trap myfunc 28
trap myfunc WINCH
Signal numbers can vary between platforms. Prefer signal names, which are fixed.
Signal numbers 1, 2, 3, 6, 9, 14 and 15 are specified as parts of the optional POSIX XSI and ShellCheck will not warn about these.
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.