How to merge every two lines into one from the command line?

Question

I have a text file with the following format. The first line is the \"KEY\" and the second line is the \"VALUE\".

KEY 4048:1736 string
3
KEY 0:1772 string
1         


        

Answer 1

Here is my solution in bash:

while read line1; do read line2; echo "$line1, $line2"; done < data.txt

Answer 2

There are more ways to kill a dog than hanging. [1]

awk '{key=$0; getline; print key ", " $0;}'

Put whatever delimiter you like inside the quotes.

---

References:

1. Originally "Plenty of ways to skin the cat", reverted to an older, potentially originating expression that also has nothing to do with pets.

Answer 3

perl -0pE 's{^KEY.*?\K\s+(\d+)$}{ $1}msg;' data.txt > data_merged-lines.txt

-0 gobbles the whole file instead of reading it line-by-line;
pE wraps code with loop and prints the output, see details in http://perldoc.perl.org/perlrun.html;
^KEY match "KEY" in the beginning of line, followed by non-greedy match of anything (.*?) before sequence of

1. one or more spaces \s+ of any kind including line breaks;
2. one or more digit (\d+) which we capture and later re-insert as $1;

followed by the end of line $.

\K conveniently excludes everything on its left hand side from substitution so { $1} replaces only 1-2 sequence, see http://perldoc.perl.org/perlre.html.

Answer 4

Although it seems the previous solutions would work, if a single anomaly occurs in the document the output would go to pieces. Below is a bit safer.

sed -n '/KEY/{
N
s/\n/ /p
}' somefile.txt

Answer 5

nawk '$0 ~ /string$/ {printf "%s ",$0; getline; printf "%s\n", $0}' filename

This reads as

$0 ~ /string$/  ## matches any lines that end with the word string
printf          ## so print the first line without newline
getline         ## get the next line
printf "%s\n"   ## print the whole line and carriage return

Answer 6

Another approach using vim would be:

:g/KEY/join

This applies a join (to the line below it) to all lines that have the word KEY in it. Result:

KEY 4048:1736 string 3
KEY 0:1772 string 1
KEY 4192:1349 string 1
KEY 7329:2407 string 2
KEY 0:1774 string 1