The code snippet `if [ -n "$MATCHING_TOPICS" ]; then` is...

The code snippet if [ -n "$MATCHING_TOPICS" ]; then is a Bash scripting statement that checks a specific condition. Here's a breakdown of what it does:

1. Condition: [ -n "$MATCHING_TOPICS" ]

   • -n is a test operator that evaluates "if the string is not empty".
   • "$MATCHING_TOPICS" is a variable that is being checked. Double quotes are used to ensure proper handling, especially if the variable is empty or contains spaces.

2. What it checks:

   • If the variable MATCHING_TOPICS contains a non-empty string, the condition evaluates as true.
   • If MATCHING_TOPICS is empty or unset, the condition evaluates as false.

3. What happens next:

   • If the condition is true (i.e., MATCHING_TOPICS is not empty), the code block following then is executed.
   • If the condition is false (i.e., MATCHING_TOPICS is empty or unset), the code block inside the else (if any) or no block (if no else is defined) is executed.

Example:

MATCHING_TOPICS="hello"

if [ -n "$MATCHING_TOPICS" ]; then
  echo "The variable MATCHING_TOPICS is not empty."
else
  echo "The variable MATCHING_TOPICS is empty."
fi

• If MATCHING_TOPICS="hello", it prints: The variable MATCHING_TOPICS is not empty.
• If MATCHING_TOPICS="" or is unset, it prints: The variable MATCHING_TOPICS is empty.

Summary:

The code checks whether the variable MATCHING_TOPICS is not empty and executes the subsequent block of code if that is true.