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Processes and exit status

 
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# 1  
Old 07-07-2011
Processes and exit status
Hi, I can't understand why the last $? is 1? can somebody plz help me to understand it? thanks
Code:
$ ksh
$ ps -f
     UID   PID  PPID  C    STIME TTY       TIME COMMAND
msarabad 12361 12319  0 15:17:58 pts/1     0:00 ksh
msarabad 12319 12317  0 15:15:11 pts/1     0:00 -sh
msarabad 12362 12361  0 15:18:04 pts/1     0:00 ps -f
$ exit
$ print $?
0
$ ksh
$ ps -f
     UID   PID  PPID  C    STIME TTY       TIME COMMAND
msarabad 12363 12319  0 15:18:16 pts/1     0:00 ksh
msarabad 12319 12317  0 15:15:11 pts/1     0:00 -sh
msarabad 12364 12363  0 15:18:19 pts/1     0:00 ps -f
$ exit 1
$ print $?
1
$

# 2  
Old 07-07-2011
By POSIX standards for the shell

exit returns 0 to the caller

exit n returns n to the caller where n is from 0 to 255.
# 3  
Old 07-07-2011
Ok, I got it up to this point. it means that even exit 89 will tell me 89. but why do we need to do this? how is it related to the fork processes? I got this exercise while I'm doing the exercises in shell POSIX tutorial in child/parent part.
# 4  
Old 07-07-2011
The idea is for you as a programmer to have a way of knowing when running your program how it ended (0 being its OK...) the program can very well be a shell script...
Lets say in your script you have a if condition where in one case you do not want the process to continue, you would give an exit value...
If you had multiple conditions, you would be pleased to know where you got out...
# 5  
Old 07-07-2011
thanks I got it. correct me..

the below example when I say exit, it will exit and the status is 0 but when I say exit 1 it also exits and the status is 1, so its a small sample of what you just said right? because all the processes before the exit are same! it is just showing that exit can have different numbers (0 - 255) ? am I right?
# 6  
Old 07-07-2011
Because a the termination status is NOT the same thing as exit which is a command here...
print $? will print the status of last command/program etc...
If you have placed in your instructions some exits, you can find out where you came out of your program because executing the exit will end the program! the return code will tell you why...
# 7  
Old 07-07-2011
Yes, don't just exit 1 at every error condition. Exit with a unique number for each possible error so you (or another script) can query the return code to see why it failed.

Make sure to comment that at the top:
Code:
##  Returns: 0-Success
##           1-Invalid number of args
##           2-File not found

 
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