#!/bin/sh if [ Foo.java -nt Foo.class ] then javac Foo.java fi
The easiest fix is to switch to a shell that does support
-nt, like bash:
#!/bin/bash if [ Foo.java -nt Foo.class ] then javac Foo.java fi
find can be used:
#!/bin/sh if [ -n "$(find Foo.java -newer Foo.class)" ] then javac Foo.java fi
test -nt is an extension in ksh, bash and dash, but it is not covered by POSIX.
If you only intend to target shells that supports this feature, you can change the shebang to a shell that guarantees support, or ignore this warning.
You can use
# shellcheck disable=SC3000-SC4000 to ignore all such compatibility warnings.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.