如何捕获特定的linux系统返回

Question

I recently started to use linux, so I have little knowledge about it. At least I know that every thing in linux is a file.

I would like to know how to catch a specific linux system return, for example if I choose install ruby (sudo apt-get -y install ruby), how can I know it was installed successfully?

char buffer[1024];
char *buf = malloc(4096);

char *pl;
FILE *fp;

if (strcmp(cmd, "ruby") == 0)
{
        fp = popen("sudo apt-get -y install ruby", "r");
}

if (fp == NULL)
{
        printf("Failed to load file\n");
        exit(0);
}

while ((pl = fgets(buffer, sizeof(buffer), fp)) != NULL)
{
        strcat(buf, buffer);
}

strcat(buf, "\n");

pclose(fp);

Then I am using popen to read the file opened, but it contains the same that is shown in terminal and I just want a 'flag' like OK or FAIL.

Sorry for my poor english.

Answer 1

The exit code of apt-get will tell you if it succeeded or not (0 means success). pclose(fp) will return the exit code, so you can do:

if (pclose(fp) == 0) {
  // success
} else {
  // failure
}  

You may notice, though, that now we're not actually reading from the pipe. There's not really any reason to have it. So like Joachim suggested, the system() function is probably a better fit for your case.

Answer 2

You need to check the exit status from the program being run. See: http://linux.die.net/man/3/popen

The pclose() function waits for the associated process to terminate and returns the
exit status of the command as returned by wait4(2).

Every process provides an exit status (an integer, from 0 to 255) that indicates how/why the program ended. 0 is typically used for a normal (successful) execution, this one is the one you should be looking for.

Try to see the manual page for apt-get or googling for the correct exit codes for apt-get.

Hope it helps!