How do I tell if a file does not exist in Bash?

To check if a file does not exist in Bash, use the test command ([ ]) with the -f (file) or -e (file/directory) flag and the negation operator !. Here’s how to do it:

Basic Syntax

if [ ! -f "$file" ]; then
  echo "File $file does NOT exist"
fi

or for any file type (including directories/symlinks):

if [ ! -e "$file" ]; then
  echo "File/directory $file does NOT exist"
fi

Key Options

Flag	Purpose
-f	Check if a regular file exists
-e	Check if any file/directory exists
!	Negate the condition (true if file missing)

Examples

1. Check if a file is missing and act:

file="/path/to/your/file.txt"

if [ ! -f "$file" ]; then
  echo "Error: $file not found. Creating it..."
  touch "$file"
fi

2. Fail a script if a required file is missing:

config="config.yaml"
if [ ! -f "$config" ]; then
  echo "Critical: $config missing. Exiting."
  exit 1
fi

3. Check for multiple files:

if [ ! -f "$file1" ] && [ ! -f "$file2" ]; then
  echo "Neither $file1 nor $file2 exists."
fi

Using [[ ]] for Advanced Checks

The [[ ]] construct (Bash-only) is safer for variables with spaces or special characters:

if [[ ! -f $file ]]; then  # Quotes optional inside [[ ]]
  echo "$file not found"
fi

Common Pitfalls

1. Spacing: Ensure spaces inside [ ] or [[ ]]:

   [ ! -f "$file" ]  # ✅ Correct
   [! -f "$file" ]   # ❌ Fails (no space after [)

2. Quoting Variables: Always quote "$file" to handle filenames with spaces:

   [ ! -f "$file" ]  # ✅ Safe for "my file.txt"
   [ ! -f $file ]    # ❌ Breaks on spaces

3. Symlinks: Use -e instead of -f if checking for symlink existence.

Summary

• Use [ ! -f "$file" ] for regular files.
• Use [ ! -e "$file" ] for any file/directory.
• Prefer [[ ]] in Bash scripts for better readability and safety.