Logical judgment in 20.5shell scripts 20.6 file directory attribute Judge 20.7-9if Special usage case judgment

Logic Judgments in 20.5shell scripts


Format 1:if condition; Then statement; Fi
Most of the time it's used in this format


Format 2:if condition; Then statement; else statement; Fi


Format 2:if condition; Then statement; else statement; Fi

20.6 File Directory property judgment

[-F file] Determines if it is a normal file, and there is

Execution process

The above does not exist already created, and executing again already exists

[-D file] Determines if it is a directory and exists

-D to see if it is a directory, not just create

-E To see if there is

In the shell, touch is able to create directories and files, and if a directory or file already exists, it will change its 3 time

Whether it is readable

is executable

Front Plus! is to take the inverse [-f $f] | | [Touch $f = if [-f $f] then touch $f fi
|| Indicates that the following command is executed when the previous condition does not exist
&& indicates that the following command is executed when the previous condition exists

20.7 If special usage

If [-Z ' $a '] This indicates what happens when the value of variable A is empty

When it has no value, it will get an error.

The-Z representation is empty, and its usage


Exit exits when the previous conditions are met

Use of-N
Output when $b is not empty $b when null output B is null
The file is not enclosed in double quotes, and the variable is enclosed in double quotes.

-Q is not displaying filtered content-W more precise specified single character

20.8/20.9 Case Judgment

Vi/etc/init.d/network, there's a case statement.
#!/bin/bash
Read-p "Please input a number:" N
If [-Z "$n"]
Then
echo "Please input a number."
Exit 1
Fi
n1=echo $n|sed ‘s/[0-9]//g‘
If [-N "$n 1"]
Then
echo "Please input a number."
Exit 1
Fi
If [$n-lt] && [$n-ge 0]
Then
Tag=1
elif [$n-ge] && [$n-LT 80]
Then
tag=2
elif [$n-ge] && [$n-LT 90]
Then
Tag=3
elif [$n-ge] && [$n-le 100]
Then
Tag=4
Else
Tag=0
Fi
Case $tag in
1)
echo "Not OK"
;;
2)
echo "OK"
;;
3)
echo "Ook"
;;
4)
echo "Oook"
;;
*)
echo "The number range is 0-100."
;;
Esac


Read-p "Please input a number:" N read-p is the function of the previous assignment, n is how much

Execute the script, enter the number 101, and view the results of the execution

Logical judgment in 20.5shell scripts 20.6 file directory attribute Judge 20.7-9if Special usage case judgment