Shell (2) condition 2.16.doc

Used
If/while
And so on;

 

Test
Command

Test Condition
, When the condition is
True
Returns
0
;

If
Test condition; then
If
[Condition]; then
#

Note the space,
TBD

Supported?
If 0

...
<=>
...

Fi
Fi

 

Test
Condition judgment, three types

1

) Value Comparison

-Eq-ge-GT-le-lt-ne

 

2

) String comparison:

=
! =
<> (
Note escape
)-N (
Non-empty string
)-Z (
Empty string or not
)
;

Test
Uppercase and lowercase letters are the same
Sort
Opposite

 

Eg: If ["A"/> "B"]; then

Eg: If [-n "$1"]; then
<=> ["$1"]
#$1
It must be caused. Otherwise, it will fail to be judged.

Eg: If [string1-A string2]; then
# String1/string2
True

Eg: If [string1-O string2]; then # string1
Or
String2
True

 

3

) File comparison:

-D File
# Directory,
File
Is it a directory?

-E
# Exist,
File
Exist?

-F
# File
,
An exist File

-R
# Readable

-S
# Not
Empty

-W
# Writable

-X
# Executable
, And
Current User
You must have the execution permission.

-O
# Owered
By current user

-G
#
The default file user group is
Current User Group

File1-nt file2
# File1 new than file2

File1-ot file2
# Old

The above comparison will return a failure if the file does not exist. Therefore, you can determine whether the file exists before executing other comparisons;

 

Composite condition comparison

Similar
C
:
[Cond1] & [cond2] | [
Cond3]

 

If [
'A'/<'B'] & ['A'/<"C"] | ['A'/<'A'
]; Then

 

Advanced features:

A mathematical expression in a double parentheses table. It can also be used for mathematical computation,
If ($ A ** 2> 90 ))

The regular expression can be used to provide the pattern matching function,
If [[$ A = r *]

 

TBD
: How does one express non-logical?