Using file attributes with conditional logic

Earlier in this book, we touched upon various tests for strings, numbers, and variables. Using a similar concept built into Bash, we can also use various attributes to test against files and directories. This extends upon the introduction conditional logic to perform tests on files. Does an example exist? Is it a directory? and so on.

For a moment, though, couldn't we just use the results from executing and checking the return code? Absolutely! This is another method you can use, especially if you are using a version of Bash that supports all of Bashes features. It is just another way to "skin the rabbit".

Let's start off first with some of the common flags, which return true if:

• -e: The file exists
• -f: This is a regular file and not a directory or device file
• -s: The file is not empty or zero in size
• -d: This is a directory
• -r: This has read permissions
• -w: This has write permissions
• -x:This has execute permissions
• -O: This is the owner of the file the current user
• -G: This executes the user if they have the same group as yours
• f1 (- nt, -ot, -ef) f2: Refers to if f1 is newer than f2, older than f2, or are hard-linked to the same file