Comments in HCL in Terraform - Step-by-Step Execution

Process Flow - Comments in HCL

Start reading HCL file

↓

Encounter # or //?

Yes→Ignore rest of line

No↓

Encounter /*?

Yes→Ignore until */ found

No↓

Process code normally

↓

End of file

Terraform reads the file line by line, ignoring text after # or // on a line, or between /* and */ for block comments, then processes the rest as code.

Execution Sample

Terraform

# This is a comment
resource "aws_s3_bucket" "b" {
  // Another comment
  bucket = "mybucket"
  /* Block comment
     spanning lines */
  acl = "private"
}

This HCL snippet shows single-line comments with # and //, and a multi-line block comment with /* */ inside a resource block.

Process Table

Step	Line Read	Comment Detected	Action	Code Processed
1	# This is a comment	Yes (#)	Ignore entire line
2	resource "aws_s3_bucket" "b" {	No	Process line as code	resource "aws_s3_bucket" "b" {
3	// Another comment	Yes (//)	Ignore entire line
4	bucket = "mybucket"	No	Process line as code	bucket = "mybucket"
5	/* Block comment	Yes (/*)	Start ignoring until */
6	spanning lines */	Inside block comment	End ignoring at */
7	acl = "private"	No	Process line as code	acl = "private"
8	}	No	Process line as code	}
9	End of file	No	Stop processing

💡 Reached end of file, all comments ignored properly, code lines processed.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5-6	After Step 7	After Step 8	Final
Processed Code Lines	[]	[]	["resource \"aws_s3_bucket\" \"b\" {"]	["resource \"aws_s3_bucket\" \"b\" {"]	["resource \"aws_s3_bucket\" \"b\" {", "bucket = \"mybucket\""]	["resource \"aws_s3_bucket\" \"b\" {", "bucket = \"mybucket\""]	["resource \"aws_s3_bucket\" \"b\" {", "bucket = \"mybucket\"", "acl = \"private\""]	["resource \"aws_s3_bucket\" \"b\" {", "bucket = \"mybucket\"", "acl = \"private\"", "}"]	["resource \"aws_s3_bucket\" \"b\" {", "bucket = \"mybucket\"", "acl = \"private\"", "}"]

Key Moments - 3 Insights

Why does the line starting with # get ignored completely?

Because lines starting with # are single-line comments, Terraform ignores everything after # on that line as shown in execution_table step 1.

How does Terraform handle multi-line comments with /* and */?

Terraform ignores all text starting from /* until it finds */, skipping all lines in between, as shown in steps 5 and 6 in the execution_table.

What happens to lines with // comments?

Lines starting with // are treated as single-line comments and ignored entirely, like in step 3 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 4. What code line is processed?

A bucket = "mybucket"

B // Another comment

C # This is a comment

D acl = "private"

💡 Hint

Check the 'Code Processed' column at step 4 in the execution_table.

At which steps does Terraform ignore lines due to block comments?

A Steps 1 and 3

B Steps 2 and 4

C Steps 5 and 6

D Steps 7 and 8

💡 Hint

Look for 'Start ignoring until */' and 'Inside block comment' in the 'Comment Detected' column.

If the line with // comment was changed to a code line, how would the 'Processed Code Lines' change after step 3?

A It would still ignore the line

B It would include the new code line after step 3

C It would cause an error

D It would be treated as a block comment

💡 Hint

Refer to variable_tracker 'Processed Code Lines' after step 3 and how comments affect processing.

Concept Snapshot

Comments in HCL:
- Use # or // for single-line comments
- Use /* ... */ for multi-line block comments
- Terraform ignores comments during parsing
- Comments can be placed anywhere outside strings
- Properly ignoring comments keeps code clean and readable

Full Transcript

Terraform configuration files use comments to add notes or explanations without affecting the code. Single-line comments start with # or // and ignore the rest of that line. Multi-line comments start with /* and end with */ and can span multiple lines. When Terraform reads the file, it skips these comments and processes only the actual code lines. This helps keep configurations clear and maintainable.