Awk basic and practice

定义：Awk是一种程序语言，用来处理数据和产生报告。数据可来自标准输入，文件，管道输出。

格式：#awk '/pattern/ {action}' filename

术语：pattern, 样式是由正则表达式，或条件表达式，或两者共同的组合所构成的语句。

action, 动作是在大括号内的一个或多个语句，且以“，”隔开。

原理：样式可以和动作结合，也可以各自单独工作。样式控制大括号间的动作。

Practice script

# cat awk.sh
#/bin/bash

echo '#print the contenct of employees'
cat  employees;
echo ''
echo '#print line include eric'
awk '/^eric/' employees 

echo '#print $1,$2,$3,$4 in eric line'
awk '/eric/ {print $1,$2,$3,$4}' employees

echo '#print $1 $2 $3 $4 in eric line'
awk '/eric/ {print $1 $2 $3 $4}' employees

echo "#print date , month, year"
date | awk '{print "month:" $2 "\nyear:" $6}'
echo ""

echo '#display error in /var/log/message'
cat /var/log/messages | awk '/error/{print $3,$5,$6}'

echo '#print two tab'
awk '/beijing/{print "\t\t How are you doing, "$1"!"}' employees

echo '#print space'
awk '{print $1 " ID is " $3 "\n"}' employees

echo '#print $0,and the number of record'
awk '{print NR, $0 }' employees

echo 'print $0,and the number of record'
awk '{print $0, NR }' employees

echo 'print $0,and the number of field'
awk '{print $0, NF }' employees

echo 'matching first line is frank, and show $1, $2'
awk '$1 ~/frank/ {print NR,$1,$2}' employees

echo 'matching first line is not frank, and show $1, $2'
awk '$1 !~/frank/ {print NR,$1,$2}' employees

echo 'matching line from frank to green, and show $1, $2'
awk '/frank/,/green/ {print $1,$2}' employees

echo '#print line3 bigger then 200000'
cat employees | awk '$3>200000'
echo ""

echo '#print number bigger then 200000'
cat employees | awk '$3>200000 {print "they are: " $1}' 

echo '#print line3 less then 200000'
cat employees | awk '$3<200000'
echo ""

echo '#print the result of $3*$4'
awk '$1 ~/frank/ {salary=$3 * $4; print salary}' employees

Output of the script

# ./awk.sh
#print the contenct of employees
eric    beijing
john    xian
mark    henan
frank    tokoyo
green    england          

#print line include eric
eric    beijing
#print $,$,$,$ in eric line
eric beijing
#print $ $ $ $ in eric line
ericbeijing12345610
#print date , month, year
month:Sep
year:

#display error in /var/log/message
#print two tab
         How are you doing, eric!
#print space
eric ID is 

john ID is 

mark ID is 

frank ID is 

green ID is 

#print $,and the number of record
 eric    beijing
 john    xian
 mark    henan
 frank    tokoyo
 green    england
print $,and the number of record
eric    beijing
john    xian
mark    henan
frank    tokoyo
green    england
print $,and the number of field
eric    beijing
john    xian
mark    henan
frank    tokoyo
green    england
matching first line is frank, and show $, $
 frank tokoyo
matching first line is not frank, and show $, $
 eric beijing
 john xian
 mark henan
 green england
matching line from frank to green, and show $, $
frank tokoyo
green england
#print line3 bigger then
john    xian
mark    henan
frank    tokoyo
green    england          

#print number bigger then
they are: john
they are: mark
they are: frank
they are: green
#print line3 less then
eric    beijing       

#print the result of $*$