Shell(BASH) 编程
SHELL PROGRAMMING
目录：
写在前面：
1.Hello World示例
</> hello.sh
#!/bin/bash # This is an example of bash HelloWorld # You can start shell programming with an Hello World example
echo 'Hello World'
保存该内容到hello.sh,然后在终端运行它 ｀./hello.sh` , 就会看到 `Hello World` 消息。
2.计算1+1=2
</> expr.sh
#!/bin/bash # # This example will bring you to bash shell more deeply. # Function: add two input numbers and then print the result. if [ $# -ne 2 ] # error handling then echo "Usage - $0 x y" # display help message echo " Where x and y are two nos for which I will print sum" exit 1 fi echo "Sum of $1 and $2 is `expr $1 + $2`"
原理: expr(evaluate expressions)命令： 例如 `expr 1 + 2` 将会输出 ３
要了解更多关于expr命令的知识，输入 `man expr`
正文：
我们都知道，计算机识别的是二进制语言，计算机指令也是用二进制来表示的，但这对我们来说却相当困难。所以在一些操作系统中就有一个特殊程序叫做shell, shell接受你输入的指令，并且如果它是正确的话，就会将该指令传递到内核。
shell是一个用户程序或者说是一种由计算机与用户交互的环境。shell是一种解释型语言，可以执行来自标准输入设备（键盘）或者是文件的命令。 Linux shell跟windows command 类似，但是前者功能更为强大。
shell有许多种，本文中主要介绍的是bash (Bourne Again shell), 一种比较流行的shell语言，很多unix系统中都会默认集成它。
2.1 shell 变量
２.1.1 设置环境变量
如果变量已存在，直接赋值就行 (注意，不同于windows, unix-like系统中，变量和路径大小写敏感 case-sensitivity)
LANG=he_IL.UTF-8
如果不存在，加上 `export`语句即可 （先设置了shell变量，再 export为了环境变量)
EDITOR=nano export EDITOR
2.1.2 检测环境变量
printenv # 打印当前所有的环境变量 printenv TERM # 打印`TERM`环境变量 echo $TERM # 输出`TERM`环境变量的值
２.1.3 清除环境变量
export TERM= # 设置为空 export -n TERM # un-export unset TERM # 删除变量 TERM
2.1.4 配置文件
- 系统变量
主要的配置文件：
｀/etc/environment｀ 非脚本，主要包含一些环境变量赋值表达式
｀/etc/profile.d/*.sh｀ （注意 `/etc/profile` 作为基础的配置文件，所以一般不直接编辑它)
- 用户变量
` ~/.pam_environment ` (一般由ＧＵＩ等程序修改，不要手动编辑)
`~/.profile` (run after `~/.pam_environment` has been read,可以覆盖 `.pam_environment`文件里的配置) 一般登录后生效
其他 bash： Shell config files such as ~/.bashrc, ~/.bash_profile, and ~/.bash_login are often suggested for setting environment variables. While this may work on Bash shells for programs started from the shell, variables set in those files are not available by default to programs started from the graphical environment in a desktop session.
一般如无特殊需要，修改｀~/.bashrc｀就行了。
２.1.5 shell参数
- $符号，取出变量值
$$ Shell本身的PID（ProcessID） $! Shell最后运行的后台Process的PID $? 最后运行的命令的结束代码（返回值） $- 使用Set命令设定的Flag一览 $* 所有参数列表。如"$*"用「"」括起来的情况、以"$1 $2 … $n"的形式输出所有参数。 $@ 所有参数列表。如"$@"用「"」括起来的情况、以"$1" "$2" … "$n" 的形式输出所有参数。 $# 添加到Shell的参数个数 $0 Shell本身的文件名 $1～$n 参数值
2.2 输入输出 （I/O)
input： read
output: echo
2.3 shell 算术
a=$((1 + 2 * 3));
b=$(expr 3 + 2);
echo $a
echo $b
2.4 引号与注释
- 单行注释 a shebang or "bang" line
使用#符号注释一行
#!/bin/bash # This is a comment of the helloworld, (shebang) echo "Hello World!"
- 多行注释 Mulitple line comment
1). 使用Here Document (<<COMMENT1 到 COMMENT1结束部分被注释)
#!/bin/bash echo "Say Something" <<COMMENT1 This is a Hello World comment 2 blah COMMENT1 echo "Hello World"
2). 使用 : shell builtin command (or do-nothing command)
#!/bin/bash : ' your comments here ' echo "Hello World"
man page of : builtin command
: [arguments]
No effect; the command does nothing beyond expanding arguments
and performing any specified redirections. A zero exit code is
returned.
2.5 管道Pipes
2.5 Filters
2.7 其他
3.1 if条件语句
语法：
if condition then command1 if condition is true or if exit status of condition is 0 (zero) ... ... fi
例子：
The cat command return zero(0) i.e. exit status, on successful, this can be used, in if condition as follows, Write shell script as
$ cat > showfile |
if-than-else-fi语法：
if condition then condition is zero (true - 0) execute all commands up to else statement else if condition is not true then execute all commands up to fi fi
嵌套if语句：
if condition then if condition then ..... .. do this else .... .. do this fi else
if condition
then
.....
..
do this
else
....
..
do this
fi
fi
test 命令 或 [真值语句]
test命令和[expr]都可以用来判断一条语句是否为真，如果该语句为真则返回0，否则返回非0值为假。
用法：
test expression OR [ expression ]
例子,判断一个数是否为正数：
$ cat > ispostive #!/bin/sh # # Script to see whether argument is positive # if test $1 -gt 0 then echo "$1 number is positive" fi
更多资料：（英文,更接近与代码，所以不翻译了）
test or [ expr ] works with
1.Integer ( Number without decimal point)
2.File types
3.Character string
For Mathematics, use following operator in Shell Script
| Mathematical Operator in Shell Script | Meaning | Normal Arithmetical/ Mathematical Statements | But in Shell | |
| For test statement with if command | For [ expr ] statement with if command | |||
| -eq | is equal to | 5 == 6 | if test 5 -eq 6 | if [ 5 -eq 6 ] |
| -ne | is not equal to | 5 != 6 | if test 5 -ne 6 | if [ 5 -ne 6 ] |
| -lt | is less than | 5 < 6 | if test 5 -lt 6 | if [ 5 -lt 6 ] |
| -le | is less than or equal to | 5 <= 6 | if test 5 -le 6 | if [ 5 -le 6 ] |
| -gt | is greater than | 5 > 6 | if test 5 -gt 6 | if [ 5 -gt 6 ] |
| -ge | is greater than or equal to | 5 >= 6 | if test 5 -ge 6 | if [ 5 -ge 6 ] |
NOTE: == is equal, != is not equal.
For string Comparisons use
| Operator | Meaning |
| string1 = string2 | string1 is equal to string2 |
| string1 != string2 | string1 is NOT equal to string2 |
| string1 | string1 is NOT NULL or not defined |
| -n string1 | string1 is NOT NULL and does exist |
| -z string1 | string1 is NULL and does exist |
Shell also test for file and directory types
| Test | Meaning |
| -s file | Non empty file |
| -f file | Is File exist or normal file and not a directory |
| -d dir | Is Directory exist and not a file |
| -w file | Is writeable file |
| -r file | Is read-only file |
| -x file | Is file is executable |
Logical Operators
Logical operators are used to combine two or more condition at a time
| Operator | Meaning |
| ! expression | Logical NOT |
| expression1 -a expression2 | Logical AND |
| expression1 -o expression2 | Logical OR |
3.2 循环语句 Loop
for循环：
语法1：
for { variable name } in { list } do execute one for each item in the list until the list is not finished (And repeat all statement between do and done) done
示例：
$ cat > testfor for i in 1 2 3 4 5 do echo "Welcome $i times" done
语法2：
for (( expr1; expr2; expr3 )) do ..... ... repeat all statements between do and done until expr2 is TRUE Done
示例：
$ cat > for2 for (( i = 0 ; i <= 5; i++ )) do echo "Welcome $i times" done
语法3：
嵌套for循环：
$ vi nestedfor.sh for (( i = 1; i <= 5; i++ )) ### Outer for loop ### do for (( j = 1 ; j <= 5; j++ )) ### Inner for loop ### do echo -n "$i " done echo "" #### print the new line ### done
for i in (seq 1 5)
do
echo $i
done
while 循环
语法：
while [ condition ] do command1 command2 command3 .. .... done
数组
array=( 1 2 3 4 )
for i in array; do
echo $i
done
str_array=(
"Hi"
“Nice to meet you!"
"Good"
)
for ((i=0; i<${#str_array[*]}; i++))
do
echo ${str_array[$i]}
done
3.3 case 语句
语法：
case $variable-name in pattern1) command ... .. command;; pattern2) command ... .. command;; patternN) command ... .. command;; *) command ... .. command;; esac
;; 符号相当于c++中的break语句
延伸知识： ;分号
是多个语句之间的分隔符，
例如下面这句：
if[XXXXXXXXXXXXX];then
它完全等效于下面的两句：
1: if[XXXXXXXXXXXXX] 2: then
3.4 函数 Function
语法：
定义：
function-name ( ){ command1 command2 ..... ... commandN return }
或者
function function-name() {
command...
echo "parameter1 is $1, parameter2 is $2 ..."
}
使用：
function-name
例子：
#！/bin/bash # # This is an example of using function in shell programming # Defination of the function SayHello(){ echo ‘Hello’ return # must to return } # Using the SayHello Function SayHello
3.5 如何debug
可以使用 -v 或 -x 选项来debug shell 脚本
语法：
sh option { shell-script-name } # OR bash option { shell-script-name }
-v Print shell input lines as they are read. #打印出读入的各行
-x After expanding each simple-command, bash displays the expanded value of PS4 system variable, followed by the command and its expanded arguments
4.1 shell 脚本编写风格
Shell Style Guide By Google
5.1 计算一个数的阶乘
#!/bin/bash # # Calculate the factorial of an input integer # 使用说明 n=0 # 定义三个变量 on=0 fact=1 echo -n "Enter number to find factorial : " # 提示用户输入 read n on=$n # 给变量赋值 while [ $n -ge 1 ] # 循环满足条件，变量大于或等于1 do fact=`expr $fact \* $n` n=`expr $n - 1` done # 终止循环 echo "Factorial for $on is $fact" # 打印出结果
5.2
//TODO
参考：
https://help.ubuntu.com/community/EnvironmentVariables
https://help.ubuntu.com/community/Beginners/BashScripting
特殊字符 http://tldp.org/LDP/abs/html/special-chars.html
浙公网安备 33010602011771号