225 lines
5.5 KiB
Markdown
225 lines
5.5 KiB
Markdown
### 使用方式分类
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- 0 真 1 假
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- test 条件表达式
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- [ 条件表达式 ]，括号两边都有空格
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- [[ 条件表达式 ]] 支持正则，括号两边都有空格
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### test 条件表达式
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```
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me@me-EQ59:~/shell_demo$ ls
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passwd scripts
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me@me-EQ59:~/shell_demo$ test -e passwd
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me@me-EQ59:~/shell_demo$ echo $?
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0
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me@me-EQ59:~/shell_demo$ test -e passwds
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me@me-EQ59:~/shell_demo$ echo $?
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1
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me@me-EQ59:~/shell_demo$
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```
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### [ 条件表达式 ]
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```
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me@me-EQ59:~/shell_demo$ ls
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passwd scripts
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me@me-EQ59:~/shell_demo$ [ -d scripts ]; echo $?
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0
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me@me-EQ59:~/shell_demo$ [ -d script_dir ]; echo $?
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1
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me@me-EQ59:~/shell_demo$
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me@me-EQ59:~/shell_demo$ ls -l
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总计 8
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-rwxrwxrwx 1 root root 3311 6月 22 14:30 passwd
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drwxrwxr-x 3 me me 4096 6月 22 16:20 scripts
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lrwxrwxrwx 1 me me 6 6月 23 14:24 test1 -> passwd
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me@me-EQ59:~/shell_demo$ [ -L test1 ]; echo $?
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0
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me@me-EQ59:~/shell_demo$ mv passwd passwd.bak
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me@me-EQ59:~/shell_demo$ ls -l
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总计 8
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-rwxrwxrwx 1 root root 3311 6月 22 14:30 passwd.bak
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drwxrwxr-x 3 me me 4096 6月 22 16:20 scripts
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lrwxrwxrwx 1 me me 6 6月 23 14:24 test1 -> passwd
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me@me-EQ59:~/shell_demo$ [ -L test1 ]; echo $?
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0
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me@me-EQ59:~/shell_demo$
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```
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### [[ 条件表达式 ]]
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```
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me@me-EQ59:~/shell_demo$ ls
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passwd.bak scripts test1
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me@me-EQ59:~/shell_demo$ [[ -f passwd.bak ]]; echo $?
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0
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me@me-EQ59:~/shell_demo$ [[ -f test ]]; echo $?
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1
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me@me-EQ59:~/shell_demo$
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```
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### 取反判断
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- 表达式前添加 `! `
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```
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# 判断不存在 test 文件时为真
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me@me-EQ59:~/shell_demo$ [[ ! -f test ]]; echo $?
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0
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me@me-EQ59:~/shell_demo$
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```
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### 文件判断参数
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### 判断文件权限
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```
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me@me-EQ59:~/shell_demo$ test -r /etc/passwd; echo $?
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0
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me@me-EQ59:~/shell_demo$ test -w /etc/passwd; echo $?
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1
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me@me-EQ59:~/shell_demo$
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```
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### 判断文件新旧 && 相等
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- 文件新旧判断
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```
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me@me-EQ59:~/shell_demo$ ls -l
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总计 12
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-rwxrwxr-x 1 me me 3311 6月 23 14:39 passwd
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-rwxrwxrwx 1 root root 3311 6月 22 14:30 passwd.bak
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drwxrwxr-x 3 me me 4096 6月 22 16:20 scripts
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lrwxrwxrwx 1 me me 6 6月 23 14:24 test1 -> passwd
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me@me-EQ59:~/shell_demo$ test passwd -nt passwd.bak; echo $?
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0
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me@me-EQ59:~/shell_demo$ test passwd -ot passwd.bak; echo $?
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1
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me@me-EQ59:~/shell_demo$
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```
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- 文件是否为同一个文件
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```
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me@me-EQ59:~/shell_demo$ touch file1
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me@me-EQ59:~/shell_demo$ touch file2
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me@me-EQ59:~/shell_demo$ test file1 -ef file2; echo $?
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1
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me@me-EQ59:~/shell_demo$ [ file1 -ef file2 ]; echo $?
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1
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me@me-EQ59:~/shell_demo$
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```
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### 判断数字
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### 判断字符串
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### 多重条件判断
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- -a 或 && 逻辑与
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- -o 或 || 逻辑或
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```
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me@me-EQ59:~/shell_demo$ [ 1 -eq 1 -a 2 -lt 3 ]; echo $?
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0
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me@me-EQ59:~/shell_demo$ [ 1 -eq 1 -a 2 -gt 3 ]; echo $?
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1
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me@me-EQ59:~/shell_demo$ [ 1 -eq 1 ] && [ 2 -lt 3 ]; echo $?
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0
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me@me-EQ59:~/shell_demo$ [ 1 -eq 1 ] || [ 2 -gt 3 ]; echo $?
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0
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me@me-EQ59:~/shell_demo$
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```
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- && 前边为真，后边才会执行
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```
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me@me-EQ59:~/shell_demo$ id -u
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1000
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me@me-EQ59:~/shell_demo$ [ $(id -u) -eq 0 ] && echo "admin"
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me@me-EQ59:~/shell_demo$ [ ! $(id -u) -eq 0 ] && echo "not admin"
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not admin
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me@me-EQ59:~/shell_demo$
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```
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- || 前边为假，后边才会执行
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```
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me@me-EQ59:~/shell_demo$ id -u
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1000
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me@me-EQ59:~/shell_demo$ [ $(id -u) -eq 0 ] || echo "not admin"
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not admin
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me@me-EQ59:~/shell_demo$
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```
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- 逻辑运算符没有优先级
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```
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me@me-EQ59:~/shell_demo$ [ $(id -u) -eq 0 ] && echo "admin" || echo "not admin"
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not admin
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me@me-EQ59:~/shell_demo$
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me@me-EQ59:~/shell_demo$ [ 1 -eq 2 ] && ehco AAA || echo BBB && echo CCC
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BBB
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CCC
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me@me-EQ59:~/shell_demo$
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```
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### 数值比较类 C 风格
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- = 表示赋值
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- == 表示判断相等
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```
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me@me-EQ59:~/shell_demo$ ((1==2)); echo $?
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1
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me@me-EQ59:~/shell_demo$ ((1<=2)); echo $?
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0
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me@me-EQ59:~/shell_demo$ ((1!=2)); echo $?
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0
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me@me-EQ59:~/shell_demo$ ((`id -u` == 0)); echo $?
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1
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me@me-EQ59:~/shell_demo$ ((`id -u`==0)); echo $?
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1
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me@me-EQ59:~/shell_demo$
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```
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### 字符串判断
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- = 和 == 都表示判断
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```
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me@me-EQ59:~/shell_demo$ str1="hello world";str2="world"
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me@me-EQ59:~/shell_demo$ [ str1 = str2 ];echo $?
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1
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me@me-EQ59:~/shell_demo$ [ $str1 = $str2 ];echo $?
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-bash: [: 参数太多
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2
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me@me-EQ59:~/shell_demo$ [ "$str1" = "$str2" ];echo $?
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1
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me@me-EQ59:~/shell_demo$ [ "$str1" == "$str2" ];echo $?
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1
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me@me-EQ59:~/shell_demo$ [ "$str1" != "$str2" ];echo $?
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0
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me@me-EQ59:~/shell_demo$
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```
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### [] 与 [[]]区别
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- 判断是空字符串时`[]` 报错 `[[]]`不报错
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```
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me@me-EQ59:~/shell_demo$ A=
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me@me-EQ59:~/shell_demo$ echo $A
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me@me-EQ59:~/shell_demo$ [ $A = "hello" ]
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-bash: [: =: 需要一元运算符
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me@me-EQ59:~/shell_demo$ [[ $A = "hello" ]]
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me@me-EQ59:~/shell_demo$ [[ $A = "hello" ]]; echo $?
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1
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me@me-EQ59:~/shell_demo$
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```
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- 逻辑运算符 && || 不拆开写的时候需要
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```
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me@me-EQ59:~/shell_demo$ [ 1 -eq 1 -a 1 -gt 2 ]; echo $?
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1
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me@me-EQ59:~/shell_demo$ [ 1 -eq 1 && 1 -gt 2 ]; echo $?
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-bash: [: 缺少 "]"
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2
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me@me-EQ59:~/shell_demo$ [[ 1 -eq 1 && 1 -gt 2 ]]; echo $?
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1
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me@me-EQ59:~/shell_demo$ [[ 1 -lt 1 || 1 -gt 2 ]]; echo $?
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1
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me@me-EQ59:~/shell_demo$ [ 1 -lt 1 || 1 -gt 2 ]; echo $?
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-bash: [: 缺少 "]"
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1：未找到命令
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127
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me@me-EQ59:~/shell_demo$
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``` |