executing a command and getting o/p to a variable

Question

popen stores o/p of the specified command into a file. How can I get similar functionality but o/p into a variable (i.e. in a char*) ?

Have a look a this question (pretty much, duplicate of yours): http://stackoverflow.com/questions/219138/get-command-output-in-pipe-c-for-linux — Aleks G, Jul 07 '11 at 08:03

score 1 · Answer 1 · answered Jul 07 '11 at 08:09

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No, popen() does not store output into a file. It specifies a stream, which might represent to a file on disk but which might also be at e.g. a pipe or socket. Streams are more abstract than files.

To have a pipe, you would open the pipe using e.g. pipe() and then call fdopen() on the proper end of the resulting pipe.

answered Jul 07 '11 at 08:09

unwind

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Thanks unwind. What I want to do is to be able to execute a very simple thing i.e. `wc -l filename` and store the o/p in a variable/buffer. Possible? – hari Jul 07 '11 at 08:24

score 1 · Accepted Answer · answered Jul 07 '11 at 17:41

I could not find anything that returns o/p in a variable. It kind of makes sense as some commands' o/p can be large so to make the behavior consistent, o/p is stored in the file. I actually ended up reading from file returned by popen.

Thanks for all the help.

score 0 · Answer 3 · answered Jul 07 '11 at 08:02

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you can replace STDOUT and STDERR for the launched command with a stream that you control

answered Jul 07 '11 at 08:02

Jim Deville

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score 0 · Answer 4 · answered Jul 07 '11 at 10:11

Do you want to run a unix command from a C program, and store the output?

If so, then the sequence is to call FILE* pipe = popen("wc -l filename", "r"); and then read from the FILE* pipe just as you would read from a file opened using fopen. That is, you use functions like fgets or fscanf to read the output, just as you would if the output of the command were in a file.

executing a command and getting o/p to a variable

4 Answers4