Shell Programming and Scripting

Basically, the output would just remain the same with no lines being swapped...I looked around and that "-v" command for awk, is only in certain versions of awk, so I might not be able to use it in the version I'm using.

Could you post the output of the following commands (copy/paste from your terminal):

Code:

printf "%d\n" 1 2 3 |
awk 'NR == ln1, NR == ln2 {
  _[++c] = $0
  if (NR == ln2 && j = c)
    while (++i <= c)
      print _[NR ~ "^("ln1"|"ln2")$"?j--:i]
  next
}1' ln1=1 ln2=3

Or if your shell supports process substitution:

Code:

% awk 'NR == FNR {
  if (NR ~ "^("ln1"|"ln2")$")
    _[++c] = $0
  next
  }
FNR ~ "^("ln1"|"ln2")$" { $0 = _[c--] }
1' ln1=1 ln2=3 <(printf "%d\n" 1 2 3) <(printf "%d\n" 1 2 3)
3
2
1

I get:
3
2
1

I guess maybe i just copied the code of the two initial examples incorrectly? I'll play around with it some more and see if i can get it working.

OK,
thank you for posting the result.

Hi, I'm a newbie in unix script. Currently i'm using script for my daily job. Can anyone here explain in detail above script? I mean the syntax and command line by line. I do understand the script swap the 3rd line with line 10. If i want to swap line no 2 with line no 3, i just need to change variable line=2 and line1=3 right?

TQ.

It should work, to learn this stuff is to read about it and find it out yourself, so try it out.

The idea of the script, to replace the 3th line with the 9th, is:

1. print all lines untill line 3-1 (2nd line)
2. place the 4th line untill line 9-1 (8th line) before the 3th line in the variable s separated by a newline
3. print the 9th line
4. print the variable s
5. print other lines after the 9th line

Code:

#!/bin/sh
 
line=3
line1=10

awk -v var="$line" -v var1="$line1" 'NR==var {
  s=$0
  for(i=var+1;i<var1;i++){
    getline;s=$0"\n"s
  }
  getline;print;print s
  next
}1' file

Explanation of the code:

Code:

awk -v var="$line" -v var1="$line1"

Place the shellvariables in awk variables.

Code:

NR==var

If the linenumber is equal to 3 execute the commands between the curly brackets {}

Code:

s=$0

Place the current line in the variable s

Code:

  for(i=var+1;i<var1;i++){
    getline;s=$0"\n"s
  }

Loop through the lines 4 till 8 and place the lines before the 3th line separated by a newline.

Code:

  getline;print;print s
  next

Read the next line (9th line), print the line, print the variable s and read the next line

Code:

1

awk evaluates the 1 as true and the prints the entire line by default, an equivalent of {print}.


Regards

Wow. Thanks for your prompt reply. Appreciate it. But i just wondering why the output between line 4-8 is in desending order. I try to play around with the loop so that it is in asc order but didn't get the idea. Sorry if this question is annoying you.

Let' say the input file is:

Code:

1
2
3
4
5
6
7
8
9
10

Expected result:

Code:

1
2
9
4
5
6
7
8
3
10

My result:

Code:

1
2
9
8
7
6
5
4
3
10

Rgrds.