I see a lot of errors in your code. I do not believe that it works. In fact when I look at code like this...
Quote:
Originally posted by badshah
if (strcmp(argv[0], "&")==0))
if ( (pid = fork() < 0 )
}while(strcmp(name,"exit));
I don't even believe that it will compile at all.
In general terms, you are on the right track. If we assume a shell without job control, "background" just means that we do not wait for the child.
A few comments...look at your line
if ( (pid = fork() < 0 )
The parentheses do not match up. It is critical that the test is done right. It should be
if ( (pid = fork()) < 0 )
When a system call fails, it will return a -1. I prefer explicitly testing for that. This is how you handled the execvp() system call. Also when a system call fails, it sets errno to an error code. If you display this value, it can help in debugging. And there is a sys_errlist that can decode errno. I like to do that as well. Also errors should go to stderr, not stdout. And exit codes should indicate whether or not the program worked. Put all of that together and this is how I would do it...
Now to use errno and sys_errlist. you are supposed to include errno.h. But sometimes another include picks them up.
There is no need to waitpid in a loop. Just wait for the process once.
And it looks like you are reading a command once, and then looping on it forever. You need to read a new command inside your loop.
Hello all,
How do I start a background process and save the process id to a file on my system. For example %wait 5 & will execute and print the process id. I can't figure out how to get it to a file. I've tried: > filename 0>filename 1>filename.
Any assistance is most appreciated.
Thanks,
Jim... (10 Replies)
Hi Guys,
I am facing some weird problem with my shell script. The script shows up a menu and for every ontion internally calls a shell script which start/stop various servers. When I am using '&' while calling the internal shell script so that the server run in the background. For exiting... (1 Reply)
Hi,
In shell script when I use
script1 >> filelog
the echo statments of script1 gets printed in the filelog
but when I try to run script in background i.e,
script1 & >> filelog
nothing gets printed in the filelog.
Anybody knows whats going on here.
thanks (3 Replies)
Hi,
I have a main script(main.ksh) within which I have called another script(sub.ksh). The sub.ksh script is made to run in the background using '&'. The main.ksh script logs the information in a logfile main_ddmmyy and the sub.ksh script also logs the information in the log file sub_ddmmyy.... (5 Replies)
I need to submit a script that will continue to run after logging out and after a reboot or shutdown.
I entered the following: nohup script &
The script continues to run in the background after logging off the system but is killed after a reboot or shutdown. Any help would be greatly... (1 Reply)
What I need to learn is how to use a script that launches background processes, and then kills those processes as needed.
The script successfully launches the script. But how do I check to see if the job exists before I kill it?
I know my problem is mostly failure to understand parameter... (4 Replies)
Hi,
I am using net::ftp for transferring files now i am trying in the same Linux server as a result ftp is very fast but if the server is other location (remote) then the file transferred will be time consuming.
So i want try putting FTP part as a background process. I am unaware how to do... (5 Replies)
Hi,
I have written a menu driven shell script in which as per the choice, I run the another script on background.
For eg:
1. get info
2)process info
3)modify info
All the operations have different scripts which i schedule in background using &.
However I wish to display the error... (0 Replies)
Discussion started by: ashima jain
0 Replies
LEARN ABOUT PHP
wait
wait(1) User Commands wait(1)NAME
wait - await process completion
SYNOPSIS
/bin/sh
wait [pid...]
/bin/jsh /bin/ksh /usr/xpg4/bin/sh
wait [pid...]
wait [ % jobid...]
/bin/csh
wait
DESCRIPTION
The shell itself executes wait, without creating a new process. If you get the error message cannot fork,too many processes, try using the
wait command to clean up your background processes. If this doesn't help, the system process table is probably full or you have too many
active foreground processes. There is a limit to the number of process IDs associated with your login, and to the number the system can
keep track of.
Not all the processes of a pipeline with three or more stages are children of the shell, and thus cannot be waited for.
/bin/sh, /bin/jsh
Wait for your background process whose process ID is pid and report its termination status. If pid is omitted, all your shell's currently
active background processes are waited for and the return code will be 0. The wait utility accepts a job identifier, when Job Control is
enabled (jsh), and the argument, jobid, is preceded by a percent sign (%).
If pid is not an active process ID, the wait utility will return immediately and the return code will be 0.
csh
Wait for your background processes.
ksh
When an asynchronous list is started by the shell, the process ID of the last command in each element of the asynchronous list becomes
known in the current shell execution environment.
If the wait utility is invoked with no operands, it will wait until all process IDs known to the invoking shell have terminated and exit
with an exit status of 0.
If one or more pid or jobid operands are specified that represent known process IDs (or jobids), the wait utility will wait until all of
them have terminated. If one or more pid or jobid operands are specified that represent unknown process IDs (or jobids), wait will treat
them as if they were known process IDs (or jobids) that exited with exit status 127. The exit status returned by the wait utility will be
the exit status of the process requested by the last pid or jobid operand.
The known process IDs are applicable only for invocations of wait in the current shell execution environment.
OPERANDS
The following operands are supported:
One of the following:
pid The unsigned decimal integer process ID of a command, for which the utility is to wait for the termination.
jobid A job control job ID that identifies a background process group to be waited for. The job control job ID notation is applicable
only for invocations of wait in the current shell execution environment, and only on systems supporting the job control option.
USAGE
On most implementations, wait is a shell built-in. If it is called in a subshell or separate utility execution environment, such as one of
the following,
(wait)
nohup wait ...
find . -exec wait ... ;
it will return immediately because there will be no known process IDs to wait for in those environments.
EXAMPLES
Example 1: Using A Script To Identify The Termination Signal
Although the exact value used when a process is terminated by a signal is unspecified, if it is known that a signal terminated a process, a
script can still reliably figure out which signal is using kill, as shown by the following (/bin/ksh and /usr/xpg4/bin/sh):
sleep 1000&
pid=$!
kill -kill $pid
wait $pid
echo $pid was terminated by a SIG$(kill -l $(($?-128))) signal.
Example 2: Returning The Exit Status Of A Process
If the following sequence of commands is run in less than 31 seconds (/bin/ksh and /usr/xpg4/bin/sh):
sleep 257 | sleep 31 &
jobs -l %%
then either of the following commands will return the exit status of the second sleep in the pipeline:
wait <pid of sleep 31>
wait %%
ENVIRONMENT VARIABLES
See environ(5) for descriptions of the following environment variables that affect the execution of wait: LANG, LC_ALL, LC_CTYPE, LC_MES-
SAGES, and NLSPATH.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), jobs(1), ksh(1), sh(1), attributes(5), environ(5), standards(5)SunOS 5.10 12 Dec 1997 wait(1)