To interpret variables through shell scripts

1. Variable assignment, substitution, etc.
   

#!/bin/bash
#1. Assigning values to a single variable
Variable1=33 #将变量variable1赋值为33
Echo ${variable1} # #第一种显示方法为 ${variable1}
echo $variable 1 # #第二种显示方法为 $variable 1

variable2= "Hello World" #将变量variable2赋值为 "Hello World", need double quotes to avoid character separation
Echo $variable 2
#****************************************************************************

#2. Variable Set Variable assignment value
Variable4= "We are saying $variable 2" #变量赋值中使用另一个变量 $variable 2
Echo $variable 4

#*****************************************************************************

#3. Clears the variable, but does not initialize the variable.
unset variable4 #清除variable4变量
Echo $variable # #空白行表示variable4变量未被初始化

#*****************************************************************************

#4. Symbols: + and Symbols:-Same points and differences
#相同点: You cannot reassign a variable that has already been assigned a value
Colour=black #对变量colour赋值
echo "The Background is ${colour:=blue}" usage of the ##:= symbol: represents an unassigned variable, assigns value to it
echo "The Background is ${colour:-blue}" uses the ##:-notation: represents an unassigned variable, assigns value to it, but value value is not stored in the corresponding address space of variable
#区别:
Unset colour #将变量colour的赋值清除
echo "The Background is ${colour:-blue}" # #用:-Symbol to colour assignment
Echo $colour # #colour没有真正赋值
echo "The Background is ${colour:=blue}" # #用: = symbol assigned to colour
Echo $colour # #colour赋值了

#*******************************************************************************

#5. Symbol + variable The assigned value, reset its value
Echo ${colour+red} # #对已经赋值的colour, re-assigned to red, temporary assignment
Echo $colour # #显示原来的赋值

#******************************************************************************

#6.?   Or:? Displays system error messages for unassigned variable
# #变量color是否赋值, if you have already assigned a value, the assignment is displayed, and no assignment shows-bash:b:parameter null or not set
echo ${colour?} # #变量colour已经赋值了, the assignment is shown below
unset Colour # #清除colour赋值赋值
echo ${colour?} # #colour没有赋值,-bash:b:parameter null or not set is displayed below

#/bin/bash
Colour=blue # #将变量colour赋值
echo Colour
Read Only colour # #将变量colour赋值为只读
Colour=black # #将变量colour重新赋值, found unable to assign value
ReadOnly # #查看系统中所有的只读变量

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parameter of the variable is used

#!/bin/bash
Echo "The script name is: $"       # $ to indicate the script itself
Echo "Parameter #1: $"             # Represents a 1th argument, followed by
Echo Parameter #2: $ "
echo "Parameter #3: $"
echo "Parameter #4: $4"
echo "Parameter #5: $"
echo "Parameter #6: $6"
Echo "Param Eter #7: $7 "
echo" Parameter #8: $8 "
echo" Parameter #9: $9 "
echo" Parameter #10: ${10} "    # ${10} Use curly braces

echo "-------------------------"
echo "The number of command line parameters is: $#" # $ #表示传递到脚本的参数数量
echo "All of the command line parameters is: [email protected]" # [email protected] or $* all parameters passed to the script
echo "The process ID is: $$" # $$ indicates the process number that the script is running
echo "Did this script has any errors $?" # $? Indicates the exit status of a command, 0 means no error, and 0 indicates an error

#position脚本说明 $0,$1,$2,..., ${10},$*,$#,$$,$?
#这里用cat tr cut head tail sed awk less more paste to represent 10 parameters of $ ${10}

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Relationship of parent and child processes

#father. SH: The script outputs its own process and invokes the child process

#!/bin/bash
#输出父进程号
echo "Father Process ID is $$"

#定义本地变量并输出
Localvar= "Define a local variable."
echo "Localvar= $localvar"

#定义环境变量并输出
envvar= "Define a environment variable."
Export Envvar
echo "Envvar= $ENVVAR"

#调用child. Sh script, which is the creation of child processes
$PWD/child.sh

#child. Sh execution complete, output correlation variable value
echo "Return to Father process: $$"
echo "Localvar= $localvar"
echo "Envvar= $ENVVAR"

#child. SH: The script outputs its own process number and parent process number, redefining local variables and environment variables
#!/bin/bash

#输出自身进程号及父进程号
echo "Chile Process ID is $$"
echo "My Father Process ID is $PPID"

#输出本地变量和环境变量的当前值
echo "Localvar= $localvar"
echo "Envvar= $ENVVAR"

#重新定义本地变量和环境变量
Localvar= "Redefine this ocal variable."
envvar= "Redefine This environment variable."
echo "Localvar= $localvar"
echo "Envvar= $ENVVAR"

This article is from the "All Night" blog, please make sure to keep this source http://endmoon.blog.51cto.com/8921900/1616629

To interpret variables through shell scripts