Changing argv[0] from the command line

Question

I remember many years (decades) ago using a system where one could say something like:

$ realname:newname A B C

and the program would be invoked with argv = { "newname", "A", "B", "C" }.

I don't remember what shell this was though.

Does such a capability exist in any current shells?

UPDATE:

exec -a looked like it was what I wanted, but I'm getting inconsistent behaviour depending upon the program's language (yes, I know it's awful code):

$ cat argv.c  && cc argv.c
int main(int argc, char **argv) { printf("<< %s >>\n", argv[0]); }

$ (exec -a fake ./a.out)
<< fake >>

It works fine in "C", but not in python:

$ cat argv.py
#!/usr/bin/python3
import sys
print("<<", sys.argv[0], ">>")

$ (exec -a fake ./argv.py)
<< /home/ray/test/argv.py >>

Answer 1

When starting a shell using its -c option to run an in-line script, the first argument will be placed in $0:

$ sh -c 'printf "0: %s\n" "$0"; printf "Other: %s\n" "$@"'  hello there how are you
0: hello
Other: there
Other: how
Other: are
Other: you

In bash, assigning to BASH_ARGV0 changes the current shell's $0 value:

$ printf '%s\n' "$0"
/usr/local/bin/bash
$ BASH_ARGV0="hello"
$ printf '%s\n' "$0"
hello

(but it does not change the process' name on my system)

Using set, you'd change the other arguments:

$ printf '%s\n' "$@"

$ set -- A B C
$ printf '%s\n' "$@"
A
B
C

Answer 2

A symlink maybe enought for most systems:

~$ cat test.c 
#include <stdio.h>

int main(int ac, char **av)
{
    printf("%s\n", av[0]);
}
~$ cc -o test test.c
~$ ./test 
./test
~$ ln -s test coincoin 
~$ ./coincoin 
./coincoin

This is the mechanism used by busybox (widely used in embedded systems) to implement several utilities (ping, route, etc...) using only one binary.

Answer 3

[not a real answer yet]

When used with a she-banged executable script, neither

execl("/path/to/script", "new_av0", (void*)0)

in C, nor

exec -a new_av0 /path/to/script

in shells which support exec -a will be able to set $0 or sys.argv[0] (or whatever language syntax is used to refer to the zeroth argument) in that script.

When executing the interpreter of a she-banged script, the kernel will irretrievably discard the original zeroth argument, splicing in its place the name of the interpreter, any optional she-bang line argument, and the path to the script.

Any solution is bound to be tricky, limited or language/system dependent.

For instance, a shell script could be fooled with:

sh -c '. /path/to/script' new_av0

But obviously, this will not affect the command line as it appears in the output of ps, /proc/<pid>/cmline, etc.