Hi,
in my program i need to run an external program in background.I am aware that there are at least 2 alternatives for this:
1)fork+exec
2)system("program &");
I have read several posts about this,and they all tend to suggest to use fork+exec (and that's what i am doing now).
I have some questions though:
a) I read somewhere that "system" actually uses fork+exec (and the man page for "system" implicitly seems to confirm it).Can you confirm this?
b)in the original source code i started working on,the external program was run like this:
I don't think that's correct for ay least 2 reasons:
a)it doesn't check WIFEXITED before checking WEXITSTATUS
b)since i am interested in the exit value of the external program,i think that this code is wrong since it wil output only the "system" exit code,and not the external program's one(consider that the external program will run for a while,so its exit code will be outputted much later).
Am i correct?
This code is in my 'case' statement and it all else works fine.
The problem I have is that the value in 'procno' is not passed on to the external program (fireit).
It is passing all zeros instead of the actual process number.
By the time I get to this case statement, I know the "Number" and... (1 Reply)
Hello
I am getting error when the file (Folder or Application) path having space is given as external input to the shell program.
It works fine for the files which has no spaces in the file name
Thans, (5 Replies)
Hello,
in the application i'm writing i need to launch "recordmydesktop" to capture the screen,but i'm having a problem: when the recording stops,and the encoding of the saved file starts,the entire system hangs until the completion of the encoding.This happens if i launch recordmydesktop from my... (7 Replies)
Hi,
I have a query about processing and running Perl program at the background.
I have HTML file called Userform.html which accepts input from the user. As soon as input is given the contol goes to get.cgi (get.cgi does some processing and computing tasks).
Actually get .cgi takes more... (0 Replies)
Hello! I am currently attempting to build a very, very, basic program that attempts to act like a calendar for a "server." Using this program I need to have the client program connect to the server program, have the client wait for the server to respond through a socket, then exit and the server... (2 Replies)
I have asked this before but I haven't had any luck so far getting this to work. I use RCS(revision control system). When it runs if I pass the value 'unlock' to $3 its reassigned to $unlock. When I run the command (rcs -u'version number' 'filename') ti will ask me 1-(Do you want to break the lock... (5 Replies)
Hi, I was hoping for help with a for loop to run a program (vina) repeatedly using all the files in a folder as input. Currently my code looks like this:
#!/bin/bash
FILES=/home/afalk/Desktop/battest/*.pdbqt
for f in $FILES do
vina --config /home/afalk/Desktop/A.txt --ligand "$f".pdbqt
done... (5 Replies)
I need to run an interactive program in the background so I can grep it for specific data to use for some logic in a script.
There is no quiet or background mode on the program so I plan to redirect a document with commands in it and then to grep the output.
This is almost working, except... (1 Reply)
Hi all,
I am using an external binary to view memory starting from a specific address and i want to automate this via PERL however there are problems. Hope you can help me ..thx
The output of the programme is like below:
bash-3.2$ mem_disp 12B21D20 100
Opening RO Data Memory File scp.ro... (4 Replies)
Dear community,
I communicate with an external program (maxima) using named pipes. If I use a text file to capture the output (maxima > out.txt) i can see the programs answer directly after the input written into the file. But if bypass the output into a named pipe (maxima > pipe) and capture it... (1 Reply)
Discussion started by: Pustekuchen
1 Replies
LEARN ABOUT SUSE
system
SYSTEM(3) Linux Programmer's Manual SYSTEM(3)NAME
system - execute a shell command
SYNOPSIS
#include <stdlib.h>
int system(const char *command);
DESCRIPTION
system() executes a command specified in command by calling /bin/sh -c command, and returns after the command has been completed. During
execution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored.
RETURN VALUE
The value returned is -1 on error (e.g. fork(2) failed), and the return status of the command otherwise. This latter return status is in
the format specified in wait(2). Thus, the exit code of the command will be WEXITSTATUS(status). In case /bin/sh could not be executed,
the exit status will be that of a command that does exit(127).
If the value of command is NULL, system() returns nonzero if the shell is available, and zero if not.
system() does not affect the wait status of any other children.
CONFORMING TO
C89, C99, POSIX.1-2001.
NOTES
If the _XOPEN_SOURCE feature test macro is defined, then the macros described in wait(2) (WEXITSTATUS(), etc.) are made available when
including <stdlib.h>.
As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs that call it from a loop uninterruptible, unless they take care
themselves to check the exit status of the child. E.g.
while (something) {
int ret = system("foo");
if (WIFSIGNALED(ret) &&
(WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
break;
}
Do not use system() from a program with set-user-ID or set-group-ID privileges, because strange values for some environment variables might
be used to subvert system integrity. Use the exec(3) family of functions instead, but not execlp(3) or execvp(3). system() will not, in
fact, work properly from programs with set-user-ID or set-group-ID privileges on systems on which /bin/sh is bash version 2, since bash 2
drops privileges on startup. (Debian uses a modified bash which does not do this when invoked as sh.)
In versions of glibc before 2.1.3, the check for the availability of /bin/sh was not actually performed if command was NULL; instead it was
always assumed to be available, and system() always returned 1 in this case. Since glibc 2.1.3, this check is performed because, even
though POSIX.1-2001 requires a conforming implementation to provide a shell, that shell may not be available or executable if the calling
program has previously called chroot(2) (which is not specified by POSIX.1-2001).
It is possible for the shell command to return 127, so that code is not a sure indication that the execve(2) call failed.
SEE ALSO sh(1), signal(2), wait(2), exec(3)COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2004-12-20 SYSTEM(3)