File Comparisons

-d	Checks if file exists and is a directory	`if [ -d $file ] then do_something fi`
-e	Checks if file exists	`if [ -e $file ] then do_something fi`
-f	Checks if file exists and is a file	`if [ -f $file ] then do_something fi`
-r	Checks if file exists and is readable	`if [ -r $file ] then do_something fi`
-s	Checks if file exists and is not empty	`if [ -s $file ] then do_something fi`
-w	Checks if file exists and is writable	`if [ -w $file ] then do_something fi`
-x	Checks if file exists and is executable	`if [ -x $file ] then do_something fi`
-O	Checks if file exists and is owned by the current user	`if [ -O $file ] then do_something fi`
-G	Checks if file exists and the default group is the same as the current user	`if [ -G $file ] then do_something fi`
file1 -nt file2	Checks if file1 is newer than file2	`if [ $file1 -nt $file2 ] then do_something fi`
file1 -ot file2	Checks if file1 is older than file2	`if [ $file1 -ot $file2 ] then do_something fi`