Merge pull request #11149 from duglin/8667-AdvancedVars

Add support for advanced ${} uses

builder/shell_parser.go

@@ -157,7 +157,40 @@ func (sw *shellWord) processDollar() (string, error) {
 			sw.next()
 			return sw.getEnv(name), nil
 		}
-		return "", fmt.Errorf("Unsupported ${} substitution: %s", sw.word)
+		if ch == ':' {
+			// Special ${xx:...} format processing
+			// Yes it allows for recursive $'s in the ... spot
+
+			sw.next() // skip over :
+			modifier := sw.next()
+
+			word, err := sw.processStopOn('}')
+			if err != nil {
+				return "", err
+			}
+
+			// Grab the current value of the variable in question so we
+			// can use to to determine what to do based on the modifier
+			newValue := sw.getEnv(name)
+
+			switch modifier {
+			case '+':
+				if newValue != "" {
+					newValue = word
+				}
+				return newValue, nil
+
+			case '-':
+				if newValue == "" {
+					newValue = word
+				}
+				return newValue, nil
+
+			default:
+				return "", fmt.Errorf("Unsupported modifier (%c) in substitution: %s", modifier, sw.word)
+			}
+		}
+		return "", fmt.Errorf("Missing ':' in substitution: %s", sw.word)
 	}
 	// $xxx case
 	name := sw.processName()

builder/words

@@ -30,6 +30,17 @@ he${hi}                  |     he
 he${hi}xx                |     hexx
 he${PWD}                 |     he/home
 he${.}                   |     error
+he${XXX:-000}xx          |     he000xx
+he${PWD:-000}xx          |     he/homexx
+he${XXX:-$PWD}xx         |     he/homexx
+he${XXX:-${PWD:-yyy}}xx  |     he/homexx
+he${XXX:-${YYY:-yyy}}xx  |     heyyyxx
+he${XXX:YYY}             |     error
+he${XXX:+${PWD}}xx       |     hexx
+he${PWD:+${XXX}}xx       |     hexx
+he${PWD:+${SHELL}}xx     |     hebashxx
+he${XXX:+000}xx          |     hexx
+he${PWD:+000}xx          |     he000xx
 'he${XX}'                |     he${XX}
 "he${PWD}"               |     he/home
 "he'$PWD'"               |     he'/home'
@@ -41,3 +52,7 @@ he\$PWD                  |     he$PWD
 "he\$PWD"                |     he$PWD
 'he\$PWD'                |     he\$PWD
 he${PWD                  |     error
+he${PWD:=000}xx          |     error
+he${PWD:+${PWD}:}xx      |     he/home:xx
+he${XXX:-\$PWD:}xx       |     he$PWD:xx
+he${XXX:-\${PWD}z}xx     |     he${PWDz}xx