1. Shell basic case
1. The first case: helloworld
#!/bin/bash
function example {
echo "Hello world!"
}
example
2. Print the running python process
#!/bin/sh
pidlist=`ps -aux | grep python | awk '{print $2}'`
echo $pidlist
3. Obtain and print parameters
#!/bin/bash
echo "$0 $1 $2 $3" // 传入三个参数
echo $# //获取传入参数的数量
echo $@ //打印获取传入参数
echo $* //打印获取传入参数
4. Write a for loop with a script
#!/bin/bash
s=0;
for((i=1;i<100;i++))
do
s=$[$s+$i]
done
echo $s
r=0;
a=0;
b=0;
for((x=1;x<9;x++))
do
a=$[$a+$x]
echo $x
done
for((y=1;y<9;y++))
do
b=$[$b+$y]
echo $y
done
echo $r=$[$a+$b]
5. Use the C language style for command
#!/bin/bash
#testing the C-style for loop
for (( i=1; i<=10; i++ ))
do
echo "The next number is $i"
done
6. While loop case
#!/bin/bash
s=0
i=1
while [ $i -le 100 ]
do
s=$[$s + $i]
i=$[$i + 1]
done
echo $s
echo $i
7. Use break to jump out of the outer loop
#!/bin/bash
# break n，默认为1
for (( a=1; a<=3; a++ ))
do
echo "Outer loop : $a"
for (( b=1; b < 100; b++ ))
do
if [ $b -gt 4 ]
then
break 2
fi
echo " Inner loop:$b"
done
done
8. Use the continue command
#!/bin/bash
#using the continue command
for (( var1 = 1; var1 < 15; var1++ ))
do
if [ $var1 -gt 5 ] && [ $var1 -lt 10 ]
then
continue
fi
echo "Iteration number:$var1"
done
9. case case
#!/bin/bash
case $1 in
1)
echo "wenmin "
;;
2)
echo "wenxing "
;;
3)
echo "wemchang "
;;
4)
echo "yijun"
;;
5)
echo "sinian"
;;
6)
echo "sikeng"
;;
7)
echo "yanna"
;;
*)
echo "danlian"
;;
esac
10. Determine whether two numbers are equal
num1=100
num2=100
if test $[num1] -eq $[num2]
then
echo '两个数相等！'
else
echo '两个数不相等！'
fi
11. Use double parentheses
#!/bin/bash
# using double parenthesis
var1=10
if (( $var1 ** 2 > 90))
then
(( var2 = $var1 ** 2))
echo "The square of $var1 if $var2"
fi
12. Use square brackets
#!/bin/bash
# using pattern matching
if [[ $USER == r* ]]
then
echo "Hello $USER"
else
echo "Sorry, I do not know you"
fi
13. Use of backticks
#!/bin/bash
#using the backtick character 会把反引号里面当作一条命令来执行
testing=`date`
echo "The date and time are:$testing"
14. String comparison
#!/bin/bash
#testing string equality
testuser=tiandi
if [ $USER = $testuser ]
then
echo "Welcome $testuser"
fi
15. Read the value in the list
#!/bin/bash
# basic for command
for test in Alabama Alaska Arizona
do
echo The next state is $test
done
16. Print 99 multiplication table
#!/bin/bash
for i in `seq 9`
do
for j in `seq $i`
do
echo -n "$j*$i=$[i*j] "
done
echo
done
17. Script writing sum function operation function xx()
#!/bin/bash
function sum()
{
s=0;
s=$[$1+$2]
echo $s
}
read -p "input your parameter " p1
read -p "input your parameter " p2
sum $p1 $p2
function multi()
{
r=0;
r=$[$1/$2]
echo $r
}
read -p "input your parameter " x1
read -p "input your parameter " x2
multi $x1 $x2
v1=1
v2=2
let v3=$v1+$v2
echo $v3
18. The user guesses the number
#!/bin/bash
# 脚本生成一个 100 以内的随机数,提示用户猜数字,根据用户的输入,提示用户猜对了,
# 猜小了或猜大了,直至用户猜对脚本结束。
# RANDOM 为系统自带的系统变量,值为 0‐32767的随机数
# 使用取余算法将随机数变为 1‐100 的随机数
num=$[RANDOM%100+1]
echo "$num"
# 使用 read 提示用户猜数字
# 使用 if 判断用户猜数字的大小关系:‐eq(等于),‐ne(不等于),‐gt(大于),‐ge(大于等于),
# ‐lt(小于),‐le(小于等于)
while :
do
read -p "计算机生成了一个 1‐100 的随机数,你猜: " cai
if [ $cai -eq $num ]
then
echo "恭喜,猜对了"
exit
elif [ $cai -gt $num ]
then
echo "Oops,猜大了"
else
echo "Oops,猜小了"
fi
done
19. Write a rock-paper-scissors game
#!/bin/bash
game=(石头 剪刀 布)
num=$[RANDOM%3]
computer=${game[$sum]}
echo "请根据下列提示选择您的出拳手势"
echo " 1. 石头"
echo " 2. 剪刀"
echo " 3. 布 "
read -p "请选择 1-3 ：" person
case $person in
1)
if [ $num -eq 0 ]
then
echo "平局"
elif [ $num -eq 1 ]
then
echo "你赢"
else
echo "计算机赢"
fi;;
2)
if [ $num -eq 0 ]
then
echo "计算机赢"
elif [ $num -eq 1 ]
then
echo "平局"
else
echo "你赢"
fi;;
3)
if [ $num -eq 0 ]
then
echo "你赢"
elif [ $num -eq 1 ]
then
echo "计算机赢"
else
echo "平局"
fi;;
*)
echo "必须输入1-3 的数字"
esac
20. Detect whether the current user is an administrator
#!/bin/bash
# 检测本机当前用户是否为超级管理员
if [ $USER == "root" ]
then
echo "您是管理员，有权限安装软件"
else
echo "您不是管理员，没有权限安装软件"
fi
21. Receive parameters
Pass in parameter 3 to run: sh demo.sh 3, the console will print: wo ai wenxing
#!/bin/bash -xv
if [ $1 -eq 2 ] ;then
echo "wo ai wenmin"
elif [ $1 -eq 3 ] ;then
echo "wo ai wenxing "
elif [ $1 -eq 4 ] ;then
echo "wo de xin "
elif [ $1 -eq 5 ] ;then
echo "wo de ai "
fi
22. Read the parameters passed in from the console
#!/bin/bash
read -t 7 -p "input your name " NAME
echo $NAME
read -t 11 -p "input you age " AGE
echo $AGE
read -t 15 -p "input your friend " FRIEND
echo $FRIEND
read -t 16 -p "input your love " LOVE
echo $LOVE
23. Get user input
#!/bin/bash
# testing the reading command
echo -n "Enter your name:"
read name
echo "Hello $name, welcome to my program"
read -p "Please enter your age: " age
days=$[ $age * 365 ]
echo "That makes you over $days days old"
#指定多个变量，输入的每个数据值都会分配给表中的下一个变量，如果用完了，就全分配各最后一个变量
read -p "Please enter name:" first last
echo "Checking data for $last. $first..."
#如果不指定变量，read命令就会把它收到的任何数据都放到特殊环境变量REPLY中
read -p "Enter a number:"
factorial=1
for (( count=1; count<=$REPLY; count++))
do
factorial=$[ $factorial * $count ]
done
echo "The factorial of $REPLY is $factorial"
24. According to the current time of the computer, return the greeting
#!/bin/bash
# 根据计算机当前时间,返回问候语,可以将该脚本设置为开机启动
# 00‐12 点为早晨,12‐18 点为下午,18‐24 点为晚上
# 使用 date 命令获取时间后,if 判断时间的区间,确定问候语内容
tm=$(date +%H)
if [ $tm -le 12 ];then
msg="Good Morning $USER"
elif [ $tm -gt 12 -a $tm -le 18 ];then
msg="Good Afternoon $USER"
else
msg="Good Night $USER"
fi
echo "当前时间是:$(date +"%Y‐%m‐%d %H:%M:%S")"
echo -e "\033[34m$msg\033[0m"
2. File operation
1. Write the string to the file
For example, write I love cls into the demo.txt file
#!/bin/bash
cd /home/wenmin/
touch demo.txt
echo "I love cls" >>demo.txt
2. Directory file count
#!/bin/bash
# count number of files in your PATH
mypath=`echo $PATH | sed 's/:/ /g'`
count=0
for directory in $mypath
do
check=`ls $directory`
echo $check
for item in $check
do
count=$(( $count + 1 ))
done
echo "$directory - $count"
count=0
done
3. Read data from the file
#!/bin/bash
# reading data from a file
count=1
cat test | while read line
do
echo "Line $count: $line"
count=$[ $count + 1 ]
done
echo "Finished processing the file"
4. Replication with script
#!/bin/bash
cp $1 $2
5. Use scripts to judge whether a file exists
#!/bin/bash
if [ -f file.txt ];then
echo "文件存在"
else
echo "文件不存在"
fi
6. Check whether there is a specified file in the specified directory
#!/bin/bash
if [ -f /home/wenmin/datas ]
then
echo "File exists"
fi
7. The script uses the tar command to back up all log files under /var/log every 5 weeks
#!/bin/bash
# 每周 5 使用 tar 命令备份/var/log 下的所有日志文件
# vim /root/logbak.sh
# 编写备份脚本,备份后的文件名包含日期标签,防止后面的备份将前面的备份数据覆盖
# 注意 date 命令需要使用反引号括起来,反引号在键盘<tab>键上面
tar -czf log-`date +%Y%m%d`.tar.gz /var/log
# crontab -e #编写计划任务，执行备份脚本
00 03 * * 5 /home/wenmin/datas/logbak.sh
8. sed file operation
#!/bin/bash
#向文件写入
sed '1,2w test1' test1
echo -e "next\n"
#从文件读取
sed '3r ./test' ./test
echo -e "next\n"
#从文件读取，并插入字符流
sed '/lazy/r test' test
#向数据流末尾添加数据
sed '$r test' test
echo -e "next1\n"
sed '/lazy/ {
r test
d
}' test
3. Utilities
1. Execute the script regularly
#!/bin/bash
# testing the at command
at -f 4.sh 22:10
2. Check how many IPs are connecting to the machine
#!/bin/bash
# 查看有多少远程的 IP 在连接本机(不管是通过 ssh 还是 web 还是 ftp 都统计)
# 使用 netstat ‐atn 可以查看本机所有连接的状态,‐a 查看所有,
# -t仅显示 tcp 连接的信息,‐n 数字格式显示
# Local Address(第四列是本机的 IP 和端口信息)
# Foreign Address(第五列是远程主机的 IP 和端口信息)
# 使用 awk 命令仅显示第 5 列数据,再显示第 1 列 IP 地址的信息
# sort 可以按数字大小排序,最后使用 uniq 将多余重复的删除,并统计重复的次数
netstat -atn | awk '{print $5}' | awk '{print $1}' | sort -nr | uniq -c
3. Real-time monitoring of local memory and hard disk remaining space
When the remaining memory is less than 500M and the remaining space of the root partition is less than 1000M, an alarm email will be sent to the root administrator
#!/bin/bash
# 实时监控本机内存和硬盘剩余空间,剩余内存小于500M、根分区剩余空间小于1000M时,发送报警邮件给root管理员
# 提取根分区剩余空间
disk_size=$(df / | awk '/\//{print $4}')
# 提取内存剩余空空间
mem_size=$(free | awk '/Mem/{print $4}')
while :
do
# 注意内存和磁盘提取的空间大小都是以 Kb 为单位
if [ $disk_size -le 512000 -a $mem_size -le 1024000 ]
then
mail ‐s "Warning" root <<EOF
Insufficient resources,资源不足
EOF
fi
done
4. Count the number of accounts that can log in to the computer in the current Linux system
#!/bin/bash
# 统计当前 Linux 系统中可以登录计算机的账户有多少个
#方法 1:
grep "bash$" /etc/passwd | wc -l
#方法 2：
awk -f : '/bash$/{x++}end{print x}' /etc/passwd
5. Kill the tomcat process and restart it
#!/bin/bash
#kill tomcat pid
pidlist=`ps -ef|grep apache-tomcat-7.0.75|grep -v "grep"|awk '{print $2}'` #找到tomcat的PID号
echo "tomcat Id list :$pidlist" //显示pid
kill -9 $pidlist #杀掉改进程
echo "KILL $pidlist:" //提示进程以及被杀掉
echo "service stop success"
echo "start tomcat"
cd /opt/apache-tomcat-7.0.75
pwd
rm -rf work/*
cd bin
./startup.sh #;tail -f ../logs/catalina.out
6. Use the return command to return the function
#!/bin/bash
# using the return command in a function
function db1 {
read -p "Enter a value:" value
echo "doubling the value"
return $[ $value * 2 ]
}
db1
echo "The new value is $?"
7. Install memcached server with script
#!/bin/bash
# 一键部署 memcached
# 脚本用源码来安装 memcached 服务器
# 注意:如果软件的下载链接过期了,请更新 memcached 的下载链接
wget http://www.memcached.org/files/memcached-1.5.1.tar.gz
yum -y install gcc
tar -xf memcached‐1.5.1.tar.gz
cd memcached‐1.5.1
./configure
make
make install
8. Back up the MySQL database
#!/bin/sh
source /etc/profile
dbName=mysql
tableName=db
echo [`date +'%Y-%m-%d %H:%M:%S'`]' start loading data...'
mysql -uroot -proot -P3306 ${dbName} -e "LOAD DATA LOCAL INFILE '# /home/wenmin/wenxing.txt' INTO TABLE ${tableName} FIELDS TERMINATED BY ';'"
echo [`date +'%Y-%m-%d %H:%M:%S'`]' end loading data...'
exit
EOF
9. One-click deployment of LNMP (RPM package version)
#!/bin/bash
# 一键部署 LNMP(RPM 包版本)
# 使用 yum 安装部署 LNMP,需要提前配置好 yum 源,否则该脚本会失败
# 本脚本使用于 centos7.2 或 RHEL7.2
yum -y install httpd
yum -y install mariadb mariadb-devel mariadb-server
yum -y install php php-mysql
systemctl start httpd mariadb
systemctl enable httpd mariadb
4. Graphical operation
1. Print the chessboard with color
#!/bin/bash
# 打印国际象棋棋盘
# 设置两个变量,i 和 j,一个代表行,一个代表列,国际象棋为 8*8 棋盘
# i=1 是代表准备打印第一行棋盘,第 1 行棋盘有灰色和蓝色间隔输出,总共为 8 列
# i=1,j=1 代表第 1 行的第 1 列;i=2,j=3 代表第 2 行的第 3 列
# 棋盘的规律是 i+j 如果是偶数,就打印蓝色色块,如果是奇数就打印灰色色块
# 使用 echo ‐ne 打印色块,并且打印完成色块后不自动换行,在同一行继续输出其他色块
for i in {
1..8}
do
for j in {
1..8}
do
sum=$[i+j]
if [ $[sum%2] -eq 0 ];then
echo -ne "\033[46m \033[0m"
else
echo -ne "\033[47m \033[0m"
fi
done
echo
done
2. Use the msgbox component
#!/bin/bash
dialog --title text --msgbox "This is a test" 10 20
3. Use the menu display command to operate
#!/bin/bash
function menu {
clear
echo
echo -e "\t\tSys Admin Menu\n"
echo -e "\t1. Display disk space"
echo -e "\t2. Display logged on users"
echo -e "\t3. Display memory usage"
echo -e "\t0. Exit program\n\n"
echo -en "\t\tEnter option:"
read -n 1 option
}
function diskspace {
clear
df -k
}
function whoseon {
clear
who
}
function menusage {
clear
cat /proc/meminfo
}
while [ 1 ]
do
menu
case $option in
0)
break;;
1)
diskspace;;
2)
whoseon;;
3)
menusage;;
*)
clear
echo "Sorry, wrong selection";;
esac
echo -en "\n\n\t\tHit any key to continue"
read -n 1 line
done
clear
4. Use the dialog command in the script
#!/bin/bash
# using dialog to create a menu
temp=`mktemp -t test.XXXXXX`
temp2=`mktemp -t test2.XXXXXX`
function diskspace {
df -k > $temp
dialog --textbox $temp 20 60
}
function whoseon {
who > $temp
dialog --textbox $temp 20 50
}
function menusage {
cat /proc/meminfo > $temp
dialog --textbox $temp 20 50
}
while [ 1 ]
do
dialog --menu "Sys Admin Menu" 20 30 10 1 "Display disk space" 2 "Display users" 3 "Display memory usage" 0 "Exit" 2> $temp2
if [ $? -eq 1 ]
then
break
fi
selection=`cat $temp2`
case $selection in
1)
diskspace;;
2)
whoseon;;
3)
menusage;;
0)
break;;
*)
dialog --msgbox "Sorry,invalid selection" 10 30
esac
done
rm -f $temp 2> /dev/null
rm -f $temp2 2> /dev/null
5. Use the select command
#!/bin/bash
# using select in the menu
function diskspace {
clear
df -k
}
function whoseon {
clear
who
}
function menusage {
clear
cat /proc/meminfo
}
PS3="Enter option:"
select option in "Display disk space" "Display logged on users" "Display memory usage" "Exit program"
do
case $option in
"Exit program")
break;;
"Display disk space")
diskspace;;
"Display logged on users")
whoseon;;
"Display memory usage")
menusage;;
*)
clear
echo "Sorry, wrong selection";;
esac
done
clear
Five. sed operation
1. Basics of sed editor
#!/bin/bash
#sed编辑器基础
#替换标记
sed 's/lazy/ht/' ./test
echo -e "next\n"
#可用的替换标记
#1.数字 表明新闻本将替换第几处模式匹配的地方
sed 's/lazy/ht/2' ./test
#2.g 表明新文件将会替换所有已有文本出现的地方
sed 's/lazy/ht/g' ./test
#3.p 表明原来行的内容要打印出来,替换后的
sed 's/lazy/ht/p' ./test
#4.w file 将替换的结果写到文件中
sed 's/lazy/ht/w test1' ./test
echo -e "next\n"
#替换字符
sed 's/\/bin\/bash/\/bin\/csh/' /etc/passwd
#或者
sed 's!/bin/bash!/bin/csh!' /etc/passwd
echo -e "next\n"
#使用地址
#1.数字方式的行寻址
sed '2s/lazy/cat/' ./test
sed '2,3s/lazy/cat/' ./test
sed '2,$s/lazy/cat/' ./test
#2.使用文本模式过滤器
sed '/tiandi/s/bash/csh/' /etc/passwd
echo -e "next\n"
#组合命令
sed '2{
s/fox/elephant/
s/dog/cat/
}' test
sed '2,${
s/fox/elephant/
s/dog/cat/
}' test
echo -e "next\n"
#删除行
sed '3d' ./test
sed '2,$d' ./test
sed '/number 1/d' ./test
#删除两个文本模式来删除某个范围的行，第一个开启删除功能，第二个关闭删除功能
sed '/1/,/3/d' ./test
echo -e "next\n"
#插入和附加文本
sed '3i\
This is an appended line.' ./test
sed '$a\
This is a new line of text.' ./test
#修改行
sed '3c\
This a changed line of text.' ./test
sed '/number 1/c\
This a changed line of text.' ./test
#替换两行文本
#sed '2,3c\
#This a changed line of text.' ./test
#转换命令，处理单个字符
#sed 'y/123/789/' ./test
echo -e "next\n"
#回顾打印
# p 打印文本行
# -n 禁止其他行，只打印包含匹配文本模式的行
sed -n '/number 3/p' ./test
#查看修改之前的行和修改之后的行
#sed -n '/3/{
#p
#s/line/test/p
#}' ./test
echo -e "next\n"
# 打印行号
sed '=' ./test
#打印指定的行和行号
#sed -n '/lazy/{
#=
#p
#}' ./test
#列出行 打印数据流中的文本和不可打印的ASCII字符，任何不可打印的字符都用它们的八进制值前加一个反斜线或标准C风格的命名法，比如用\t来代表制表符
sed -n 'l' ./test
2. Output the data with the specified number of rows at the end
#!/bin/bash
#输出末尾10行数据
sed '{
:start
$q
N
11,$D
b start
}' /etc/passwd
3. Delete specified blank lines and delete html tags
#!/bin/bash
#多个空格只保留一个
#sed '/./,/^$/!d' test
#删除开头的空白行
#sed '/./,$!d' test
#删除结尾的空白行
sed '{
:start
/^\n*$/{$d; N; b start}
}' test
#删除html标签
#有问题
#s/<.*>//g
#sed 's/<[^>]*>//g' test1
#sed 's/<[^>]*>//g;/^$/d' test1
4. Mode replacement
#!/bin/bash
#and符号，代表替换命令中的匹配模式，不管预定义模式是什么文本，都可以用and符号替换，and符号会提取匹配替换命令中指定替换模式中的所有字符串
echo "The cat sleeps in his hat" | sed 's/.at/"&"/g'
#替换单独的单词
echo "The System Administrator manual" | sed 's/\(System\) Administrator/\1 user/'
#在长数字中插入逗号
echo "1234567" | sed '{:start; s/\(.*[0-9]\)\([0-9]\{3\}\)/\1,\2/; t start}'
6. Gawk operation
1. Using variables
#!/bin/bash
#使用内建变量
# NF 当前记录的字段个数
# NR 到目前为止读的记录数量
#下面的程序在每行开头输出行号，并在最后输出文件的总字段数
gawk '{ total+=NF; print NR, $0 }END{ print "Total: ", total}'
gawk 'BEGIN {testing="This is a test"; print testing; testing=45; print testing}'
#处理数字值
gawk 'BEGIN{x=4; x= x*2+3; printx}'
#处理数组
gawk 'BEGIN{capital["Ill"] = "SprintField"; print capital["Ill"]}'
#遍历数组变量
gawk 'BEGIN{
var["a"] = 1
var["g"] = 2
var["m"] = 3
for( test in var)
{
print "Index:",test,"- Value:",var[test]
}
}'
print "------"
#删除数组变量
gawk 'BEGIN{
var["a"] = 1
var["g"] = 2
for (test in var)
{
print "Index:",test," - Value:", var[test]
}
delete var["g"]
print "----"
for (test in var)
{
print "Index;",test," - Value:", var[test]
}
}'
2. Use mode, structured command
#!/bin/bash
#正则表达式
gawk 'BEGIN{FS=","}
/11/{print $1}
' test
#if-else语句
gawk '{
if($1 > 20)
{
x=$1*20
print x
}
else
{
x=$1/2
print x
}
}' test
#while 语句
gawk '{
total = 0
i=1
while(i<4)
{
total+=$i
i++
}
avg = total/3
print "Average:".avg
}' test
#do-while语句
gawk '{
total=0
i=1
do
{
total += $i
i++
}while(total < 150)
print total }' test
#for语句
gawk '{
total = 0
for (i=1; i<4; i++)
{
total+=$i
}
avg = total/3
print "Average:".avg
}' test
3. Custom functions
#!/bin/bash
#gawk 自定义函数
gawk '
function myprint()
{
printf "%-16s - %s\n", $1, $4
}
BEGIN{FS="\n"; RS=""}
{
myprint()
}' test
4. Call function library and script
#!/bin/bash
#使用函数库和gawk脚本
gawk -f gawk函数库 -f gawk脚本 test
5. Output
#!/bin/bash
#print用于产生简单输出
#多个表达式的字符串值之间用输出字段分隔符分开
gawk '{ print $1, $2 }'
#输出字段分割符与输出记录分隔符存储在内建变量OFS与ORS中，
#初始情况下，OFS与ORS被设置成一个空格符与一个换行符，但它们的值可以在任何时候改变
#下面这个程序打印每一行的第1第2个字段，字段之间用分号分开，在每一行的第2个字段之后输出两个换行符
gawk 'BEGIN { OFS = ":"; ORS = "\n\n" }
{ print $1, $2 }'
#下面这个程序拼接第1个与第2个字段，两个字段之间没有输出字段分隔符插入
gawk '{ print $1 $2 }'
#这两句话等价
gawk '{ print }'
gawk '{ print $0 }'
#输出空行
gawk '{ print "" }'
#printf用于产生格式化输出
#printf不会自动换行，需要手动添加\n
#格式说明符以%开始，以转换字符结束
# - 表达式在它的域内左对齐，没有则右对齐
# width 为了达到规定的宽度，必要时填充空格
# .prec 字符串最大宽度, 或十进制数的小数部分的位数
gawk '{ printf ("Name:%-10sAge:%-5dWeight:%7.2f\n", $1, $2, $3) }'
#输出到文件
#重定向运算符>与>>用于将输出重定向到文件，文件名必须用双引号括起来
#下面这个程序将所有输入行的第1个与第3个字段输出到两个文件中：如果第3个字段大于100，则输出到bigpop，否则输出到smallpop
gawk '{ print($1, $3) > ($3 > 100 ? "bigpop" : "smallpop") }'
#输出到管道
#print的输出将以管道的方式传递给command
# Canada 3852
# China 3705
# USA 3615
# Brazil 3286
gawk '{ pop[$1]+=$2 }
END{ for(c in pop) printf("%15-s%6d\n", c, pop[c]) | "sort -nk 2"; close("sort -nk 2") }'
#关闭文件与管道
#语句close(expression)关闭一个文件或管道，文件或管道由expression指定。
#expression的字符串值必须与最初用于创建文件或管道的字符串值相同。
#在同一个程序中，如果你写了一个文件，而待会儿想要读取它，那么就需要调用close。
#某一时刻，同时处于打开状态的文件或管道数量最大值由实现定义。
close("sort -nk 2")