Linux shell basic Grammar Amur2
Amur1 talked about some basic grammar, and A2 continues what it said last time.
Shell is a programming language, and naturally there are structured representations. The common programming language structure is judgment and loop. The judgment in shell can be divided into three categories: numerical judgment, character judgment and file judgment.
Several forms of judgment
If command
Then
Command
FiIf command
Then
Command
Else
Command
Fi
If command
Then
Command
Elif command
Then
Command
Else
Command
Fi
(1) numerical judgment
Example: simple guessing of numbers
(2) character judgment
Example: determine the input option
(3) document judgment
Example: check whether the destination path exists before creating the log file
#! / bin/bash
If [!-d / mnt/123testlog/2019-08-31]
Then
Mkdir-p / mnt/123testlog/2019-09-31
Fi
Still need to pay attention to
The usage of If test xxxx
The parameters are worth judging and dealing with.
Compound condition judgment
If [] & & []
If [] | | []
Double parentheses
-- double parentheses (advanced features of mathematical expressions)
-- double parentheses (string advanced features)
It is more complicated to use if structure in multi-choice judgment, and it is better to use case.
Case
Case xxx in
P1)
Cmd
P2)
Cmd
*)
Default cmd
Esac
You can use case when dealing with the input parameters of the script, and then shift the parameters
Input can also be processed as follows, and the usage of getopt and getopts will be described in more detail later.
Getopt
Getopts
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