Question

I have an application which had optional extras depending on if the user has the software installed.

On Linux what is the best way to determine if something like python and PyUsb is installed?

I am developing a C++ Qt application if that helps.

Answer 1

This is inefficient (requires forking and exec’ing /bin/sh). There has to be a better way! But as a generic approach… There’s always system().

(Remember to use WEXITSTATUS()! Watch out for making programs uninterruptable!)

#define SHOW(X)  cout << # X ' = ' << (X) << endl  int main() {   int status;    SHOW( status = system( 'which grep > /dev/null 2>&1' ) );   SHOW( WEXITSTATUS(status) );    SHOW( status = system( 'which no_matching_file > /dev/null 2>&1' ) );   SHOW( WEXITSTATUS(status) ); } 

There is also popen(), which can be useful for grabbing output from programs to verify version numbers, libraries, or whatnot.

If you need bidirectional (read&write) access to a subprocess, best to use pipe(), fork(), exec(), close(), & dup2().