Shell file expression

file Expression

-e filename true if filename exists
-d filename If filename is a directory, true
-F filename True if filename is a regular file
-L filename True if filename is a symbolic link

-r filename If filename is readable, true
-W filename if filename is writable, true
-x filename If filename is executable, true
-S filename true if the length of the file is not 0
-H filename True if the file is a soft link
Filename1-nt filename2 If filename1 is newer than filename2, it is true.
Filename1-ot filename2 If filename1 is older than filename2, it is true.

An integer variable expression
-eq equals
-ne Not equal to
-GT Greater than
-ge greater than or equal to
-lt less than
-le less than or equal to

string-Variable expression

if [$a = $b] true if string1 equals string2
string allows an equal sign with an assignment number
if [$string 1! = $string 2] True if string1 is not equal to string2
If [-n $string] returns 0 (true) if string is non-null (not 0)
If [-Z $string] True if string is empty
If [$sting] if string is not NULL, return 0 (and-n similar)

Logical Non! The opposite of the conditional expression

if [! expression]
if [!-D $num] If there is no directory $num

逻辑与 –a                   条件表达式的并列

If [expression 1–a-expression 2]

逻辑或 -o                   条件表达式的或

If [expression 1–o-expression 2]

Shell file expression