Skip to content

variable+x

By claude-3-5-sonnet 2024-11-12 11:04:32 +11:00 Tue

Let's break down how [ -n "${MODEL_SIZES[$model_name]+x}" ] works:

  1. ${MODEL_SIZES[$model_name]} - This tries to access the array value for key $model_name

  2. ${variable+x} is a special parameter expansion in bash that:

  3. Returns x if the variable exists (even if empty)

  4. Returns nothing if the variable doesn't exist

  5. So ${MODEL_SIZES[$model_name]+x} means:

  6. If the array has the key $model_name: returns "x"

  7. If the array doesn't have the key: returns empty string

  8. [ -n STRING ] tests if STRING is non-empty

  9. Returns true (0) if STRING is non-empty
  10. Returns false (1) if STRING is empty

Putting it all together: 

# If "tiny.en" exists in MODEL_SIZES:
model_name="tiny.en"
[ -n "${MODEL_SIZES[$model_name]+x}" ]  # Returns true

# If "invalid" doesn't exist in MODEL_SIZES:
model_name="invalid"
[ -n "${MODEL_SIZES[$model_name]+x}" ]  # Returns false

Example with debug output: 

# With valid model
model_name="tiny.en"
echo "${MODEL_SIZES[$model_name]+x}"  # Prints: x
[ -n "${MODEL_SIZES[$model_name]+x}" ] && echo "exists" || echo "doesn't exist"
# Prints: exists

# With invalid model
model_name="invalid"
echo "${MODEL_SIZES[$model_name]+x}"  # Prints: (empty)
[ -n "${MODEL_SIZES[$model_name]+x}" ] && echo "exists" || echo "doesn't exist"
# Prints: doesn't exist

This is more reliable than pattern matching because it: 1. Uses bash's built-in array key checking 2. Avoids issues with special characters in names 3. Is more efficient than looping or string matching 4. Has clearer intent - explicitly checking if key exists