Bash: Let me bash that for you, Part 0

I was going to write about some Unix-like shell hints which I usually use like grep, sed, for loop, variables and so on. I noticed that I do usually use lots of bash kung-fu beyond the shadow of a doubt.

I'm not going to start a holly war what shell is the best one - sh, ksh or whatever. I know how to cook bash tasty - it has lots in common with sh but some nuances happen.

That isn't a bash tutorial or so - it's more like commonly used hints and tips.

man anycommand

Each man has to know unix command man. That's manual, dude.

pwd

prints path of working directory

$ pwd 
/home/user

ls path

list of directory

$ ls /tmp
myfile

Hint: . (dot) in unix-like systems is current directory

$ ls .
myfile

Hint: when path isn't specified ls uses current directory

$ ls 
myfile

Hint: option -l prints a long file format with ownership info, file size and so on

$ ls -l 
-rw-r--r-- 1 user user 12 Jul  7 11:00 myfile

Hint: option -h prints file size in human readable format - Kilobytes, Megabytes etc

$ ls -lh Java\ Concurrency\ In\ Practice.pdf 
-rw-r--r-- 1 user user 3.9M May 22  2009 Java Concurrency In Practice.pdf

cd path

change directory

$ cd /tmp 

• cd path/of/my/destination/
  Hint: I prefer use cd target/destitaton/path instead of several cd. It's much better, believe me. That's the benefit :
  
  • cd -
    return back to previous directory in the change directory history
    

    $ pwd 
    /tmp
    $ mkdir -p a/b/c/d/e
    $ cd a/b/c/d
    $ pwd
    /tmp/a/b/c/d
    $ cd -
    $ pwd
    /tmp

  • revert search over bash command history
    It's possible to search in already executed commands using bash.
    Ctrl + r typing
    For instance
    

    // Ctrl + r cd a
    $ cd a/b/c/d
    

• cd ~
  move to home directory
  

  $ cd ~
  $ pwd
  /home/user




• cd
  shortcut for cd ~
  

  $ cd
  $ pwd
  /home/user

chown options owner:group filename(s)

changes ownership of file(s). Every file in Unix has user ownership, group and other permissions.

$ ls -la myfile
-rw-r----- 1 user user 12 Jul  7 11:00 myfile
$ chown user2 myfile
$ ls -la myfile
-rw-r----- 1 user2 user 12 Jul  7 11:00 myfile

chmod options filename(s)

changes mode file(s). Every file (in general directory is file too) in Unix has three permissions:

• user (owner)
• group
• others

There are three types of permissions:

• read = 4
• write = 2
• execute = 1

Two ways how to change mode:

• numeric:
  1st digit corresponds to user permissions.
  2nd digit corresponds to group permissions.
  3rd digit corresponds to other permissions.
  
  Every digit is sum of permission type, e.g.
  read + write = 4 + 2 = 6
  read + write + execute = 4 + 2 + 1 = 7
  
  Note: When change mode it doesn't keep previous permissions - permission type = 6 means that it has read + write but no executable.
  
  Example:
  

  $ chmod 640 myfile
  $ ls -la myfile
  -rw-r----- 1 user user 12 Jul  7 11:00 myfile
  $ chmod 754 myfile
  $ ls -la myfile
  -rwxr-xr-- 1 user user 12 Jul  7 11:00 myfile
  

• symbolic
  Change permission in human readable way:
  u+r grants readable permission to user
  g-w removes writable permission from group
  
  Note: In this case chmod keeps previous permissions.

$ ls -la myfile
-rwxr-xr-- 1 user user 12 Jul  7 11:00 myfile
$ chmod o-r myfile
$ ls -la myfile
-rwxr-x--- 1 user user 12 Jul  7 11:00 myfile
$ chmod g+w myfile
$ ls -la myfile
-rwxrwx--- 1 user user 12 Jul  7 11:00 myfile

Background and foreground processes

• Hotkey Ctrl + z stops/resumes command execution
  

  $ gzip application.log 
  ^Z
  [1]+  Stopped                gzip application.log
  

  It means that we've got job #1 which is gzip application.log has state Stopped.
  
• jobs
  get the current bash session job list
  

  $ jobs
  [1]+  Stopped                gzip application.log

• fg job#
  move job job# to foreground
  

  $ fg 1
  gzip application.log

• bg job#
  move job job# to background
  

  $ bg 1
  [1]+ gzip application.log &
  $
  [1]+  Done                    gzip application.log

• command &
  move command execution to background
  

  $ gzip application.log &
  [1] 364
  $ jobs
  [1]+ Running                 gzip application.log
  $
  [1]+  Done                   gzip application.log

• wait pid
  wait while background processes with pid will be finished
  

  $ gzip application.log &
  [1] 415
  $ wait 415
  [1]+  Done                   gzip application.log

Hint: use simple wait to await to finish all background processes.

history number-of-items

prints last number-of-items (if specified or all otherwise) executed commands.

$ history 3
  558  ls
  559  cd ~/
  560  history 

Hint: to run n-th command in history use exclamation mark

$ !558
ls
file                              myfile

Hint: to run last command use double exclamation mark

$ !!
ls
file                              myfile

sleep seconds

sleep for a specified number of seconds

$ date ; sleep 5; date
Sat Jul  7 22:47:36 MSK 2012
Sat Jul  7 22:47:41 MSK 2012

Hot keys

Ctrl + a - move cursor to the beginning of the line
Ctrl + e - move cursor to the end of the line

Ctrl + u - delete from cursor position to the beginning of the line 
Ctrl + k - delete from cursor position to the end of the line 
Ctrl + w - delete from cursor position to the beginning of the word 


Ctrl + r - search in the history of executed commands

Ctrl + l - clear screen
Ctrl + d - shortcut for exit

Ctrl + z - stop/resume command background execution
Ctrl + c - cancel foreground command execution

Esc . (dot) - add last argument of last executed command

Now, let's go and conquer the world.