Shell basics 1

The first shell script program. VI create a file test. SH and grant the execution permission

 

#!/bin/shecho 'hello word !'

 

Execution result: Hello word!

Shell script structure #! Start with/bin/sh, and next to the line feed is the program body. Of course, here we only use #! /Bin/sh is used as an example.

I generally follow this process to learn a new language.

1. assign values to variables and variables

2. Process Control

3. dataset operation: Set Array

4. Class and method call

I am familiar with the above things and have the most basic knowledge of this language.

I. Variables

All variables are strings and do not need to be declared.

first='OKOKOK'

Note that there is no space between the left and right sides of the equal sign.

Reference: $ {First} or $ {First}

# Assign the first value to secondsecond = $ first

 

 

first=2echo 'this is ${first}'

Execution result: This is 2

 

2. Process Control

1. If judgment

if...then.....elif....then.....else....fi

Format.

Different from Java, Java conditions are wrapped with (), and shell conditions are enclosed with [] or () square brackets. Note that there must be spaces before and after square brackets.

For example:

a='1'if [ ${a} -eq '1' ]then echo 'this is 1'elif [ ${a} -eq '2' ]then echo 'this is 2'else echo 'this is other'fi

 

Execution result: This is 1

The above program compares whether a variable is equal to a value.

 

The following is the if judgment of the composite condition.

a='3'if [[ ${a} -eq '1' ]] || [[  ${a} -eq '3' ]]then echo 'this is 1'elif [ ${a} -eq '2' ]then echo 'this is 2'else echo 'this is other'fi

Execution result: this is 1

In java, if (a. equals ("1") | a. equals ("3"), but not here.

This is also possible:

if [ ${a} -eq '1' -o   ${a} -eq '3' ]

-O: Yes |, or

When it comes to process judgment, expressions and logical operators are required. The next article will write the corresponding information.