how does exec() do it? on successful call of exec() family of functions, they never return...
how to i emulate that.
assume the standard example,
now this would never return.
i m trying to emulate exec()'s never to return feature...
i m not trying anything fancy...only to emulate the "no return" feature once a command is executed.
so when i run this program
(trial 1)
(trial 2)
i get what i want...the line "this should never be executed" never gets printed
please help me grasp the internals of exec() call... and explain to me how it works
also please explain to me, why in execl*() a set of arguments is preferred to be passed as in
when it could have been implemented as
instead
i have same complaint with execv*() style exec()...
By calling exit within a function as you have done and there is no need for sleeping. My take on why execl ("/bin/ls", "ls -l", (char *)0) is not implemented that way is maybe it is best to separate the command from its options and arguments to make it more flexible.
The arguments absolutely must be separated because each argument will be a separate element in the argv array. Things like shells and the system() subroutine accept arguments separated by spaces, but they must isolate each argument prior to calling exec().
exec() tells the kernel to replace the current existing program with a new program. The kernel roughly:
1. saves a copy of the new argv array and a copy of the environment
2. frees any private memory area
3. disconnects the process from any shared memory area including a shared text segment and any shared libraries.
Note: At this point, any code following the exec call no longer exists in the process. The same is true of any code prior to the exec call and even the exec call itself. It's all gone.
4. reads in the exec'ed program and reconstructs a working program. The environment and the arguments are copied into the new program.
5. transfers control to the newly created program.
Note that this all happens in one process. The process id does not change. The program that the process is running changes. After an exec() a process might be smaller (use less memory) than it did prior to the exec().
You can't emulate stuff like this in userland. Only the kernel can do this sort of thing.
Hi,
I am studying exec family of functions.Its man page says,it replaces the current process image with a new process image. If it replaces the binary,then after returning back,how does it get the previous parameters of the process which called exec?As replacing process image means replacing... (5 Replies)
Hi,
I am studying exec family of functions.Its man page says,it replaces the current process image with a new process image. If it replaces the binary,then after returning back,how does it get the previous parameters of the process which called exec?As replacing process image means replacing all... (1 Reply)
Hi
i am in learning phase of unix.
i was going through exec in a unix book. below is the command
exec n>file
exec n>>file
however when i used the exec command like below , where ex is the file name
exec 2>>exand then do ls -lrt then again when i do the ls -lrt to see the size of the file... (3 Replies)
I have the following bash script lines in a file named test.sh.
#!/bin/bash
#
# Write Date to cron.log
#
echo "Begin SSI Load $(date +%d%b%y_%T)"
#
# Get the latest rates file for processing.
#
d=$(ls -tr /rms/data/ssi | grep -v "processed" | tail -n 1)
filename=$d
export filename... (3 Replies)
hello
is there a family tree, or words that would illustrate the family tree of,
Unix -> Linux
As i would understand Unix, it is a OS.
And Linux is a ?, is Linux a OS or a sub structure inside of the Unix OS ?.
Have you ever seen one of those family tree`s where ma and pa are shown at... (3 Replies)
Hi, experts.
Whould anybody clear explay me difference and usage of these 3 commands (particulary in bash) :
exec
eval
source
I've tryed to read the manual pages but did not get much.
Also could not get something useful from Google search - just so much and so not exactly, that is... (3 Replies)
Hi,
I compiled with no error a C program, than I tryed to execute it and than I get this error:
connessione al server fallita: Address family not supported by protocol family
What does it mean?
Why I get this error only on Mac os x while on Ubuntu the program works?
The code is:... (3 Replies)
Is there any facility to filter/identify the data calls and voice calls coming throug modem?
OR
Can we get the data or voice calls information through a script(preferably C Kermit)? (0 Replies)