print command and run it (like `make` does)

+.c

#include <stdio.h>

int main(int argc, char **argv)
{
        int i;
        printf( "+" );
        for( i = 1; i < argc; i++ )
                printf( " %s",  argv[i] );
        printf( "\n" );
        if( argc > 1 )
                execvp( argv[1], argv + 1 );
}

It works like this:

root@l3:~# + echo Hi
+ echo Hi
Hi
root@l3:~#