# [pjb@despina :0.0 c]$ make arg0
cc     arg0.c   -o arg0
# [pjb@despina :0.0 c]$ ./arg0
argv[0]=./arg0
# [pjb@despina :0.0 c]$ ( PATH=$(pwd) ; arg0 )
argv[0]=arg0
# [pjb@despina :0.0 c]$ $(pwd)/arg0
argv[0]=/Users/pjb/src/c/arg0
# [pjb@despina :0.0 c]$ cat arg0.c
#include <stdio.h>
int main(int argc,char* argv[]){
    printf("argv[0]=%s\n",argv[0]);
    return 0;
}
# [pjb@despina :0.0 c]$

# [pjb@despina :0.0 c]$ cat arg0.c
#include <stdio.h>
#include <unistd.h>
int main(int argc,char* argv[]){
    if(argc>1){
        char* pname=argv[0];
        argv[0]="You're fucked";
        execv(pname,argv);
    }
    printf("argv[0]=%s\n",argv[0]);
    return 0;
}
# [pjb@despina :0.0 c]$ make arg0
cc     arg0.c   -o arg0
# [pjb@despina :0.0 c]$ ./arg0 foo
argv[0]=You're fucked
# [pjb@despina :0.0 c]$