Refactor program_exists and program_must_exist

`program_must_exist` uses `program_exists` now, instead of repeating code. Changed `type` to `command -v` in `program_exists` to be more POSIX compliant. Refactored status code conditional in `program_exists` to remove double negatives. Thanks to @mkwmms for the suggestions.

Author: bronzehedwick

bootstrap.sh

@@ -47,22 +47,21 @@ debug() {
 
 program_exists() {
     local ret='0'
-    type $1 >/dev/null 2>&1 || { local ret='1'; }
+    command -v $1 >/dev/null 2>&1 || { local ret='1'; }
 
     # fail on non-zero return value
-    if [ ! "$ret" -eq '0' ]; then
+    if [ "$ret" -ne 0 ]; then
         return 1
     fi
 
     return 0
 }
 
 program_must_exist() {
-    local ret='0'
-    type $1 >/dev/null 2>&1 || { local ret='1'; }
+    program_exists $1
 
     # throw error on non-zero return value
-    if [ ! "$ret" -eq '0' ]; then
+    if [ "$?" -ne 0 ]; then
         error "You must have '$1' installed to continue."
     fi
 }