Bash stuff: parameter substitution, expansion and manipulation operators; file test operators

file_test.md

Test	Description
-e	file exists
-f	file is a regular file (not a directory or device file)
-s	file is not zero size
-d	file is a directory
-b	file is a block device
-c	file is a character device
-p	file is a pipe
-L	file is a symbolic link
-S	file is a socket
-t	file (descriptor) is associated with a terminal device (stdin, stdout,...)
-r	file has read permission (for the user running the test)
-w	file has write permission (for the user running the test)
-x	file has execute permission (for the user running the test)
-g	set-group-id (sgid) flag set on file or directory
-u	set-user-id (suid) flag set on file
-k	sticky bit set
-O	you are owner of file
-G	group-id of file same as yours
-N	file modified since it was last read
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" -- reverses the sense of the tests above (returns true if condition absent)

variable_manipulation.md

Command	Description
${parameter:-defaultValue}	Get default shell variables value
${parameter:=defaultValue}	Set default shell variables value
${parameter:?"Error Message"}	Display an error message if parameter is not set
${#var}	Find the length of the string
${var:offset:length}	Substring
${var%pattern}	Remove from shortest rear (end) pattern
${var%%pattern}	Remove from longest rear (end) pattern
${var#pattern}	Remove from shortest front pattern
${var##pattern}	Remove from longest front pattern
${var/pattern/string}	Find and replace (only replace first occurrence)
${var//pattern/string}	Find and replace all occurrences