Getting started with shell variables

1 Custom global variables

2.1 Father and son Shell Introduction to the environment

for example : Yes 2 individual Shell Script files parent.sh and child.sh

If stay parent.sh In the script file child.sh Script files , that parent.sh Is the father Shell Environmental Science , child.sh It's the son Shell Environmental Science

2.2 Introduction to custom global variables

Is to define global variables in the current script file , This global variable can be used in the current Shell Environment and sub Shell It can be used in the environment

2.3 Custom global variable Syntax

export var_name1 var_name2

2.4 DEMO

Test the global variable in the child Shell Is it available in , In the father Shell Is it available in

1: establish 2 Script

touch parent.sh
touch child.sh

2： modify parent Script files

vi parent.sh

#!/bin/bash
name="parentName"
export name
# Call the subscript file 
sh child.sh

3： modify child Script files

vi child.sh

#!/bin/bash
echo "parent  As defined in name: ${name}"

4： Execute parent script

sh parent.sh

5: result

2 Special variables $n

2.1 grammar

$n

2.2 meaning

 Used to receive the parameters passed in when the script file is executed 
$0  Used to get the name of the current script file 
$1~$9,  Means to obtain the first input parameter to the 9 Three input parameters 
 The first 10 Format of more than input parameters : ${
     Numbers },  Otherwise, you can't get 

2.3 Execute script file to pass in parameter syntax

sh  Script files  parm1 parm2 ...

2.4 demo

Create script file demo.sh file , And print the name of the script file in the script file , The first input parameter , The second input parameter

vim demo.sh

#!/bin/bash

# Print the current script file name 
echo " Current script file name : ${0}"
# Print input parameters 
echo " The first input parameter : ${1}"
echo " The second input parameter : ${2}"

perform ：

3 Special symbolic variables $#

3.1 grammar

$#

3.2 meaning

Get the number of all input parameters

3.3 demo

Print demo.sh Enter the number of parameters .

vim demo.sh


#!/bin/bash

# Print the current script file name 
echo " Current script file name : ${0}"

# The number of input parameters is 
echo " The number of input parameters is : ${#}"


# Print input parameters 
echo " The first input parameter : ${1}"
echo " The second input parameter : ${2}"

4 Special variables $* [email protected]

4.1 grammar

$*、[email protected]

4.2 meaning

1. Do not use double quotation marks ,  Function as 
  $* and [email protected] Get all input parameters , The format is : $1 $2 ... $n
2. Use double quotes 
  "$*" All the parameters obtained are spliced into a string ,  The format is : "$1 $2 ... $n"
  "[email protected]" Get a set of parameter list objects ,  The format is : "$1" "$2" ... "$n"
   You can see the difference by printing all the input parameters in a loop 

Cyclic grammar ：

for var in  List variables 
do		#  Loop start 
    command   #  The loop body 
done    #  The loop ends 

4.3 demo

stay demo.sh Print out all input parameters in a cycle , Experience $* And [email protected] The difference between

#!/bin/bash

# Print the current script file name 
echo " Current script file name : ${0}"
# The number of input parameters is 
echo " The number of input parameters is : ${#}"
# Output all input parameters 
echo ' Use $* Direct output :' ${
    *}
echo ' Use [email protected] Direct output :' ${
    @}
# Cyclic output 
echo ' Loop through the output $* All the parameters :'
for temp in "$*"
do
echo ${
    temp}
done

echo ' Loop through the output [email protected] All the parameters :'
for temp in "[email protected]"
do
echo ${
    temp}    
done

5 Special symbolic variables $?

5.1 command

$?

5.2 meaning

Used to get previous Shell Exit status code of the command , Or the return value of the function

5.3 demo