“if -e”和“if -f”之间的区别

Question

There are two switches for the if condition which check for a file: -e and -f .

What is the difference between those two?

Answer 1

See: http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html

I believe those aren't "if switches", rather "test switches" (because you have to use them inside [] brackets.

But the difference is:

[ -e FILE ] True if FILE exists.

This will return true for both /etc/hosts and /dev/null and for directories.

[ -f FILE ] True if FILE exists and is a regular file. This will return true for /etc/hosts and false for /dev/null (because it is not a regular file), and false for /dev since it is a directory.

Answer 2

$ man bash

       -e file
              True if file exists.
       -f file
              True if file exists and is a regular file.

A regular file is something that isn't a directory, symlink, socket, device, etc.

Answer 3

-e checks for any type of filesystem object; -f only checks for a regular file.

Answer 4

The if statement actually uses the program 'test' for the tests. You could write if statements two ways:

if [ -e filename ];

or

if test -e filename;

If you know this, you can easily check the man page for 'test' to find out the meanings of the different tests:

man test