Standard I/P and Standard O/P

Redirecting I/P and O/P

Pipes

Standard I/P and Standard O/P

Most Unix system commands take input from your terminal and send the resulting output back to your terminal. A command normally reads its input from a place called standard input, which happens to be your terminal by default. Similarly, a command normally writes its output to standard output, which is also your terminal by default.
• I/P from standard input i.e. terminal and O/P to standard O/P i,e, terminal
  [shell_test@localhost ~]$ ls -l
  total 32
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Desktop
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Documents
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Download
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Music
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Pictures
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Public
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Templates
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Videos
  [shell_test@localhost ~]$

Redirecting I/P and O/P

• Redirecting O/P to a file i.e. other than terminal

  1. Using ‘>’

  [shell_test@localhost ~]$ ls -l > listoffiles
  [shell_test@localhost ~]$ cat listoffiles
  total 32
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Desktop
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Documents
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Download
  -rw-rw-r–. 1 shell_test shell_test 0 2009-11-14 14:35 listoffiles
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Music
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Pictures
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Public
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Templates
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Videos
  [shell_test@localhost ~]$

  2. Append more results using ‘>>’

  [shell_test@localhost ~]$ ls >> listoffiles
  [shell_test@localhost ~]$ cat listoffiles
  total 32
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Desktop
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Documents
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Download
  -rw-rw-r–. 1 shell_test shell_test 0 2009-11-14 14:35 listoffiles
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Music
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Pictures
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Public
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Templates
  drwxr-xr-x. 2 shell_test shell_test 4096 2009-11-09 06:29 Videos
  Desktop
  Documents
  Download
  listoffiles
  Music
  Pictures
  Public
  Templates
  Videos
  [shell_test@localhost ~]$

• Getting I/P from files

  1. use ‘<'

  [shell_test@localhost ~]$ wc -l listoffiles
  19 listoffiles
  [shell_test@localhost ~]$

Pipes

• Pipes are used to redirect O/P of one command to I/P of other command
  see following example
  1. [shell_test@localhost tmp]$ who > users
     [shell_test@localhost tmp]$ cat users
     gpvprasad tty1 2009-11-18 21:38 (:0)
     gpvprasad pts/0 2009-11-18 22:06 (:0.0)
     [shell_test@localhost tmp]$ wc -l users
     2 users
     [shell_test@localhost tmp]$

  which can be executed in single line using ‘|’

  1. [shell_test@localhost tmp]$ who | wc -l
     2
     [shell_test@localhost tmp]$

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