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Communication between processes in Unix

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Top Forums Shell Programming and Scripting Communication between processes in Unix
# 1  
Old 12-23-2009
Bug Communication between processes in Unix
hi folks!!
I was stuck with a little problem where i needed to communcate between two processes, i.e., send a command to the parent process from the child process as soon as the child process terminates.This was required when i wanted to create a log using the script command in a bourne shell.The following is the script that i am running:
Code:
#!/bin/sh
set -x
echo `date`|sed "s/[:' ']//g" >name
 head -1  name | read name1
script ./logs/$name1.txt
if [ $0=exit ];
then
exit
logout #*#
fi

~
#*# At this point in the code, when the user wants to exit, i need to ask the parent process to logout (send the logout command in the process) so that the user finally gets out of the server.


Can anyone help me in this?
Last edited by pludi; 12-23-2009 at 07:52 AM.. Reason: code tags, please...
# 2  
Old 12-23-2009
Quote:
Originally Posted by bdiwakarteja
hi folks!!
I was stuck with a little problem where i needed to communcate between two processes, i.e., send a command to the parent process from the child process as soon as the child process terminates.

A child process cannot affect its parent.

The parent must use the output or exit status of the child.
Quote:
This was required when i wanted to create a log using the script command in a bourne shell.The following is the script that i am running:
Code:
#!/bin/sh
set -x
echo `date`|sed "s/[:' ']//g" >name


Why echo?

Why sed?

Why not use a format string with date?
Quote:
Code:
 head -1  name | read name1


Why use head? (And the name1 variable will not be available anywhere else in the script unless you are using ksh)

Code:
read name1 < name

But why are you using a temporary file?
Quote:
Code:
script ./logs/$name1.txt
if [ $0=exit ];


That will always be true (or a syntax error if $0 contains spaces).

Why would you expect $0 to contain exit? $0 contains the path to the current script.
Quote:
Code:
then
exit
logout #*#
fi

~
#*# At this point in the code, when the user wants to exit, i need to ask the parent process to logout (send the logout command in the process) so that the user finally gets out of the server.


Can anyone help me in this?
# 3  
Old 12-23-2009
Bug communication
hi.. I am sorry for confusing you on this.Trust me, i am just a beginner in shell scripting. I was merely trying to create a file containing all the commands and the outputs that the user tries on the shell and save it with the filename of the output of the date command modified with the sed command. Thats why i used sed command to create the filename and $name1 will contain the output of the date command after filtered.
But finally made a mistake in the $0 line of the command as u rightly pointed out.

But, is there a way that we can send a number as an exit status to the parent process and the latter then determines the next action to be carried out.If yes, whats the command?

Thanks in advance.
Last edited by bdiwakarteja; 12-23-2009 at 02:36 PM.. Reason: corrections
# 4  
Old 12-23-2009
Quote:
Originally Posted by bdiwakarteja
hi.. I am sorry for confusing you on this.Trust me, i am just a beginner in shell scripting. I was merely trying to create a file containing all the commands and the outputs that the user tries on the shell and save it with the filename of the output of the date command modified with the sed command. Thats why i used sed command to create the filename and $name1 will contain the output of the date command after filtered.

There is no need to use sed. You can use a format string as an argument to date:

Code:
filename=$(date +%Y-%m-%d.txt)

Quote:
But finally made a mistake in the $0 line of the command as u rightly pointed out.

But, is there a way that we can send a number as an exit status to the parent process and the latter then determines the next action to be carried out.If yes, whats the command?

Normally, the exit status of a command is contained in the special parameter, $?, but script always seems to exit without an error.
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