commands are,
du needs to Estimate file space usages.
-hsx used to (-h) Human Readable Format, (-s) Summaries Output, (-x) One File Format, skip directories on other file format.
sort command is used to Sort text file lines.
-rh used to (-r) Reverse the result of comparison, (-h) for compare human readable format.
head is the command used to output first n lines of file.

stat command

Using stat command, we can get the statistics related to a file.

stat filename_ext (viz., stat abc.pdf)

[root@linuxhelp ~]# cd /tmp
[root@linuxhelp tmp]# stat csf.tgz
File: `csf.tgz' 
Size: 688544 Blocks: 1352 IO Block: 4096 regular file
Device: 802h/2050d Inode: 693045 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2016-03-17 10:09:01.858006913 +0530
Modify: 2016-02-25 23:23:17.000000000 +0530
Change: 2016-03-17 09:59:49.626007416 +0530

[root@linuxhelp tmp]# stat autoinstaller3.log
File: `autoinstaller3.log' 
Size: 12020 Blocks: 24 IO Block: 4096 regular file
Device: 802h/2050d Inode: 656910 Links: 1
Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2016-03-19 07:45:51.854643390 +0530
Modify: 2016-03-19 08:35:23.938004452 +0530
Change: 2016-03-19 08:35:23.938004452 +0530

[root@linuxhelp tmp]# man $(ls /bin | shuf | head -1)
OSTNAME(1) Linux Programmer’ s Manual HOSTNAME(1)

NAME
hostname - show or set the system’ s host name
domainname - show or set the system’ s NIS/YP domain name
dnsdomainname - show the system’ s DNS domain name
nisdomainname - show or set system’ s NIS/YP domain name
ypdomainname - show or set the system’ s NIS/YP domain name

SYNOPSIS
hostname [-v] [-a] [--alias] [-d] [--domain] [-f] [--fqdn] [-A] [--all-
fqdns] [-i] [--ip-address] [-I] [--all-ip-addresses] [--long] [-s]
[--short] [-y] [--yp] [--nis]

hostname [-v] [-F filename] [--file filename] [hostname]

domainname [-v] [-F filename] [--file filename] [name]

nodename [-v] [-F filename] [--file filename] [name]

hostname [-v] [-h] [--help] [-V] [--version]

dnsdomainname [-v]
nisdomainname [-v]
ypdomainname [-v]

:q----> to quit