Merging the rows in a file using awk

Question

Can somebody explain the meaning of the below script please?

awk -F "," 's != $1 || NR ==1{s=$1;if(p){print p};p=$0;next}
            {sub($1,"",$0);p=p""$0;}
            END{print p}' file

The file has the following data:

2,"URL","website","aaa.com"
2,"abc","text","some text"
2,"Password","password","12345678"
3,"URL","website","10.0.10.75"
3,"uname","text","some text"
3,"Password","password","password"
3,"ulang","text","some text"
4,"URL","website","192.168.2.110"
4,"Login","login","admin"
4,"Password","password","blah-blah"

and the output is:

2,"URL","website","aaa.com","abc","text","some text",Password","password","12345678"
3,"URL","website","10.0.10.75","uname","text","some text""Password","password","password","ulang","text","some text"

this is a bit broad. What about indicating what is the part you don't understand? Also, running the script in my machine gives 3 lines of output, you are missing the last one including the block of "4"s — fedorqui
– fedorqui, Commented Jun 9, 2015 at 12:59
Hi, i am new to scripting. but i need this script . s=$1;if(p){print p};p=$0;next. This line i didnot understand. — nikhila reddy
– nikhila reddy, Commented Jun 9, 2015 at 14:59

karakfa · Accepted Answer · 2015-06-09 15:33:32Z

1

awk has this structure

pattern {action}

for your script, let's analyze the elements, first pattern

 s != $1 || NR == 1   # if the variable s is not equal to first field
                      # or we're operating on first row

first action

 s = $1   # assign variable s to first field
 if (p) {  # if p is not empty, print
     print p
 }
 p = $0    # assign the current line to p variable
 next      # move to next, skip the rest

next pattern is missing, so the action will apply to all rows

 sub($1, "", $0)   # same as $1="", will clear the first field
 p = ((p "") $0)   # concat new line to p

last pattern is special reserved word END, only applied when all rows are consumed (there is counterpart BEGIN that's applied before the file is opened)

 END {
      print p      # print the value of p
 }

answered Jun 9, 2015 at 15:33

karakfa

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1 Comment

Ed Morton Over a year ago

if p is not empty should be if p is not the null string and does not evaluate numerically to zero. sub($1, "", $0) is not the same as $1="" as the former will replace the regexp contained in $1 in $0 (try both if $1 is .*) and it will not cause recompilation of $0 (try both with tabs between fields). p=p""$0 is an obfuscated form of p=p $0. I know a lot of awk documentation talks about pattern { action } but that's misleading at best - it's really condition { action }.

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