Ngtjyty

I have the file

Line 1

Line 2 MATCH

Line 3

Line 4

Line 1

Line 2 MATCH

Line 3

Line 4

And I want to swap the line with "MATCH" and "Line 1" for every case. I tried to search in other questions, but those move the line with the match to the last line and I don't understand so well the code to remake my version for a final output like:

Line 2 MATCH

Line 1

Line 3

Line 4

Line 2 MATCH

Line 1

Line 3

Line 4

If the idea is to swap the MATCH line with the immediately preceding one, then something like this would do:

$ awk '!/MATCH/ { if (NR > 1) print prev; prev=$0} 

        /MATCH/ {print $0;} 

        END {print prev}' < file

Line 2 MATCH

Line 1

Line 3

Line 4

Line 2 MATCH

Line 1

Line 3

Line 4

The script holds the previous line in prev, printing and updating it on the non-matching lines. On lines matching the pattern, it prints the current line, leaving the previous in the variable to be printed next.

Special cases for the first line (NR==1) when there's no previous line to print, and for the END when we print the held line.

Using ed:

$ printf 'g/MATCH/m-2n,pn' | ed -s file

Line 2 MATCH

Line 1

Line 3

Line 4

Line 2 MATCH

Line 1

Line 3

Line 4

The m command moves the current line to the subsequent target address. Here, we find all lines matching MATCH (it's the g in front of the regular expression that makes this a "global" operation), and for each line move it one line up. The effect is that the MATCH lines swap places with the immediately preceding lines. We use -2 since the m command moves the line to after the targeted line.

The final ,p in the editing script just displays the modified editing buffer.

Using sed with a N;P;D cycle:

sed -e '$!N;s/(Line 1)(n)(.*MATCH.*)/321/;t' -e 'P;D' infile

This will swap only if the line with MATCH is preceded by Line 1: the t without label branches to the end of script if successful and so it avoids another swap if any Line 1 is followed by consecutive lines with MATCH. Adjust the regex for any leading/trailing blanks.

Using sed editor, we can swap two lines one of which contains Match keyword with the one preceding it.

 $ sed -e '

       /MATCH/!{

         x;1!p;$!d;g;q

       }

       $G

   '  input.txt



 Line 2 MATCH

 Line 1

 Line 3

 Line 4

 Line 2 MATCH

 Line 1

 Line 3

 Line 4

sed "s/line 2 match//g"|sed "s/line 1/line 2 matchn&/g"

Above command worked fine