Short Notes on Bash

Extensions and File Name

$ fullname='/tmp/file.tar.gz'
$ filename=$(basename $fullname)
$ echo ${filename##*.}
>> gz
$ echo ${filename#*.}
>> tar.gz
$ echo ${filename%.*}
>> file.tar
$ echo ${filename%%.*}
>> file

For more options and explanations, see Bash - Shell Parameters Expansion.

File Test Operators

Operator	Function
-e	file exists
-f	exists and is regular file (not directory or device file)
-s	exists and is non-zero size
-d	exists and is directory
-b	exists and is block device
-c	exists and is character device
-p	exists and is pipe
-h	exists and is symbolic link
-S	exists and is socket
-t	is associated with terminal device; e.g. [ -t 0 ] and [ -t 1 ] test whether stdin and stdout is terminal
-r	user has read permission
-w	user has write permission
-x	user has execute permission
-O	user is owner
-G	user's group is the same as the file's group
-N	file modified since it was last read
f1 -nt f2	f1 is newer than f2
f1 -ot f2	f1 is older than f2