file test operators in bash

Often while writing shell scripts, various tests need to be performed on files. For example, we need to check if a file exists before copying it somewhere. We need to check the existence of a directory before writing files into it.

Bash comes with the following list of operators to perform these tests.

Operator    Tests Whether
-e          File exists
-f          File is a regular file
-d          File is a directory
-h          File is a symbolic link
-L          File is a symbolic link
-b          File is a block device
-c          File is a character device
-p          File is a pipe
-S          File is a socket
-t          File is associated with a terminal

-N          File was modified since last read
-O          You own the file
-G          Group id of the file is same as yours

-s          File is not zero size

-r          File has read permission
-w          File has write permission
-x          File has execute permission

-g          sgid flag set
-u          suid flag set
-k          "sticky bit" set

F1 -nt F2   File F1 is newer than F2 *
F1 -ot F2   File F1 is older than F2 *
F1 -ef F2   Files F1 and F2 are hard links to the same file *


!           NOT (inverts the sense of above tests)

* signifies a binary operator (requires two operands).

Reference :- Appendix B of "Advanced Bash-Scripting guide" by Mendel Cooper, Version 6.5. Debian users can get this document by installing the abs-guide package.

sudo apt-get install abs-guide

The necessary files can be found in /usr/share/doc/abs-guide . However, the abs-guide package contains only the html version of the document. A pdf version can be downloaded from http://www.tldp.org/LDP/abs/abs-guide.pdf .