How to parse text with awk?

• ref
  • https://stackoverflow.com/questions/6284560/how-to-split-a-variable-by-a-special-character/6284596

Awk Syntax

awk '(PATTERN1){...print something..} (PATTERN2){..print something..}'
awk 'PATTERN1{...print something..} PATTERN2{..print something..}'

for each line, if PATTERNN is matched, command in {} will be executed.

syntax

`awk ‘NR==1{print}’ [FILE]` `awk ‘NR==1’ [FILE]` note for line 1, print whole line `awk ‘NR==1{}’ [FILE]` note for line 1, {} = don’t do anything `awk ‘NR==1{print} {print}’ [FILE]` note {} without condition is the same as condition always set to True. for eaech line, each condition will be read 1 time so this example line 1 will be printed 2 times while the rest of the line will be printed 1 time. `awk ‘($0 ~ e$){print $0}’ [FILE]` `awk ‘$0 ~ e$/{print $0}’ [FILE]` `awk ‘/e$/{print $0}’ [FILE]` :awk:regex:example:terminology note print line if first value ends with e. ~ indicate that if statement of the rigth is matched, condition will be true. /\<\> is regex

Usecase of how to use awk.

split input text by ‘x’

echo 1920x1080 | awk -F"x" '{print $1, $2}'

split input text from a line

echo '$2 = 1920x1080' | awk -F"x" 'sub(/\$[0-9] += +/, "", $1){print $1, $2}'

writing function in .awk extension file

example 1

Goal: rounding number using awk

1. create ‘test.awk’

      func round(n){
          n = n + 0.5
          n = int(n)
          return  n
          }
      /^w/ && $2 9000 (print $1, $2/1024, round($2/1024) "K")
   

2. run

         awk -f test.awk [FILE]`
   

example 2

Goal: print number that is less than the current line number (line number start from 1)

expected output:

1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6
1 2 3 4 5 6 7
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10

Solutions:

1. create loop.awk

      func printloop(n){
          for(i=1;i<=n;i++){
              printf("%d ", i)
              }
          printf("
      ")
      }
   
      {printloop($1)}
   

2. run

      seq 10 | awk -f loop.awk
   

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