More and more when I need to automate backup tasks or perform devops tasks, it becomes essential for me to verify the existence or not of specific files or directories. In Bash, you can use the TEST command to check whether a file exists and determine the type of the file.

The test command takes one of the following syntax forms:

test EXPRESSION

[ EXPRESSION ]

[[ EXPRESSION ]]

If you want your script to be portable, you should prefer using the old test [ command, which is available on all POSIX shells. The new upgraded version of the test command [[ (double brackets) is supported on most modern systems using Bash, Zsh, and Ksh as a default shell.

Check if File exists

When we want to check if a file exists, the most used FILE operators are -e and -f. The first -e we will use to check if a file exists regardless of type. Now if we want to check that a file is a specification, not a directory or a device, use the second -f .

The most common option to check whether a file exists or not is to use the TEST command in combination with the if statement. Let’s say we want to check if there is a backup file from the previous day before executing an action:

Option using TEST

FILE=/backup_dir/file_$(date -d yesterday +%Y_%m_%d)
if test -f "$FILE"; then
    echo "$FILE exists."
fi

Option using [ ]

FILE=/backup_dir/file_$(date -d yesterday +%Y_%m_%d)
if [ -f "$FILE" ]; then
    echo "$FILE exists."
fi

Option using [[ ]]

FILE=/backup_dir/file_$(date -d yesterday +%Y_%m_%d)
if [[ -f "$FILE" ]]; then
    echo "$FILE exists."
fi

If our intention is to perform different actions depending on whether or not the file exists, we can make use of THEN and ELSE

FILE=/backup_dir/file_$(date -d yesterday +%Y_%m_%d)
if [ -f "$FILE" ]; then
    echo "$FILE exists."
else 
    echo "$FILE does not exist."
fi

Check if Directory exist

The operators -d allows you to check if a directory exist or not.

For example to check whether the /backup_dir directory exist you would use:

FILE=/backup_dir/
if [ -d "$FILE" ]; then
    echo "$FILE is a directory."
fi

You can also use the double brackets [[ ]] instead of a single one [ ].

Check if File or Directory does not exist

Using the exclamation mark !, as in most programming languages, we can negate an expression.

Check if File does not exist

FILE=/backup_dir/file_$(date -d yesterday +%Y_%m_%d)
if [ ! -f "$FILE" ]; then
    echo "$FILE does not exist."
fi

Check if Directory does not exist

FILE=/backup_dir/
if [ ! -d "$FILE" ]; then
    echo "$FILE does not exist."
fi

Concluding

This guide, like most of the posts on this blog, are the result of questions that I have had while developing some tasks in my daily work. I hope this solution will simplify other people’s work.
If you have any questions or suggestions, you can leave a comment.