refactor: use regex matching instead of for loop

Instead of creating a for-loop where we go through each argument, to
check if current argument is -m and next argument is pip, we instead do
simple regex matching where we look for ` -m pip ` somewhere in the
command which is to be executed.

pyenv.d/exec/pip-rehash.bash

@@ -6,13 +6,10 @@ if [[ $PYENV_REHASH_COMMAND =~ ^(pip|easy_install)[23](\.\d)?$ ]]; then
   PYENV_REHASH_COMMAND="${BASH_REMATCH[1]}"
 fi
 
-for (( i=1; i<$#; i++ )); do
-  next=$((i+1))
-  if [[ ${!i} == "-m" && ${!next} == "pip" ]]; then
+# Check for ` -m pip ` in arguments
+if [[ "$*" =~ [[:space:]]-m[[:space:]]pip[[:space:]] ]]; then
   PYENV_REHASH_COMMAND="pip"
-    break
-  fi
-done
+fi
 
 if [ -x "${PYENV_PIP_REHASH_ROOT}/${PYENV_REHASH_COMMAND}" ]; then
   PYENV_COMMAND_PATH="${PYENV_PIP_REHASH_ROOT}/${PYENV_REHASH_COMMAND##*/}"