Without the magic line, prove shows lots and lots of errors:
% prove ./t9804-git-p4-label.sh
./t9804-git-p4-label.sh .. syntax error at ./t9804-git-p4-label.sh line 3, near ". ."
...
When #!/bin/sh is added, tests are skipped (I have no p4d).
Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> Signed-off-by: Junio C Hamano <gitster@pobox.com>