Envir. variables into C program

**ojschubert** · 02-06-2005

Hello,

I'm fairly new to both linux and C programming so this might be a stupid question.

I'm trying to write a C program that calls a shell script which does an scp and also sets an environment variable.

Then I would like to use this variable in my C program. The problem is that I can't get those evironment variables into my C program for some reason. What am I doing wrong?

Here is my C program:

Code:

#include <stdio.h>
#include <stdlib.h>

int main (int argc, char *argv[], char *envp[])
{
                system(". getfile");	 	
                printf("ojeniv var is %s\n",envp[16]);		return 0;
}

I know there has got to be a better way to get at my environmental variable "ojeniv" than envp[16] but it's the best I could do for now.

Here is the script (getfile) that it called:

Code:

    #/bin/bash
    scp zephost:/root/signal /home/oj/junk/signal
    ojeniv=`grep seg2 /home/oj/junk/signal | gawk '{print$2}'`
    echo $ojeniv
    export ojeniv=$ojeniv

It seems like when I run the C program the environment variable will not be set. It will only change if i do a ". getfile" . What's going on here?

Any help is appreciated

Thanks

**quzah** · 02-06-2005

Code:

#include <stdio.h>

int main( int argc, char *argv[], char *env[] )
{
        int x;
        for( x = 0; env[x]; x++ )
                printf("%s\n", env[x] );
        return 0;
}

Also consider 'man 3 getenv'.

Quzah.

**Salem** · 02-07-2005

Environment variables are inherited only from a parent process to a child process.
So invoking a child process and then trying to read it's environment after it has quit simply isn't going to work.

I suggest something like this for your script. Note that the output is sent to stdout, not some variable.

Code:

#!/bin/bash
scp zephost:/root/signal /home/oj/junk/signal
grep seg2 /home/oj/junk/signal | gawk '{print$2}'

In your C code, you do this

Code:

int main ( ) {
    char buff[BUFSIZ]
    FILE *fp = popen( "./getfile", "r" );  /* run a process, and read it's stdout */
    while ( fgets( buff, BUFSIZ, fp ) != NULL ) {
        /* buff contains successive lines of the output of the process you invoked */
    }
    pclose( fp );
    return 0;

**ojschubert** · 02-07-2005

Works like a charm Salem.

I don't see how the output of my script gets into stdout but I'll look into that.

Thanks a lot,
oj

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