shell 里awk 的用法

打印全部列
```
awk '{print $0}'
```
打印指定列
```
awk '{print $2，$4}'
```
打印指定列并拼接字符串
```
awk '{print $1,"hhah",$2}'
awk '{print $1"hahah"$2}'
```

按指定分隔符取列
```
awk -F: '{ print $1 }' 
```
打印某一列及后面所有列的内容
```
awk '{out=""; for(i=2;i<=NF;i++){out=out" "$i}; print out}'
```

打印最后一列，最后一列的前一列，NF表示最后一列的列号
```
awk '{print $NF, $(NF-1)}'
```

打印指定一行，NR表示行号
```
awk  'NR==6 {print $0}'
```

打印第六行，以 ：分隔开的第一列
```
awk -F ":" 'NR==6 {print $1}'
```

打印第4行以后的行
```
git log --pretty=format:"%H-%h:%h" -n 15 |cat -n | awk 'NR>4 {print $0}'
     5	1f021028e22d92119fa5a0821273596e0c37be87-1f02102:1f02102
     6	f36b0ad5a376edf485979b357af4ac1df87cc443-f36b0ad:f36b0ad
     7	e3776955f8f3592051603d2299b93d3b55cbc52a-e377695:e377695
     8	94c50a1fd810d5c1e62535fac8f6db3c01c4c476-94c50a1:94c50a1

git log --pretty=format:"%H-%h:%h" -n 15 |cat -n | awk 'NR<4 {print $0}'
git log --pretty=format:"%H-%h:%h" -n 15 |cat -n | awk 'NR<=4 {print $0}'
```

**条件用法**
打印包含 Merge branch 的行 用/strings/
```
git log --pretty=format:"%s" -n 15 |cat -n |awk '/Merge branch/ {print $0}'
```
打印第一列为10 的 那一行的第一列和第二列
```
awk '$1==10  {print $1 $2}'
```
打印第二列为Merge 的 那一行的第一列和第二列
```
awk '$2=="Merge"  {print $1 $2}'
```

**函数用法**
```
# toupper() 转换大写
git log --pretty=format:"%H" -n 15 |awk '{print toupper($1)}'
098004D5D82D37D18B2909AEF53C8D3A22104030
46CBDB3641371BA4516F9E0ECCCB66B8304D8D6A

# tolower() 转换小写
git log --pretty=format:"%H" -n 15 |awk '{print toupper($1)}'|awk '{print tolower($1)}'
098004d5d82d37d18b2909aef53c8d3a22104030
46cbdb3641371ba4516f9e0ecccb66b8304d8d6a

```

END前面的语句会对每一行都执行
```
git log --pretty=format:"%H %h" -n 2 |awk '{print toupper($0)}'| awk '{string=$1"%%"$2} {print string}'
098004D5D82D37D18B2909AEF53C8D3A22104030%%098004D
46CBDB3641371BA4516F9E0ECCCB66B8304D8D6A%%46CBDB3

git log --pretty=format:"%H %h" -n 2 |awk '{print toupper($0)}'| awk '{string=$1"%%"$2} END {print string}'
46CBDB3641371BA4516F9E0ECCCB66B8304D8D6A%%46CBDB3

git log --pretty=format:"%H %h" -n 2 |awk '{print toupper($0)}'| awk '{string=$1"%%"$2}{print string} END {print string}'
098004D5D82D37D18B2909AEF53C8D3A22104030%%098004D
46CBDB3641371BA4516F9E0ECCCB66B8304D8D6A%%46CBDB3
46CBDB3641371BA4516F9E0ECCCB66B8304D8D6A%%46CBDB3

## 标准计数
# 打印过程
seq 5|awk '{ total+=$1} {print "After add " $1,"total number is :" total } END {print total }'
After add 1 total number is :1
After add 2 total number is :3
After add 3 total number is :6
After add 4 total number is :10
After add 5 total number is :15
15
# 只计总数
seq 5|awk '{ total+=$1} END {print total }'
 15
```

BEGIN END 示例中哪一段默认参数有效
下方的例子表示 BEGIN 后面接的第一个{}的语句里，\$1\$0 无值，NF NR 为0 ，BEGIN 第二个{}开始到END 之前的才是循环体，之间的\$X NF NR 会按实际生效读值，END 之后的{} 里读的是最后一行的值，所以想要循环计数，{total+=$1}必须放在循环体里
```
seq 5|awk 'BEGIN {print "BEGIN LINE " $0,$1 "NF"NF "NR"NR} {total+=$1} {print $0$1 "NF"NF "NR"NR} {print "After add " $1,"total number is :" total } END {print "END LINE "total ,$0,$1 ,"NF"NF "NR"NR}'
BEGIN LINE  NF0NR0
11NF1NR1
After add 1 total number is :1
22NF1NR2
After add 2 total number is :3
33NF1NR3
After add 3 total number is :6
44NF1NR4
After add 4 total number is :10
55NF1NR5
After add 5 total number is :15
END LINE 15 5 5 NF1NR5

```

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