expr: unexpected argument error for missing arguments is misleading

[cakebaker]

The following commands lead to unexpected argument errors with uutils expr:

$ cargo run expr length
expr: syntax error: unexpected argument 'length'
$ cargo run expr index hello
expr: syntax error: unexpected argument 'index'
$ cargo run expr substr hello 1
expr: syntax error: unexpected argument 'substr'

This is a bit misleading because the problem is not the argument shown in the error message but missing arguments.

GNU expr shows a missing argument error in such cases:

$ expr length
expr: syntax error: missing argument after ‘length’
$ expr index hello
expr: syntax error: missing argument after ‘hello’
$ expr substr hello 1
expr: syntax error: missing argument after ‘1’

[Luv-Ray]

Now they all leading to expr: syntax error (premature end of expression) on the main branch of uutils:

$ cargo run expr length
expr: syntax error (premature end of expression)
$ cargo run expr index hello
expr: syntax error (premature end of expression)
$ cargo run expr substr hello 1
expr: syntax error (premature end of expression)

Is this acceptable?

[tertsdiepraam]

That doesn't sound like the right behaviour. I'm reworking the parsing at the moment though. I'll try to get that PR up soon.

[tertsdiepraam]

Fixed by #5586