1. print the last field of records; print the last nth field with $(NF - n)

{ print $NF }

1. pipe 不能连续使用，只能有一个管道，而且管道的输出会直接去到标准输出，没有办法用变量收集
2. array, 实际上是类似于lua里面的table, 可以有数字键，也可以有字符串键

1. awk in fact, inspires languages like perl and ruby
2. awk is Turing complete
3. awk is dedicated for string processing

1. A lot of implicit thing, like default action, default pattern; it is because when awk is invented, keystrokes, in another word, IO resources is valuable. Many people share a small slice of CPU.

1. expression {action}, expression can be regex pattern, also common seen expressions something like NR == 2
2. in fact, regex pattern is a shorthand for $0 ~ /regex/
3. functions call in awk: () can be omitted, inspiring ruby somehow, and parameter separator can be either <space> or ,
4. there is array type in awk
5. it can load module with @load
6. you can call other command line tools in awk, also piping with | and redirecting with >

1. printf, just a C-like printf sharing the same features
2. A lot of C math functions, like atan2, sqrt, rand
3. 

NOTE: gsub does not work as this picture claims, it acutally replace the 1st arg with the 2nd

# substitute all `root` for `good`
ps aux | awk ' { gsub("root" , "good", $0); print }'

# NOTE: 1 index
# this program print usernames without the 1st letter
ps aux | awk '{ a = substr($1, 2); print a}'

1. Amazing material from FreedomBen
2. GNU awk documentation