I have C program ( program.c ) that calls a shell script ( command.sh ).
command.sh returns an output (a password), i need to get this output in my program.c.
using system(command); , i can't get hold of the output.
is there any other way in C to solve my problem?
5 Answers
Not in pure C. You want POSIX. Specifically popen function.
The specification has a nice example, that you can just copy 1:1 http://pubs.opengroup.org/onlinepubs/009604499/functions/popen.html
2 Comments
Aymanadou
I hoped for a mechanism that uses the memory as intermediate between my program c and the script shell.I won't use files. Thank you
Šimon Tóth
@Aymanadou Well yes, this solution is using a PIPE, that's just a buffer.
Sounds like you're afraid to use libraries. Please try and use libraries, they're just as much part of Unix as shell tools.
Comments
In pure C (well ... ignoring the contents of the system() call) you can redirect the shell script output to a file, then read that file.
system("whatever > file");
handle = fopen("file", "r");
/* if ok use handle */
fclose(handle);
Comments
You can use popen() as suggested above, but note that in this case you have no control over the process you created (e.g. you will not be able to kill it), you also will not know its exit status.
I suggest using classical pipe/fork/exec combination. Then you will know the pid of your child process, so you will be able so send signals, also with pipe() you are able to redirect process standard output, so you can easily read it in your parent process. As example you can see my accepted answer to popen() alternative.
Comments
You should open a pipe using popen but this sounds tedious. A C program calling a shell script for a password.
system()(is this homework)?