Improve handling of var references in vars file

Previously, if a previously defined variable was used as a value in a
variable assignment, it had to stand alone. This change allows variables
to be freely intermixed with text and multiple variables to be used in
a single assignment.

4 files changed, 45 insertions, 28 deletions

diff --git a/README.md b/README.md
index 48d0afc..3beb3ed 100644
--- a/README.md
+++ b/README.md
@@ -4,32 +4,37 @@ This is an extremely simple, general-purpose templating script written in awk.
 
 To get started, define a list of variables in a file:
 
-    food = pizza
-    beverage = coffee
+	# This is a comment.
+	food = pizza
+	beverage = coffee
+
+	# Previously defined variables can be used in variable definitions.
+	# Whitespace is optional inside braces.
+	dinner = {{ food }} and {{beverage}}
 
-    # Comments look like this, and you can reference previously defined
-    # variables like this:
-    dinner = {{ food }}
+	# The = character can be surrounded by any number of whitespace
+	# characters.
+	one	= 1
+	two	= 2
+	three=3
 
 Then reference those variables in your template file by enclosing them in
 double braces:
 
-    My favorite food is {{ food }}, and my favorite beverage is {{ coffee }}.
+	My favorite food is {{ food }}, and my favorite beverage is
+	{{ beverage }}. I'm going to have {{ dinner }} for dinner tonight.
+
+	The first three numbers are {{one}}, {{two}}, and {{three}}. {{one}} is
+	the smallest of the three.
 
 Then pass your variable file and template file, in that order, as arguments to
-the `template` script:
+the `template` script. To see the examples above in action, run the following
+command:
 
-    ./template vars favorite-foods.tpl
+    ./template example/vars example/text.tpl
 
 The result will be written to stdout.
 
-## Example
-
-The `example` directory provides concise sample files that can be processed by
-running the following command from the project directory:
-
-	./template examples/vars examples/text.tpl
-
 ## Specification
 
 This section describes the behavior of the program in excruciating detail and
@@ -80,7 +85,7 @@ expression metacharacters:
     \ ^ $ . [ ] | ( ) * + ? { }
 
 There is one exception to this rule: Variable values may reference variables
-defined earlier in the file, in which case they must use the brace- delimited
+defined earlier in the file, in which case they must use the brace-delimited
 variable format described above. Any other use of braces or any other
 prohibited character remains illegal when referencing a previously defined
 variable. The specified variable name must reference an actual variable
diff --git a/example/text.tpl b/example/text.tpl
index 4b6b5a4..06adb72 100644
--- a/example/text.tpl
+++ b/example/text.tpl
@@ -1,3 +1,5 @@
-The numbers before 3 are {{ one }} and {{two}}. The first number is {{ one }}.
+My favorite food is {{ food }}, and my favorite beverage is {{ beverage }}.
+I'm going to have {{ dinner }} for dinner tonight.
 
-My favorite color is {{ favorite_color }}. My car is {{ car_color }}.
+The first three numbers are {{one}}, {{two}}, and {{three}}. {{one}} is the
+smallest of the three.
diff --git a/example/vars b/example/vars
index b8182ba..32d59d2 100644
--- a/example/vars
+++ b/example/vars
@@ -1,5 +1,12 @@
 # This is a comment.
+food = pizza
+beverage = coffee
+
+# Previously defined variables can be used in variable definitions.
+# Whitespace is optional inside braces.
+dinner = {{ food }} and {{beverage}}
+
+# The = character can be surrounded by any number of whitespace characters.
 one	= 1
 two	= 2
-favorite_color=bluish gray
-car_color = {{ favorite_color }}
+three=3
diff --git a/template b/template
index ef1a72e..54f0f6a 100755
--- a/template
+++ b/template
@@ -4,15 +4,18 @@ BEGIN { FS = "[[:space:]]*=[[:space:]]*" }
 
 FILENAME == ARGV[1] && /^#/ { next }
 FILENAME == ARGV[1] && NF == 2 {
-	# If the value is a template variable that matches a previously defined
-	# variable, use that variable's value. Otherwise, use the literal
-	# value.
-	if (match($2, /\{\{[[:space:]]*[^\{\}[:space:]]+[[:space:]]\}\}/)) {
-		match($2, /[^\{\}[:space:]]+/)
-		vals[$1] = vals[substr($2, RSTART, RLENGTH)]
-	} else {
-		vals[$1] = $2
+	# Replace template variables with previously defined values.
+	while (match($2, /\{\{[[:space:]]*[^\{\}[:space:]]+[[:space:]]\}\}/)) {
+		matched_text = substr($2, RSTART, RLENGTH)
+
+		# Extract the actual var name, without braces and space.
+		match(matched_text, /[^\{\}[:space:]]+/)
+		var_name = substr(matched_text, RSTART, RLENGTH)
+
+		sub(matched_text, vals[var_name], $2)
 	}
+
+	vals[$1] = $2
 }
 FILENAME == ARGV[1] { next }