总结一篇shell调试技巧及常见的脚本错误

#使用
[root@game ~]# sh [-xvn] test.sh

#参数解释：
-x：将执行的脚本内容输出出来,可以看到执行的过程
-n：不执行脚本，检查脚本语法是否有问题，给出错误的提示
-v：执行脚本时，先将脚本的内容输出到屏幕上，再执行脚本，如果有错误给出错误提示

#说明：不会执行脚本，只检查有无语法错误，如果没有检测到，就无输出
[root@game scripts]# cat test7.sh 
#!/bin/bash
echo "guoke123"
[root@game scripts]# sh -n test7.sh 
#脚本没有语法错误，所以没有输出

#演示脚本存在语法错误
#!/bin/bash
if [ `netstat -untpl | grep httpd | wc -l` -gt 0 ];then
    echo "httpd is Running
else
    echo "httpd service down" | mail -s "httpd" 10588@qq.com
    systemctl restart httpd
fi
[root@game scripts]# sh -n test1.sh 
test1.sh: line 5: unexpected EOF while looking for matching `"'
test1.sh: line 8: syntax error: unexpected end of file
#提示：第5行结尾没有双引号

[root@game scripts]# sh -v test1.sh 
#!/bin/bash
if [ `netstat -untpl | grep httpd | wc -l` -gt 0 ];then
    echo "httpd is Running
else
    echo "httpd service down" | mail -s "httpd" 10588@qq.com
    systemctl restart httpd
fi
test1.sh: line 5: unexpected EOF while looking for matching `"'
test1.sh: line 8: syntax error: unexpected end of file

#!/bin/bash
if [ `netstat -untpl | grep httpd | wc -l` -gt 0 ];then
    echo "httpd is Running"
else
    echo "httpd service down" | mail -s "httpd" 10588@qq.com
    systemctl restart httpd
fi

#打印执行过程
[root@game scripts]# sh -x test1.sh 
++ netstat -untpl
++ wc -l
++ grep httpd
+ '[' 0 -gt 0 ']'
+ echo 'httpd service down'
+ mail -s httpd 10588@qq.com
+ systemctl restart httpd

使用set -x可以缩小调试的作用域范围
set -x开启调试功能，set +x关闭调试功能

#示例
#!/bin/bash
set -x
for i in `seq 9`
do
    for n in `seq 9`
    do
	[ $i -ge $n ] && echo -en "$i x $n" = $(expr $i \* $n)
    done
set +x
echo " "
done

#执行效果
[root@game scripts]# sh test6.sh 
++ seq 9
+ for i in '`seq 9`'
++ seq 9
+ for n in '`seq 9`'
+ '[' 1 -ge 1 ']'
++ expr 1 '*' 1
+ echo -en '1 x 1' = 1
1 x 1 = 1+ for n in '`seq 9`'
+ '[' 1 -ge 2 ']'
......
+ '[' 1 -ge 8 ']'
+ for n in '`seq 9`'
+ '[' 1 -ge 9 ']'
+ set +x
#提示：只调试了set -x 和set +x 这个作用域

一般在可能出现问题的脚本的重要部分加入echo命令

#示例
[root@game scripts]# cat test8.sh 
#!/bin/bash
read -p "please input tow num:" a b
echo $a $b
exit

#执行效果
[root@game scripts]# sh test8.sh 
please input tow num:1 2
1 2

[root@game scripts]# cat test.sh 
#!/bin/bash

yum install net-tools -y >/dev/null
if [$? -eq 0]
    then
	echo "install success"
    else
	echo "install fail"
fi

#执行：报错
[root@game scripts]# sh test.sh 
test.sh: line 4: [0: command not found
install fail
#提示：错误在第四行

#成对的符号例如：()、[]、""、''等
#示例[]中括号没有写全
[root@game scripts]# cat test1.sh 
#!/bin/bash

if [ `netstat -untpl | grep httpd | wc -l` -gt 0 ;then
    echo "httpd is Running"
else
    echo "httpd service down" | mail -s "httpd" 10588@qq.com
    systemctl restart httpd
fi

#执行效果
[root@game scripts]# sh test1.sh 
test1.sh: line 3: [: missing `]'

[root@game scripts]# cat test2.sh 
#!/bin/bash

if [ `netstat -untpl | grep mysqld | wc -l` -gt 0 ];then
    echo "mysqld is Running"
else
    echo "mysqld service down" | mail -s "mysqld" 1792988@qq.com
    systemctl restart mysqld

#执行效果
[root@game scripts]# sh test2.sh 
test2.sh: line 8: syntax error: unexpected end of file
#执行脚本会提示第8行语法错误

#示例1：for循环的done少了个e
[root@game scripts]# cat test3.sh 
#!/bin/bash
usage(){
    echo "directory not found"
}

[ ! -d /test ] && usage && exit 1
cd /test

for i in `ls`
do
    echo $i
don

#执行效果
[root@game scripts]# sh test3.sh 
test3.sh: line 13: syntax error: unexpected end of file

#示例2：if条件语句的then少了n
[root@game scripts]# cat test2.sh 
#!/bin/bash

if [ `netstat -untpl | grep mysqld | wc -l` -gt 0 ];the
    echo "mysqld is Running"
else
    echo "mysqld service down" | mail -s "mysqld" 1792988@qq.com
    systemctl restart mysqld
fi
#执行效果
[root@game scripts]# sh test2.sh 
test2.sh: line 5: syntax error near unexpected token `else'
test2.sh: line 5: `else'
#执行脚本之后会提示语法错误
#需要注意的是shell脚本解释器一般不会很精确的定位到错误，需要上下联都看一下