SYSTEM(3) BSD Library Functions Manual SYSTEM(3)NAME
system -- pass a command to the shell
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
int
system(const char *string);
DESCRIPTION
The system() function hands the argument string to the command interpreter sh(1). The calling process waits for the shell to finish execut-
ing the command, ignoring SIGINT and SIGQUIT, and blocking SIGCHLD.
If string is a NULL pointer, system() will return non-zero if the command interpreter sh(1) is available, and zero if it is not.
RETURN VALUES
The system() function returns the exit status of the shell as returned by waitpid(2), or -1 if an error occurred when invoking fork(2) or
waitpid(2). A return value of 127 means the execution of the shell failed.
SEE ALSO sh(1), execve(2), fork(2), waitpid(2), popen(3)STANDARDS
The system() function conforms to ISO/IEC 9899:1990 (``ISO C90'') and is expected to be IEEE Std 1003.2 (``POSIX.2'') compatible.
BSD June 4, 1993 BSD
Check Out this Related Man Page
SYSTEM(3) Linux Programmer's Manual SYSTEM(3)NAME
system - execute a shell command
SYNOPSIS
#include <stdlib.h>
int system(const char *string);
DESCRIPTION
system() executes a command specified in string by calling /bin/sh -c string, 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 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 string 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
ANSI C, POSIX.2, BSD 4.3
NOTES
As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs that call it from a loop uninterruptable, 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 suid or sgid 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 suid or sgid 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.)
The check for the availability of /bin/sh is not actually performed; it is always assumed to be available. ISO C specifies the check, but
POSIX.2 specifies that the return shall always be non-zero, since a system without the shell is not conforming, and it is this that is
implemented.
It is possible for the shell command to return 127, so that code is not a sure indication that the execve() call failed.
SEE ALSO sh(1), signal(2), wait(2), exec(3)
2001-09-23 SYSTEM(3)
When i try to execute some shell command from my C program using system(), how can I capture the
error that occurs due to the shell command?
The system() command's return values will say if the system() was successfull and not if the shell command is successfull.
When I tested my program, I... (3 Replies)
i'm pretty new to unix programming. i just wanna know how exactly fork(), waitpid() works. i have read some from the book, but it's still confusing. especially with those < 0 and == 0. plz help!!!! (1 Reply)
Hello all,
Got a question to ask, in some OS, if a shell command is not an internal command, then it is assumed to be a separate program which is loaded into the memory of the computer and then executed.
In UNIX a different technique is used which does much the same sort of thing. What is the... (2 Replies)
Can anybody help me for writing unix shell scripting on fork();
it will be appreciated, if any body can send me sample, tutorial ...with details. (5 Replies)
What is the difference between the(a) shell and the (a) command-line interpreter?
Here we're talking about the complete dummy question, but could someone point me right.
(yes, have written scripts in for instance bash shell,
and and grepp-ed my way around ....:eek: (4 Replies)
Hi guys,
So my code is below. This is a simplified version of the shell... It does not continue for ever... I guess its actually rather a program to accept a command.. has the fork and the execve etc. Anyways when i compile it and run it in the terminal for some reason only '/bin/echo "enter... (1 Reply)
Hi Guys,
Just a question about subprocesses.. Lately one of our servers has started to throw out the following error:
SYSTEM ERROR: Too many subprocesses, cannot fork. Errno=12
We've already increased the threshold twice. Its now up to 8000 and the swap space has also been increased. We... (6 Replies)
The man system says
During execution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored.
What does this mean?
And if i am making a function that does what system does how do i write this signal stuff? (19 Replies)
Hi folks, I am writing a simple program to understand how fork() and waitpid works, but it doesn't seem that is working like I wanted.
if(fork()==0){
//el hijo
pid1=getpid();
printf("\nSoy el hijo %d",pid1);
}else {
//el padre
if (fork()==0) {
//el hijo
pid2=getpid();... (2 Replies)
Hi, I'm writing a shell script where I want to call fork(). However I wrote like this "var=fork()" in c style and got this error:
"syntax error near unexpected token `(' "
How could I call fork() in shell script? Thanks in advance.
Duplicate Post - Continue Here - Please Do Not Cross Post... (0 Replies)
Hello, I'm currently implementing the && function in a shell using C. For example, if we input cmd1 && cmd2, then cmd2 executes only when cmd1 exits successfully. I'm thinking about:
int main() {
int i;
char **args;
while(1) {
printf("yongfeng's shell:~$ ");
args =... (5 Replies)
I have a running service which runs in background.
It execute shell commands by function system(cmd)
I need to report fail when command execution takes more than 60 seconds.
Parent doesn't need to wait for 60 seconds of time if the cmd execution completed already.
runCommand()
{
pid_t... (3 Replies)
Hi All,
I am having below hdfs file system
/user/home/dte=2019_01_30/part_1
/user/home/dte=2019_01_30/part_2
/user/home/dte=2019_01_31/part_1
I need to take the latest month hdfs folder while passing date as parameter.
For eg . if i pass as Feb month i.e. 20190201(YYYYMMDD), then... (0 Replies)