Shell Programming and Scripting

I have file1 and file2
I lookup field3 from file2 in field1 of file1 and if there is a match, output field 2,3,5 from file2.
I now want to add field2 of file1 in the output.

I suspect what I have to do is read the entire line of file1 into a 2 dim array? pls help.

here is my code:


cat file1

Code:

foo,cmd1
bar,cmd2

cat file2

Code:

Hello,World,foo
Alice,Bob,bar
Egg,Spam,ham

output with current awk:

Code:

awk -F, 'FNR==NR {arr[$1];next} $3 in arr {OFS=","; print $2,$4,$5}' file1 file2
World,fi,fom
Bob,bie,doll

desired output:

Code:

World,fi,fom,cmd1
Bob,bie,doll,cmd2

Try:

Code:

awk -F, 'FNR==NR {arr[$1]=$2; next} $3 in arr {print $2,$4,$5,arr[$3]}' OFS=, file1 file2

indeed that works, thanks.
do you mind explaining this {arr[$1]=$2
and OFS=, at the end (as i thought the comma within the print brackets did the job)

Ok, since you already used arr[$1] to create an empty array element with the index of field 1, I used that to give it the value of field 2 instead, which then later gets referenced in the second part, when file 2 gets read. You could leave OFS where it was, but that means it would get set to a comma every time a new line is read from file2. This way it is only set once, before the files are being read, it is just more efficient.

sorry still a little confused.

so the sequence is:
1. load file1, field1 into arr until FNR==NR
2. perform the match condition i.e $3 in arr

at this point my array still contains the value of field 1, are we saying this then gets replaced with the value of field2?

good tip

When FNR==NR (the first file is being read), load field 2 ($2) into array with index of field 1 ($1), until FNR!=NR then the second file starts (and the first section of the script is now skipped). While we are reading file 2 line by line, print the fields of file 2 and recall the previously stored array value using field 3 of the second file ($3) as the index..

Ok I'm with you now.
That means when I load field 1 into the array, I've actually created an empty array element with my values from field 1 as index.
I was under the impression they are actually loaded as elements into the array with an incremental count 0,1,2,3,...n as index.
So in effect by the time the first part of the script completes, we have the following contents in that array:

Index, Value
foo,cmd1
bar,cmd2

Have I understood this correctly?