fixed regression if SHELL=zsh

which.spec

@@ -1,7 +1,7 @@
 Summary: Displays where a particular program in your path is located
 Name: which
 Version: 2.21
-Release: 23%{?dist}
+Release: 24%{?dist}
 License: GPLv3
 Source0: http://ftp.gnu.org/gnu/which/%{name}-%{version}.tar.gz
 Source1: which2.sh
@@ -40,6 +40,9 @@ rm -f $RPM_BUILD_ROOT%{_infodir}/dir
 %{_mandir}/man1/which.1*
 
 %changelog
+* Tue Mar 23 2021 Than Ngo <than@redhat.com> - 2.21-24
+- fixed regression if SHELL=zsh
+
 * Sun Mar 21 2021 Than Ngo <than@redhat.com> - 2.21-23
 - fixed coverity issues
 - improved which2.sh

which2.sh

@@ -1,9 +1,11 @@
+# shellcheck shell=sh
 # Initialization script for bash, sh, mksh and ksh
 
 _declare="declare -f"
 _opt="-f"
+_shell="$(basename $SHELL)"
 
-if [ "$0" = "ksh" ] || [ "$0" = "-ksh" ] || [ "$0" = "mksh" ] || [ "$0" = "-mksh" ] ; then
+if [ "$_shell" = "ksh" ] || [ "$_shell" = "mksh" ] || [ "$_shell" = "zsh" ] ; then
   _declare="typeset -f"
   _opt=""
 fi