--- a/runtest
+++ b/runtest
@@ -3,7 +3,7 @@ TCL_VERSIONS="8.5 8.6 9.0"
 TCLSH=""
 
 for VERSION in $TCL_VERSIONS; do
-	TCL=`which tclsh$VERSION 2>/dev/null` && TCLSH=$TCL
+	TCL=`command -v tclsh$VERSION 2>/dev/null` && TCLSH=$TCL
 done
 
 if [ -z $TCLSH ]
--- a/runtest-moduleapi
+++ b/runtest-moduleapi
@@ -4,7 +4,7 @@ TCLSH=""
 [ -z "$MAKE" ] && MAKE=make
 
 for VERSION in $TCL_VERSIONS; do
-	TCL=`which tclsh$VERSION 2>/dev/null` && TCLSH=$TCL
+	TCL=`command -v tclsh$VERSION 2>/dev/null` && TCLSH=$TCL
 done
 
 if [ -z $TCLSH ]
--- a/runtest-sentinel
+++ b/runtest-sentinel
@@ -3,7 +3,7 @@ TCL_VERSIONS="8.5 8.6 9.0"
 TCLSH=""
 
 for VERSION in $TCL_VERSIONS; do
-	TCL=`which tclsh$VERSION 2>/dev/null` && TCLSH=$TCL
+	TCL=`command -v tclsh$VERSION 2>/dev/null` && TCLSH=$TCL
 done
 
 if [ -z $TCLSH ]
--- a/src/Makefile
+++ b/src/Makefile
@@ -68,7 +68,7 @@ INSTALL=install
 PKG_CONFIG?=pkg-config
 
 ifndef PYTHON
-PYTHON := $(shell which python3 || which python)
+PYTHON := $(shell command -v python3 || command -v python)
 endif
 
 # Default allocator defaults to Jemalloc on Linux and libc otherwise
--- a/utils/generate-module-api-doc.rb
+++ b/utils/generate-module-api-doc.rb
@@ -241,7 +241,7 @@ end
 # Populate the 'since' map (name => version) if we're in a git repo.
 require "./" ++ File.dirname(__FILE__) ++ '/module-api-since.rb'
 git_dir = File.dirname(__FILE__) ++ "/../.git"
-if File.directory?(git_dir) && `which git` != ""
+if File.directory?(git_dir) && `command -v git` != ""
     `git --git-dir="#{git_dir}" tag --sort=v:refname`.each_line do |git_tag|
         next if git_tag !~ /^(\d+)\.(\d+)\.(\d+)(?:-rc\d+)?$/ || $1.to_i < 7
         # Version number, ignoring suffixes like -rc1.