老李分享：《Linux Shell脚本攻略》 要点（四）
1、IP地址的正则表达式： [0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}
2、grep用法
//在多级目录中对文本进行递归检索
[root@localhost program_test]# grep "yang" ./ -Rn
./test.txt:6:laoyang
./right.txt:1:1 yang man
//忽略大小写匹配
[root@localhost program_test]# echo hello world | grep -i "HELLO"
hello world
//递归搜索所有.c和.cpp文件
[root@localhost program_test]# grep "main()" . -r --include *.{c,cpp}
./hello.c:int main()
sin.c:int main()
hello.cpp:int main()
//匹配某个结果之后的几行
[root@localhost program_test]# echo -e "a
b
c
a
b
c"| grep a -A 1
a
b
--
a
b
3、cut命令
cut,将文本按照列进行切割的小工具。
//-d分界符; -f要提取的列
[root@localhost program_test]# cut -d ":" -f5 --complement passwd_yang
root:x:0:0:/root:/bin/bash
bin:x:1:1:/bin:/sbin/nologin
[root@localhost program_test]# cut -c1-5 passwd_yang
root:
bin:x
daemo
adm:x
//统计特定文件中的词频
[root@localhost program_test]# cat word_freq.sh
#!/bin/bash
if [ $# -ne 1 ];
then
echo "Usage: $0 filename"
exit -1
fi
filename=$1
egrep -o "[[:alpha:]]+" $filename |
awk '{ count[$0]++ }
END { printf("%-14s%s ","word","Count");
for(ind in count)
{ printf("%-14s%d ",ind,count[ind]); } }'
4、sed命令（stream editor 流编辑器)
适用文本处理.
//1.替换,从第3个开始替换
[root@localhost program_test]# echo this thisthisthis | sed 's/this/THIS/3g'
this thisTHISTHIS
//2.删掉空白行
[root@localhost program_test]# sed '/^$/d' choice.sh
//3.已匹配的字符串标记&
[root@localhost program_test]# echo this is an example | sed 's/w+/[&]/g'
[this] [is] [an] [example]
//4.替换举例.
[root@localhost program_test]# cat sed_data.txt
11 abc 111 this 9 file contains 111 11 88 numbers 0000
[root@localhost program_test]# cat sed_data.txt | sed 's/[0-9]{3}/NUMBER3/g'
11 abc NUMBER3 this 9 file contains NUMBER3 11 88 numbers 0000
//5.实战举例
获取ntp同步的错误信息(假定当前设备没有联网）
举例一：ntpdate 8.8.8.8
15 Jan 07:28:26 ntpdate[7137]: bind() fails: Permission denied
举例二：ntpdate google.com
[root@localhost cutDemo]# ntpdate msf22.com
Error resolving msf22.com: Name or service not known (-2)
15 Jan 07:30:54 ntpdate[7169]: Can't find host msf22.com: Name or service not known (-2)
15 Jan 07:30:54 ntpdate[7169]: no servers can be used, exiting
想获取[71**]:后的出错信息，之前的删除。脚本如下：
[root@localhost cutDemo]# ntpdate msft22.com 2>&1 | sed 's/.*]: //g'
Error resolving msft22.com: Name or service not known (-2)
Can't find host msft22.com: Name or service not known (-2)
no servers can be used, exiting
解释: ntpdate msft22.com 2>&1 //2>&1 标准输错重定向到标准输出。
sed 's/.*]: //g' //删除文件中"]:"前面的字符串。
5、awk工具,用于数据流，对列、行进行操作。
//1)、awk的实现方式
[root@localhost program_test]# echo -e "line1
line2" | awk 'BEGIN { print "begin...
" } { print } END { print "end...
" }'
begin...
line1
line2
end...
//2)、awk实现累加求和
[root@localhost program_test]# seq 5 | awk 'BEGIN { sum=0; print "summary:" } { print $1"+"; sum+=$1; } END { print "=="sum }'
summary:
1+
2+
3+
4+
5+
==15
//3)、awk 设定定界符.
//-F 定界符 $NF 一行中的最后一个字段
[root@localhost program_test]# awk -F: '{ print $1 " " $NF }' /etc/passwd
root /bin/bash
bin /sbin/nologin
daemon /sbin/nologin
//4)、打印文件中的每个字母
[root@localhost program_test]# cat read_each_word.sh
cat hello.c |
( while read line;
do
#echo $line;
for word in $line;
do
#echo $word;
for((i=0;i<${#word};i++))
do
echo ${word:i:1} ;
done
done
done )
//5)、打印第4-6行内容
[root@localhost program_test]# seq 100 | awk 'NR==4, NR==6'
4
5
6
//6)、awk实现类似tac逆序的功能.
[root@localhost program_test]# seq 9 | awk '{ lifo[NR]=$0; lno=NR } END { print "NR = " NR; for(;lno>-1;lno--) { print lifo[lno]; } }'
NR = 9
9
8
7
6
5
4
3
2
1