ehabaziz2001@gmail.com wrote:

>Till now I can not the difference between STDIN command and STDOUT
>command till now.

They're not commands, they're files.

>Is cat stdin ?

"cat" reads the file you specify on the command line and writes it to
STDOUT.

--
Tim Slattery
Slattery_T@bls.gov

On 2006-04-07, ehabaziz2001@gmail.com wrote:
> Till now I can not the difference between STDIN command and STDOUT
> command till now.
>
> Give me pls example .
>
> Is cat stdin ?
> Is ls stdout or stdin ?

They are not commands, they (along with stderr) are streams
connected to a process. When a program uses read (or fread or
whatever any particular language uses) it is, by default, reading
from stdin. When a program outputs something (e.g., with printf),
it is sent to stdout.

#! /bin/sh
read var ## read a line from stdin
printf "%s\n" "$var" ## print to stdout

By default, stdin is connected to a keyboard, and stdout and
stderr are sent to your screen.

On the command line, these may be redirected to a file or a pipe:

read line < /etc/passwd ## connect read's stdin to the file /etc/passwd
printf "%s\n" "$line" > $HOME/xxx ## send the line to the file $HOME/xxx

In this example, the stdout of printf is connect to a pipe; that
pipe is connected to the stdin of tr:

printf "%s\n" "$line" | tr ':' '\n'

--
Chris F.A. Johnson, author |
Shell Scripting Recipes: | My code in this post, if any,
A Problem-Solution Approach | is released under the
2005, Apress | GNU General Public Licence