How to use AWK to continuously output lines from a file

问题

I have a file with multiple lines, and I want to continuously output some lines of the file, such as first time, print from line 1 to line 5, next time, print line 2 to line 6, and so on. I find AWK as a very useful function and I tried to write a code on my own, but it just outputs nothing. Following is my code

#!/bin/bash
for n in `seq 1 3`
do
  N1=$n
  N2=$((n+4))
  awk -v n1="$N1" -v n2="$N2" 'NR == n1, NR == n2 {print $0}' my_file >> new_file
done

For example, I have an input file called my_file

1 99 tut
2 24 bcc
3 32 los
4 33 rts
5 642 pac
6 23 caas
7 231 cdos
8 1 caee
9 78 cdsa

Then I expect an output file as

1 99 tut
2 24 bcc
3 32 los
4 33 rts
5 642 pac
2 24 bcc
3 32 los
4 33 rts
5 642 pac
6 23 caas
3 32 los
4 33 rts
5 642 pac
6 23 caas
7 231 cdos

回答1:

Could you please try following, written and tested with shown samples in GNU awk. Where one needs to mention all lines which needs to be printed in lines_from variable, then there is a variable named till_lines which tells us how many lines we need to print from a specific line(eg--> from 1st line print next 4 lines too). On another note, I have tested OP's code and it worked fine for me, its generating the output file with new_file since calling awk in bash loop is NOT good practice hence adding this as an improvement too here.

awk -v lines_from="1,2,3" -v till_lines="4" '
BEGIN{
  num=split(lines_from,arr,",")
  for(i=1;i<=num;i++){ line[arr[i]] }
}
FNR==NR{
  value[FNR]=$0
  next
}
(FNR in line){
  print value[FNR] > "output_file"
  j=""
  while(++j<=till_lines){ print value[FNR+j] > "output_file" }
}
'  Input_file  Input_file

When I see contents of output_file I could see following:

cat output_file
1 99 tut
2 24 bcc
3 32 los
4 33 rts
5 642 pac
2 24 bcc
3 32 los
4 33 rts
5 642 pac
6 23 caas
3 32 los
4 33 rts
5 642 pac
6 23 caas
7 231 cdos

Explanation: Adding detailed explanation for above.

awk -v lines_from="1,2,3" -v till_lines="4" '    ##Starting awk program from here and creating 2 variables lines_from and till_lines here, where lines_from will have all line numbers which one wants to print from. till_lines is the value till lines one has to print.
BEGIN{                                           ##Starting BEGIN section of this program from here.
  num=split(lines_from,arr,",")                  ##Splitting lines_from into arr with delimiter of , here.
  for(i=1;i<=num;i++){                           ##Running a for loop from i=1 to till value of num here.
    line[arr[i]]                                 ##Creating array line with index of value of array arr with index of i here.
  }
}
FNR==NR{                                         ##Checking condition FNR==NR which will be TRUE when 1st time Input_file is being read.
  value[FNR]=$0                                  ##Creating value with index as FNR and its value is current line.
  next                                           ##next will skip all further statements from here.
}
(FNR in line){                                   ##Checking condition if current line number is coming in array then do following.
  print value[FNR] > "output_file"               ##Printing value with index of FNR into output_file
  j=""                                           ##Nullifying value of j here.
  while(++j<=till_lines){                        ##Running while loop from j=1 to till value of till_lines here.
    print value[FNR+j] > "output_file"           ##Printing value of array value with index of FNR+j and print output into output_file
  }
}
'  Input_file Input_file                         ##Mentioning Input_file names here.

回答2:

Another awk variant

awk '
BEGIN {N1=1; N2=5}
arr[NR]=$0 {}
END {
    while (arr[N2]) {
        for (i=N1; i<=N2; i++)
            print arr[i] 
        N1++
        N2++
    }
}
' file

来源：https://stackoverflow.com/questions/63895366/how-to-use-awk-to-continuously-output-lines-from-a-file

标签

Linux

bash

shell

awk