20 Useful Linux command-line tricks

Unix Command Line Tricks–part I

http://www.cyberciti.biz/open-source/command-line-hacks/20-unix-command-line-tricks-part-i/

Deleting a HUGE file

I had a huge log file 200GB I need to delete on a production Web server. My rm and LS command was crashed and I were afraid the system to a crawl with huge disk I/O load. To remove a HUGE file, enter:

>/path/to/file.log# or use the following syntax: >/path/to/file.log # finally delete it Rm/path/to/file.log

Want to cache console output?

Try the script command line utility to create a typescript of everything printed on your terminal.

Script My.terminal.sessio

Type commands:

Lsdatesudo Service Foo Stop

To exit (to end script session) type exit or logout or presscontrol-D

Exit

To view type:

More my.terminal.sessionless My.terminal.sessioncat my.terminal.session

Restoring deleted/tmp Folder

As my journey continues with Linux and Unix shell, I made a few mistakes. I accidentally deleted/tmp folder. To restore it all you have to do is:

Mkdir/tmpchmod 1777/tmpchown root:root/tmpls-ld/tmp

Locking a Directory

For privacy the My data I wanted to lock down/downloads on my file server. So I ran:

chmod 0000/downloads

The root user can still has access and LS and CD commands won't work. To go back:

chmod 0755/downloads

Password protecting file in vim text editor

Afraid that root user or someone could snoop into your personal text files? Try password protection to a file in Vim, type:

Vim +x filename

Or, before quitting in vim with vim :X command to encrypt your file and Vim would prompt for a password.

Clear gibberish all over the screen

Just Type:

Reset

Becoming human

Pass the -h or other -H options command line option to GNU or BSD utilities to get output of command commands Like LS, DF, Du, in human-understandable formats:

ls-lh# print sizes in human readable format (e.g., 1K 234M 2G) df-hdf-k# show output in bytes, KB, MB, or Gbfree-bfree -kfree-mfree-g# print sizes in human readable format (e.g., 1K 234M 2G) du-h# get file system perms in human readable fo Rmatstat-c%a/boot# Compare Human readable numberssort-h-a file# display the CPU information in human readable format On a linuxlscpulscpu-elscpu-e=cpu,node# Show the size of each file but in  a more human readable waytree-htree-h/b Oot

Show information about known users in the Linux based system

Just Type:

# # Linux version # #lslogins # # BSD version # #logins

Sample outputs:

UID USER pwd-lock Pwd-deny last-login GECOS 0 root 0 0 22:37:59 root 1 Bin 0               1 Bin 2 Daemon 0 1 Daemon 3 ADM 0 1 ADM 4 LP 0 1 LP 5 sync 0 1 Sync 6 shutdown 0 1 2014-d             EC17 shutdown 7 Halt 0 1 halt 8 mail 0 1 Mail ten UUCP            0 1 UUCP operator 0 1 operator Games 0 1            Games Gopher 0 1 Gopher FTP 0 1 ftp User mysql  0 1 MySQL Server # NTP 0 1 + Apache 0 1 Apache Haldaemon 0 1 HAL daemon VCSA 0 1 Virtual Console memory own ER tcpdump 0        1. sshd 0 1 privilege-separated SSH dbus 0 1 Syst        EM message bus postfix 0 1 Nobody 0 1 Nobody173 abrt 0          1497 Vnstat 0 1 Vnstat user498 nginx 0 1 nginx user499 saslauth 0 1 "SASLAUTHD user"

How does I fix mess created by accidentally untarred files on the current dir?

So I accidentally untar a tarball in/var/www/html/directory instead of/home/projects/www/current. It created mess in/var/www/html/. The easiest-to-fix this mess:

Cd/var/www/html//bin/rm-f "$ (tar ztf/path/to/file.tar.gz)"

Confused on a top command output?

Seriously, you need-try out htop instead of top:

sudo htop

Want to run the same command again?

Just type !! . For example:

/myhome/dir/script/name arg1 Arg2 # to run the same command again!! # to run, the last command again as root Usersudo!!

The !! repeats the most recent command. To run the most recent command beginning with "foo":

!foo# Run The most recent command beginning with "service" as Rootsudo!service

The use to run command with the last argument of the most !$ recent command:

# Edit Nginx.confsudo vi/etc/nginx/nginx.conf # Test nginx.conf for errors/sbin/nginx-t-c/etc/nginx/nginx.conf # after Testing a file with "/sbin/nginx-t-c/etc/nginx/nginx.conf", you# can edit file again with Visudo VI!$

Get a reminder if you had to leave

If you need a reminder to leave your terminal, type the following command:

Leave +HHMM

Where,

• hhmm-The time of day was in the form hhmm where HH was a time in hours (on a or hour clock), and mm are minutes. All times is converted to a hour clock, and assumed to is in the next hours.

Home Sweet Home

Want to go the directory is were just in? Run:
cd -
Need to quickly return to your home directory? Enter:
cd
The variable CDPATH defines the search path for the directory containing directories:

Export CDPATH=/VAR/WWW:/NAS10

Now, instead of typing cd /var/www/html/ I can simply type the following to CD into/var/www/html path:

CD HTML

Editing a file being viewed with less pager

To-edit a file being viewed with less pager, press v . You'll have the file for edit under $EDITOR:

Less *.cless foo.html## Press V to edit file # # # Quit from editor and you would return to the less pager again # #

List all files or directories on your system

To see all of the directories on your system, run:

Find/-type D | Less # List all directories in your $HOMEfind $HOME-type d-ls | Less

To see all of the files, run:

Find/-type F | Less # List All files in your $HOMEfind $HOME-type f-ls | Less

Build directory trees in a single command

You can create directory trees one at a time using mkdir command by passing the -p option:

Mkdir-p/jail/{dev,bin,sbin,etc,usr,lib,lib64}ls-l/jail/

Copy file into multiple directories

Instead of running:

Cp/path/to/file/usr/dir1cp/path/to/file/var/dir2cp/path/to/file/nas/dir3

Run the following command to copy file into multiple dirs:

Echo/usr/dir1/var/dir2/nas/dir3 |  Xargs-n 1 cp-v/path/to/file

Creating a Shell function is left as an exercise for the reader

Quickly find differences between, directories

The diff command compare files on line. It can also compare-directories:

Ls-l/tmp/rls-l/tmp/s# Compare-Folders using diff # #diff/tmp/r//tmp/s/

Fig.: Finding differences between folders

Text formatting

You can reformat each paragraph with fmt command. In this example, I ' m going to reformat file by wrapping overlong lines and filling short lines:

FMT file.txt

You can also split long lines, but does not refill i.e. wrap overlong lines, but does not fill short lines:

Fmt-s file.txt

See the output and write it to a file

Use the tee command as follows to see the output of the also write to a log file named My.Log:

Mycoolapp arg1 arg2 Input.file | Tee My.Log

The tee command ensures that you'll see Mycoolapp output on the screen and to a file same time.

20 Useful Linux command-line tricks