尝试了有3种方法：
1.使用“=~”符号，注意前后必须要有空格！
** 可以输出正确结果,被匹配的字符串必须要有引号括起来！**
[clouder@ana53 bin]$ a1='hello.world'
[clouder@ana53 bin]$ a2='helloworld'
[clouder@ana53 bin]$ b='.'
[clouder@ana53 bin]$ if [[ ${a1} =~ '.' ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a2} =~ '.' ]];then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if [[ ${a1} =~ "." ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a2} =~ "." ]];then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if [[ ${a1} =~ "${b}" ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a2} =~ "${b}" ]];then echo "yes";else echo "no";fi
no
** 不能输出正确结果 **
[clouder@ana53 bin]$ a1='hello.world'
[clouder@ana53 bin]$ a2='helloworld'
[clouder@ana53 bin]$ b='.'
[clouder@ana53 bin]$ if [[ ${a1} =~ . ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a2} =~ . ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a1} =~ ${b} ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a2} =~ ${b} ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a1} =~ '${b}' ]];then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if [[ ${a2} =~ '${b}' ]];then echo "yes";else echo "no";fi
no
2.使用”==“加通配符wildcard，注意等号前后必须有空格，注意，通配符跟正则表达式有所区别，*表示匹配 0 或多个字符
** 可以输出正确结果 **
[clouder@ana53 bin]$ a1='hello.world'
[clouder@ana53 bin]$ a2='helloworld'
[clouder@ana53 bin]$ if [[ ${a1} == *.* ]];then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if [[ ${a2} == *.* ]];then echo "yes";else echo "no";fi
no
** 不能输出正确结果 ，通配符不能用括号括起来！**
[clouder@ana53 bin]$ a1='hello.world'
[clouder@ana53 bin]$ a2='helloworld'
[clouder@ana53 bin]$ if [[ ${a2} == "*.*" ]];then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if [[ ${a1} == "*.*" ]];then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if [[ ${a1} == '*.*' ]];then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if [[ ${a2} == '*.*' ]];then echo "yes";else echo "no";fi
no
3.使用echo + grep -q 选项
** 使用这种方法时匹配是否有"."会不正常，所以我们换成匹配普通字符，有没有括号都可以 **
[clouder@ana53 bin]$ a1='hello.world'
[clouder@ana53 bin]$ a2='helloworld'
[clouder@ana53 bin]$ a3="helloworlda"
[clouder@ana53 bin]$ if ( echo ${a1} |grep -q a );then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if ( echo ${a2} |grep -q a );then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if ( echo ${a3} |grep -q a );then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if ( echo ${a1} |grep -q 'a' );then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if ( echo ${a2} |grep -q 'a' );then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if ( echo ${a3} |grep -q 'a' );then echo "yes";else echo "no";fi
yes
[clouder@ana53 bin]$ if ( echo ${a1} |grep -q "a" );then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if ( echo ${a2} |grep -q "a" );then echo "yes";else echo "no";fi
no
[clouder@ana53 bin]$ if ( echo ${a3} |grep -q "a" );then echo "yes";else echo "no";fi
yes