Can argc be zero on a POSIX system?

Question

Given the standard definition for the main program:

int main(int argc, char *argv[]) {
   ...
}

Under which circumstances can argc

Answer 1

Early proposals required that the value of argc passed to main() be "one or greater". This was driven by the same requirement in drafts of the ISO C standard. In fact, historical implementations have passed a value of zero when no arguments are supplied to the caller of the exec functions. This requirement was removed from the ISO C standard and subsequently removed from this volume of POSIX.1-2017 as well. The wording, in particular the use of the word should, requires a Strictly Conforming POSIX Application to pass at least one argument to the exec function, thus guaranteeing that argc be one or greater when invoked by such an application. In fact, this is good practice, since many existing applications reference argv[0] without first checking the value of argc.

The requirement on a Strictly Conforming POSIX Application also states that the value passed as the first argument be a filename string associated with the process being started. Although some existing applications pass a pathname rather than a filename string in some circumstances, a filename string is more generally useful, since the common usage of argv[0] is in printing diagnostics. In some cases the filename passed is not the actual filename of the file; for example, many implementations of the login utility use a convention of prefixing a ( '-' ) to the actual filename, which indicates to the command interpreter being invoked that it is a "login shell".

Also, note that the test and [ utilities require specific strings for the argv[0] argument to have deterministic behavior across all implementations.

Source

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Can argc be zero on a POSIX system?

Yes but it would not be strictly conforming to POSIX.