lp and lpr wrapper to disable -U command line argument

README.md

LP Wrapper

The Linux Command line tools lp and lpr provide the parameter -U which gives a user the ability to switch into the role of another user. This bypasses the possibility to track the amount of printed pages in a large university network. Therefore a wrapper-program was designed which filters the list of arguments and removes a -U if it can be found. The compiled binaries have to be installed at a location which is higher ranked in the $PATH variable than the original binaries.

installation

By Calling $make the source code will be compiled and with $sudo make install after compilation the binaries will be copied into the right location. Make sure that /usr/local/bin is located in the $PATH variable.

main.cpp

#include <iostream>
#include <cstring>
#include <unistd.h>
using namespace std;

int main(int argc, char * argv[])
{
	char * new_argv[ argc + 1 ] = {NULL};
	unsigned int removed_from_argc = 0;

	for(int i = 0; i < argc; i++) { // run through all command line parameters
		if( strcmp( argv[i], "-U" ) == 0 ) { // search for a "-U" command line parameter
			// skip the -U parameter from the list of new parameters and memorize that the ammount of parameters is now smaller
			removed_from_argc++;

			if( (i + 1) < argc ) {
				// Remove also the next value if there is one
				i++;
				removed_from_argc++;
			}
		} else if( strlen(argv[i]) > 2 && ( argv[i][0] == '-' ) && ( argv[i][1] == 'U' ) ) { // search for a "-U..." and remove only this one, keep all following
			// skip the -U parameter from the list of new parameters and memorize that the ammount of parameters is now smaller
			removed_from_argc++;
		}else {
			new_argv[i - removed_from_argc] = argv[i];
		}
	}

	// execv() now with the right set of parameters
#ifdef LP
	char path_to_exec[] = "/usr/bin/lp";
	char name_exec[] = "lp";
#endif
#ifdef LPR
	char path_to_exec[] = "/usr/bin/lpr";
	char name_exec[] = "lpr";
#endif
	new_argv[0] = name_exec;
	execv(path_to_exec, new_argv);
}

Makefile

CC=g++

main:
	$(CC) -D LP main.cpp -o lp
	$(CC) -D LPR main.cpp -o lpr

clean:
	rm lp_wrapper
	rm lpr_wrapper

instal: main
	mkdir -p /usr/local/bin
	cp ./lp /usr/local/bin
	chmod +x /usr/local/bin/lp
	cp ./lpr /usr/local/bin
	chmod +x /usr/local/bin/lpr