Shell Programming Basics

Shell Learning Notes

# #变量

# #普通变量:
EG1:
Name=axe
Echo $name
ps. equals two times cannot have a space, otherwise it will be an error.
EG2:
Name= "Axe Prpr"
Echo $name
Or
Name= ' Axe PRPR '
Echo $name
PS. Double quotes can refer to other variables, single quotation marks are not allowed.
eg
Name=axe
Fullname= "$name PRPR"
Echo $fullname
EG3:
Version= ' uname-a ' (referencing a command in a variable)
Echo $version
EG4:
Amplification of variables:
Echo $PATH
Path=${path}:/home/axe
Echo $PATH
Or
Path= "$PATH":/home/axe

# #环境变量:
ENV View:
' [Email protected]:~$ env
Lc_paper=zh_cn. UTF-8
Lc_address=zh_cn. UTF-8
Xdg_session_id=6
Lc_monetary=zh_cn. UTF-8
term=vt100
... '
or export view.
eg
Name=axe
Echo $name
Bash (Create a new subroutine)
echo $name (no output at this time)
Exit
Export name
Bash
Echo $name

# #取消变量
eg
Name=axe
Echo $name
unset name (cancel variable)
Echo $name

# #只读变量
eg
Name=axe
ReadOnly Name
NAME=PRPR (Error at this time)

# #特殊变量
Eg.eg:
VI test2.sh
' #!/bin/sh
Echo $$ #表示当前shell进程的ID
Echo #表示当前的文件名
echo $ #表示脚本或函数的输入值
Echo $# #表示传递给脚本或函数的参数个数
Echo $* #表示传递给脚本或函数的所有参数
echo [email protected] #表示传递给脚本或函数的所有参数
echo $? #表示函数的返回值
#区别下 $* and [email protected]
For I in $*
Do
Echo $i
Done
For i in [email protected]
Do
Echo $i
Done
For i in "$*"
Do
Echo $i
Done
For i in "[email protected]"
Do
Echo $i
Done
#不加 "", two output is "$" and "$". Add "", $* will be "$1,$2." Output
#可以看出没什么吊用
`
wq!
chmod +x test2.sh
./test2.sh a B
The result of the execution is:
' [email protected]:~/test$./test2.sh a B
12304
./test2.sh
A
2
A b
A b
0
A
B
A
B
A b
A
B
PS. Here's $? The execution result is 0, which indicates that the exit status of the previous command on the shell is success.

# #算术运算
Bash does not support simple operations and can be implemented with expr:
eg
VI test3.sh
' #!/bin/sh
Value1= ' Expr 2 + 2 '
value2= ' Expr 2-2 '
value3= ' Expr 2 \* 2 '
value4= ' Expr 2/2 '
echo $value 1
Echo $value 2
Echo $value 3
Echo $value 4
`
The output is: 4 0 4 1

# #关系运算
VI test4.sh
' #!/bin/sh
If [$1-eq $];then
echo "$1=$2"
Fi
If [$1-ne $];then
echo "$1!=$2"
Fi
If [$1-gt $];then
echo "$1>$2"
Fi
If [$1-lt $];then
echo "$1<$2"
Fi
If [$1-ge $];then
echo "$1>=$2"
Fi
If [$1-le $];then
echo "$1<=$2"
Fi
`
# #布尔运算符
eg
If [1-eq 2-o 1-lt 2];then echo true;fi;
If [1-ge 1-a 1-le 1];then echo true;fi;
if [! 1-eq 2];then Echo true;fi;

# #字符串运算符
eg
If [a = a];then echo true;fi;
if [A! = b];then echo true;fi;
If [-Z];then Echo true;fi;
If [-N a];then echo true;fi;
If [str];then echo True;fi;

# #文件测试运算符
File= "/home/axe/test/test1.sh"
If [-R $file];then Echo true;fi;
If [-W $file];then Echo ture;fi;
If [-X $file];then echo ture;fi;
If [-S $file];then echo ture;fi; (empty)
If [-e $file];then echo ture;fi; (presence)
Rest:
`
The-B file detects whether the files are block device files and, if so, returns True.
The-C file detects whether the files are character device files and, if so, returns True.
The-D file detects whether the files are directories and, if so, returns True.
-F file to detect whether files are normal files (neither directories nor device files)
The-G file detects if the SGID bit is set and returns True if it is.
The-K file detects whether the files have a sticky bit set (Sticky bit), and returns True if it is.
The-P file detects whether the files are named pipes and, if so, returns True.
-U file detects whether the file has a SUID bit set and returns True if it is.
`
# #字符串
Name= "Axe Prpr"
Echo $name
echo ${#name} #表示字符串长度
echo ' expr index ' $name position in ' a ' #表示字符a在 $name
Name2= "Axe prpr $name" #双引号拼接字符串
Echo ${name:1:4} extract string

# #数组
Array= (a b C)
Echo ${array[1]}
echo ${array[*]} #或者 @
echo ${#array [*]} #获取长度

# #条件选择
#if Else elif fi
eg
A=b
If [-N $a];then echo True;elfi [-Z $a];then echo ture;fi;

#case in;; Esac
eg
#!/bin/sh
Case $ in
Axe) echo "is a name"
;;
0904) echo "is a date"
;;
Esac

#for in Do
eg
For file in/home/axe/test/*.sh
Do
Echo $file
Done

#while do
eg
While read File;do echo "Get $file", echo "type ctrl+d to terminate";d one;

#until do
eg
A=100;until [' Expr $a-1 '-le 0];d o a= ' expr $a-1 '; echo $a;d one; (Output 100-1)

#break, continue
Slightly

# #函数
eg
Function name () {
Name=axe
Echo $name
}
Name

EG2: return value of function
function Add () {
Return ' expr 1 + 2 '
}
Add
echo $?

Delete function using UNSET.F

EG3: Transfer of parameters
function Calputer () {
Case $ in
+) echo ' expr + $ $ ';;
-) echo ' expr $-$ ';;
*) echo ' expr $ \* $ ';;
/) echo ' expr/$ $ ';;
Esac
}
Calputer 1 + 2

# #重定向
eg
echo ' pwd ' > pwd.sh
Ls-l < pwd.sh

# #文件包含
Slightly

Shell Programming Basics