Send Linux command from C program

Question

I'm writing a C program to run in Linux shell. Now I got a problem with such command.

#include <stdio.h>
void main()
{
char* command="history>>history";
system(command);
}

I want it to write the result of command "history" into a document, but it failed with a blank one.

If I change it to "date>>history", current system time will be written into the document.

Is there any problem with "history>>history"? What should I do if I want to get that work? Thanks!

run which history and observe that it is... probably a shell builtin — mnagel
– mnagel, Commented Aug 4, 2013 at 20:14
if date writes to history, then maybe history doesn't write anything to stdout so you can redirect it with >> to a file, — Radu Chivu
– Radu Chivu, Commented Aug 4, 2013 at 20:16
Sorry, I want it to save the result of "history" to a document names "history". — Jiayi Guo
– Jiayi Guo, Commented Aug 4, 2013 at 20:16
is there a reason why you're using C for this, rather than a bash function? — Will Palmer
– Will Palmer, Commented Aug 4, 2013 at 20:43

Pik' · Accepted Answer · 2013-08-04 20:17:04Z

5

The problem is that history is not a real command but a shell builtin. Thus you can't call it from a C program[1].

Depending on the shell the user is using, you can instead get the history from ~/.bash_history, ~/.zsh_history and so on. Note however that zsh only write to this file at the end of a session.

[1] Well, you could theorically try system("bash -c history"), but you won't get the actual history because the builtin isn't run in the context of the current session.

answered Aug 4, 2013 at 20:17

Pik'

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1 Comment

Jiayi Guo Over a year ago

Thank you for figuring out!

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