What is the definition file in Linux? The file is almost everything - keyboard, and disk, and the regular file. Here is example of regular file: document.odt or /etc/passwd.
If you want the script to find out if there is any file (eg. tile.txt or /dev/sda), you can do the following:
if [ -e /root/file.txt ]; then echo "File found"; fi
So, we tested if any kind of file (named /root/file.txt) exists.
If you want to take into consideration just regular files (not /dev/sda but just /root/file.txt), you can use -f parameter instead of -e parameter:
if [ -f /root/file.txt ]; then echo "Regular file found"; fi
If you want to check, if regular file not exists, you can use not(!) in test command :
if [ ! -f /root/file.txt ]; then echo "Regular file not found"; fi
We could to tune last example. You can also use short way how to write it:
[ ! -f /root/file.txt ] && echo "Regular file not found"
It is my favorite, if you have just one command after test command.
Here are some examples of file test operators:
|-s||File is a regular file (if file is directory or device returns false)|
|-d||File is a directory|
|-b||File is a block device|
|-c||File is a character device|
|-p||File is a pipe|
|-w||File has a write permission|
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