When I'm executing ping4 linux.com in a bash terminal on Linux Mint 22.1 Kernel 6.8.0.55 the URL is resolved to a IPv4 address, when executing ping6 linux.com the URL is resolved to a IPv6 adress as expected. As which shows, both, ping4 and ping6, are symbolic links in /usr/bin/ to ping (also in /usr/bin/).
So where comes the information for ping from, that it is called via ping4 or ping6? Calling ping4 -6 linux.com or ping6 -4 linux.com both result in only one -4 or -6 option may be specified
I would expect that ping4 and ping6 behave the same way as ping, because they are only symbolic links to ping.
If it is the iputils version of ping:
/* Support being called using `ping4` or `ping6` symlinks */
if (argv[0][strlen(argv[0]) - 1] == '4')
hints.ai_family = AF_INET;
else if (argv[0][strlen(argv[0]) - 1] == '6')
hints.ai_family = AF_INET6;
and later:
case '4':
if (hints.ai_family == AF_INET6)
error(2, 0, _("only one -4 or -6 option may be specified"));
hints.ai_family = AF_INET;
break;
Even if you don't know the language that a program is written in, skimming its source can give useful information.