get failed output back

Question

I'm trying to run a script and output the result in the console. It works, but there is a

small problem i'm facing right now. If the "script" file is writed/coded wrong i get as output something like:

 syntax error, unexpected $undefined, expecting $end puts

which is very good that it tells me somehting is wrong with the code inside the script file, but in my code line:

printf("%s", path);

it dosent print that to me and i want it to print it so i can display it on the screen. Please help me out

 fp = popen("our script...is here", "r");
    if (fp == NULL)
        /* Handle error */;


    while (fgets(path, PATH_MAX, fp) != NULL)
        printf("%s", path);


    status = pclose(fp);

Ps: just to make it more clear i'm using xcode and dont mind the code in C or C++

Possible duplicate with http://stackoverflow.com/questions/280571/how-to-control-popen-stdin-stdout-stderr-redirection and with http://stackoverflow.com/questions/6900577/c-popen-wont-catch-stderr — MOHAMED, Dec 26 '12 at 15:17

score 1 · Answer 1 · answered Dec 26 '12 at 15:05

1

You have to care about the stderr - popen() handled only stdout:

Conversely, reading from a "popened" stream reads the command's standard output,

The shell error will be printed to stderr - which popen() does not handle.

answered Dec 26 '12 at 15:05

Andreas Florath

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If you don't mind me asking, could you please give a example on how to use it in the code to avoid any other problems and to also help others?? – Alexandra Sjoslavma Dec 26 '12 at 15:07
Ok - then I'll not finish the example - looks that one solution is already accepted. – Andreas Florath Dec 26 '12 at 15:22
Thnaks alot for your time, but someone already had a good solution. :) – Alexandra Sjoslavma Dec 26 '12 at 15:23
I'm just wondering how you want to decide if the script exited with or without error. Typically you have to distinguish between stdout and stderr - but if this fits your needs, it's ok. – Andreas Florath Dec 26 '12 at 15:32

score 1 · Accepted Answer · answered Dec 26 '12 at 15:12

1

By default fgets() reads only from stdout of the stream. To capture stderr, you can simply redirect it to stdout:

 fp = popen("./script 2>&1", "r");

Now both the stdout and stderr will go stdout which your C code can read from.

Note that once you have redirected as above there's no way to differentiate stdout and stderr.

answered Dec 26 '12 at 15:12

P.P

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Can i get a complete example? please. As i know how to load the script, but need to print what wrong also – Alexandra Sjoslavma Dec 26 '12 at 15:14
All you need to do change the one line as above and have some syntax errors in your script to test it. – P.P Dec 26 '12 at 15:15

get failed output back

2 Answers2