awk tutorial

Merge multiple consecutive lines

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Input file:

$ cat infile.txt 

aid=33

pw=3

nn=90

aid=32

pw=30

nn=70

aid=56

pw=3

nn=93

Required:

Combine or merge every three consecutive lines of the above file so that the output becomes: 

aid=33,pw=3,nn=90

aid=32,pw=30,nn=70

aid=56,pw=3,nn=93

Awk solution: If line number is divisible by 3 then put a new line(\n) else put a comma(,) i.e. 

$ awk '{printf("%s%s", $0, (NR%3 ? "," : "\n"))}' infile.txt 

aid=33,pw=3,nn=90

aid=32,pw=30,nn=70

aid=56,pw=3,nn=93

Another way using Awk: 

$ awk 'NR%3{printf $0",";next;}1' infile.txt 

aid=33,pw=3,nn=90

aid=32,pw=30,nn=70

aid=56,pw=3,nn=93

Using UNIX paste command: 

$ paste -d"," - - - < infile.txt 

aid=33,pw=3,nn=90

aid=32,pw=30,nn=70

aid=56,pw=3,nn=93

A bash command line solution: 

$ while read line1; do read line2; read line3; echo "$line1,$line2,$line3"; done < infile.txt 

aid=33,pw=3,nn=90

aid=32,pw=30,nn=70

aid=56,pw=3,nn=93