shell中怎么判断变量是不是以字母开头的

lostoasis

想要判断一个变量，如果这个变量是以小写字母开头的，就输出这个变量，请问下面这个为什么什么也不输出~~~~~~~~~~~~~~~
#!/bin/bash
aa=backup
if [[ $aa == "^[a-z]*" ]]
then
echo $aa
fi

songyc_2015

使用    =~

lostoasis

不行啊，没有结果输出
[:c10user:/home/TT_DB/ttingtest/ttingtest1]$ cat li
#!/bin/bash
a=backup
if [[ $a =~ "^[a-z]*" ]]
then
echo $a
fi

[:c10user:/home/TT_DB/ttingtest/ttingtest1]$ li
[:c10user:/home/TT_DB/ttingtest/ttingtest1]$



回复 2# songyc_2015


   

wh7211

1. #!/bin/bash
   
2. a="backup"
   
3. if [[ "$a" =~ ^[a-z]* ]];then
   
4. echo "$a"
   
5. else
   
6. echo "no"
   
7. fi

复制代码

lostoasis

感觉不对啊，a的值改成123backup,然后输出123backup,没有遵循以a-z字母开通的原则：
[:c10user:/home/TT_DB/ttingtest/ttingtest1]$ cat li
#!/bin/bash
a="123backup"
if [[ "$a" =~ ^[a-z]* ]];then
echo "$a"
else
echo "no"
fi

[:c10user:/home/TT_DB/ttingtest/ttingtest1]$ li
123backup



回复 4# wh7211


   

tuyajie

不知道我说没说清楚

1. [jay.liu@aliCloud ~]$ aa=\^\[a\-z\]\*
   
2. [jay.liu@aliCloud ~]$ echo $aa
   
3. ^[a-z]*
   
4. [jay.liu@aliCloud ~]$ if [[ $aa == "^[a-z]*" ]]
   
5. > then
   
6. > echo $aa
   
7. > fi
   
8. ^[a-z]*
   
9. 
   
10. [jay.liu@aliCloud ~]$ echo $aa
    
11. test
    
12. [jay.liu@aliCloud ~]$ if [[ $aa =~ ^[a-z]* ]]; then echo Y; else echo N; fi
    
13. Y
    
14. [jay.liu@aliCloud ~]$ if [[ $aa =~ "^[a-z]*" ]]; then echo Y; else echo N; fi
    
15. N

复制代码

jason680

回复 5# lostoasis


$ a="backup"; if [[ "$a" =~ ^[a-z] ]];then echo $a; fi
backup

$ a="123backup"; if [[ "$a" =~ ^[a-z] ]];then echo $a; fi

$ a="backup"; if [[ "$a" =~ ^[a-z]+$ ]];then echo $a; fi
backup

$ a="backup123"; if [[ "$a" =~ ^[a-z]+$ ]];then echo $a; fi
   

聆雨淋夜

用+别用*，*能匹配到0个字符

回复 5# lostoasis

用+不能用*  *能匹配到0个字符，在你的例子中用*就毫无意义了


   

wh7211

回复 5# lostoasis
把*换成+，比如："$a" =~ ^[a-z]+