`command -v` portability

The "which" utility is not guaranteed to be installed, and if it is, its behavior is not portable.

Conversely, the "command -v" shell builtin is required to exist in all POSIX 2008 compliant shells, and is thus guaranteed to work everywhere.

Examples of open-source shells likely to be installed as /bin/sh on Linux, which implement the 12-year-old standard: ash, bash, busybox, dash, ksh, mksh and zsh.

A side benefit of using the POSIX portable option is that it does not require an external disk executable to be forked. This therefore represents a mild speedup.

scripts/xdg-email.in

@@ -90,7 +90,7 @@ open_kde()
         local kreadconfig=kreadconfig
     fi
 
-    if which $kreadconfig >/dev/null 2>&1; then
+    if command -v $kreadconfig >/dev/null; then
         local profile=$($kreadconfig --file emaildefaults \
                                      --group Defaults --key Profile)
         if [ -n "$profile" ]; then
@@ -98,7 +98,7 @@ open_kde()
                                         --group "PROFILE_$profile" \
                                         --key EmailClient \
                                   | cut -d ' ' -f 1)
-            if [ -z "${client%%*.desktop}" ] && ! which "$client" >/dev/null 2>&1; then
+            if [ -z "${client%%*.desktop}" ] && ! command -v "$client" >/dev/null 2>&1; then
                 client=`desktop_file_to_binary "$client"`
             fi
 
@@ -115,7 +115,7 @@ open_kde()
         *) command=kde-open$KDE_SESSION_VERSION ;;
     esac
 
-    if which $command >/dev/null 2>&1; then
+    if command -v $command >/dev/null; then
         DEBUG 1 "Running $command \"$1\""
         if [ "$KDE_SESSION_VERSION" = 3 ]; then
             # KDE3 uses locale's encoding when decoding the URI,
@@ -435,7 +435,7 @@ mailto=`echo "${mailto}"| sed 's/[?&]$//'`
 # Shouldn't happen
 [ x"${mailto}" != x"" ] || exit_failure_syntax
 
-if which @NAME@-hook.sh > /dev/null 2> /dev/null; then
+if command -v @NAME@-hook.sh > /dev/null; then
     @NAME@-hook.sh "${mailto}"
     if [ $? -eq 0 ]; then
         exit_success