If

If File

Check if File Exists

Bash

FILE=/some/file.conf
if test -f "$FILE"; then
    echo "$FILE exists."
fi

Bash

FILE=/some/file.conf
if [[ -f "$FILE" ]]; then
    echo "$FILE exists."
fi

Bash

FILE=/some/file.conf
if [ -f "$FILE" ]; then
    echo "$FILE exists."
else
    echo "$FILE does not exist."
fi

Check if File does Not Exist

Bash

FILE=/etc/docker
if [ ! -f "$FILE" ]; then
    echo "$FILE does not exist."
fi

Check if Multiple Files Exist

Bash

if [ -f /etc/resolv.conf -a -f /etc/hosts ]; then
    echo "Both files exist."
fi

Bash

if [[ -f /etc/resolv.conf && -f /etc/hosts ]]; then
    echo "Both files exist."
fi

Check if Directory Exist

Bash

DIR=/some/dir
if [ -d "$DIR" ]; then
    echo "$DIR is a directory."
fi

File test operators

-b FILE - True if the FILE exists and is a special block file.
-c FILE - True if the FILE exists and is a special character file.
-d FILE - True if the FILE exists and is a directory.
-e FILE - True if the FILE exists and is a file, regardless of type (node, directory, socket, etc.).
-f FILE - True if the FILE exists and is a regular file (not a directory or device).
-G FILE - True if the FILE exists and has the same group as the user running the command.
-h FILE - True if the FILE exists and is a symbolic link.
-g FILE - True if the FILE exists and has set-group-id (sgid) flag set.
-k FILE - True if the FILE exists and has a sticky bit flag set.
-L FILE - True if the FILE exists and is a symbolic link.
-O FILE - True if the FILE exists and is owned by the user running the command.
-p FILE - True if the FILE exists and is a pipe.
-r FILE - True if the FILE exists and is readable.
-S FILE - True if the FILE exists and is a socket.
-s FILE - True if the FILE exists and has nonzero size.
-u FILE - True if the FILE exists, and set-user-id (suid) flag is set.
-w FILE - True if the FILE exists and is writable.
-x FILE - True if the FILE exists and is executable.