How to Check File Non-Existence in Bash

To check if a file does not exist in Bash scripting, you need to use the ! (NOT) operator to negate the file existence test. Instead of [ -f $FILE ], you should use [ ! -f $FILE ] to specifically check for non-existence.

Contents

• Basic File Non-Existence Check
• Different Methods for Checking File Non-Existence
• Using Logical Operators with File Checks
• Best Practices and Common Pitfalls
• Practical Examples and Use Cases
• Advanced File Type Checks

Basic File Non-Existence Check

The most straightforward way to check if a file does not exist is to use the ! operator with the -f test. In your current code, you already have the logic for both existence and non-existence, but if you want to specifically check for non-existence, here’s how to modify it:

#!/bin/bash

FILE=$1
if [ ! -f "$FILE" ]; then
   echo "File $FILE does not exist."
else
   echo "File $FILE exists."
fi

The key change is adding the ! operator before -f "$FILE". This negates the condition, so the if block now executes when the file does not exist.

According to the official test documentation, “To check whether a file does not exist, use the NOT (!) operator and negate the condition by employing the if ! test OPERATOR FILE_NAME syntax.”

Different Methods for Checking File Non-Existence

There are several ways to check if a file does not exist in Bash:

1. Using the test Command with [ ]

if [ ! -f "$FILE" ]; then
    echo "File does not exist"
fi

2. Using the test Command Directly

if ! test -f "$FILE"; then
    echo "File does not exist"
fi

3. Using the Modern [[ ] Syntax

if [[ ! -f "$FILE" ]]; then
    echo "File does not exist"
fi

As explained by LinuxSimply, the single square brackets [ ] is treated as the equivalent syntax to the test command, while the double square brackets [[ ]] provide more advanced features.

The differences between these methods are subtle, but [[ ]] is generally recommended for modern Bash scripting as it provides better error handling and additional features.

Using Logical Operators with File Checks

You can also combine file existence checks with logical operators for more complex conditions:

Using && (AND) Operator

[ ! -f "$FILE" ] && echo "File does not exist"

This executes the echo command only if the file does not exist.

Using || (OR) Operator

[ ! -f "$FILE" ] || echo "File exists"

This executes the echo command only if the file exists (because the condition is negated).

Combined Operations

[ ! -f "$FILE" ] && echo "File missing, creating..." && touch "$FILE"

As nixCraft demonstrates, you can chain multiple commands together using the && operator.

Best Practices and Common Pitfalls

Always Quote Variables

# Good
if [ ! -f "$FILE" ]; then

# Bad (can fail with filenames containing spaces)
if [ ! -f $FILE ]; then

Use Full Paths When Possible

# More reliable
if [ ! -f "/path/to/$FILE" ]; then

Handle Multiple File Types

# Check for any file (including directories)
if [ ! -e "$FILE" ]; then

# Specifically check for regular files only
if [ ! -f "$FILE" ]; then

According to Stack Overflow, “The relevant man page is man test or, equivalently, man [ – or help test or help [ for the built-in bash command.”

Practical Examples and Use Cases

Example 1: Creating a File If It Doesn’t Exist

#!/bin/bash

CONFIG_FILE="/etc/myapp/config.conf"

if [ ! -f "$CONFIG_FILE" ]; then
    echo "Creating default configuration file..."
    mkdir -p "$(dirname "$CONFIG_FILE")"
    cat > "$CONFIG_FILE" << EOF
# Default configuration
setting1=value1
setting2=value2
EOF
    echo "Configuration file created successfully."
else
    echo "Configuration file already exists."
fi

Example 2: Backup Script with File Existence Check

#!/bin/bash

SOURCE_FILE="$1"
BACKUP_DIR="/backups"
TIMESTAMP=$(date +%Y%m%d_%H%M%S)
BACKUP_FILE="$BACKUP_DIR/$(basename "$SOURCE_FILE")_$TIMESTAMP"

if [ ! -f "$SOURCE_FILE" ]; then
    echo "Error: Source file '$SOURCE_FILE' does not exist."
    exit 1
fi

if [ ! -d "$BACKUP_DIR" ]; then
    echo "Creating backup directory..."
    mkdir -p "$BACKUP_DIR"
fi

cp "$SOURCE_FILE" "$BACKUP_FILE"
echo "Backup created: $BACKUP_FILE"

Example 3: Conditional Script Execution

#!/bin/bash

LOCK_FILE="/tmp/myapp.lock"

if [ ! -f "$LOCK_FILE" ]; then
    echo "Starting application..."
    # Application logic here
    touch "$LOCK_FILE"
    # ... application code ...
    rm "$LOCK_FILE"
else
    echo "Application is already running (lock file exists)."
    exit 1
fi

As Zero To Mastery explains, “In this example, we’re using the ! -e condition to check if the file doesnt exist.”

Advanced File Type Checks

Besides regular files, you can check for other types of non-existent files:

For example, to check if a directory doesn’t exist before creating it:

if [ ! -d "/path/to/directory" ]; then
    mkdir -p "/path/to/directory"
    echo "Directory created"
fi

Sources

1. How do I tell if a file does not exist in Bash? - Stack Overflow
2. 6 Ways to Check If a File Exists or Not in Bash - LinuxSimply
3. How to check if file does not exist in Bash - nixCraft
4. How To Check If A File Exists in Bash (With Code Examples) | Zero To Mastery
5. How to Check if a File Exists in Linux Bash Shell - nixCraft

Conclusion

• The proper way to check if a file does not exist in Bash is using the ! operator: [ ! -f "$FILE" ]
• Always quote your file variables to handle filenames with spaces correctly
• Consider using [[ ]] instead of [ ] for more robust error handling in modern Bash scripts
• You can combine file checks with logical operators (&&, ||) for more concise code
• Different test operators (-f, -d, -e, etc.) allow you to check for specific types of non-existent filesystem objects
• File existence checks are essential for creating robust scripts that handle missing dependencies gracefully

By mastering these file existence check techniques, you’ll be able to write more reliable and professional Bash scripts that gracefully handle various filesystem scenarios.