print the 2nd line above the pattern 2

[frankli]

Just wandering if there is a easy way in awk to print the 2nd line above the pattern line

abc
def
hij
klm

locate klm to print out def.

Thanks in advance to my favorite AWK list!

 

[PHV]

A starting point:

awk '{a[NR%3]=$0}/klm/{print a[(NR-2)%3]}' /path/to/input

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886

 

[frankli]

Hi PH,

It works. Thanks.

I also tried below it works too, please give a tip on how to understand NR%3

awk '{a[NR]=$0}/klm/{print a[NR-2]}' /path/to/input


Regards,
-frank

PS. Would like to know the thought of retrive 2nd line below the patten line too .. just came up ... Thanks.

 

[PHV]

Your solution may choke on huge input file (memory exhausted)
My solution stores only 3 lines of data.

BTW, NR%3 stands for NR modulo 3.

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886

 

[frankli]

Thanks a lot!

Regards,
-frank

 

[frankli]

following above thought I want to print the 2nd line below the pattern line but I can only pick up the 1st match line not all of them ... something is wrong please comment,

abc
def
ghi
jkl
mno
pqr
stu
abc
vwx
yza

use abc to print ghi, yza,

but I only get ghi use below ...

awk '{a[NR]=$0} /abc/ {b[NR]=NR+2} END {for (i in b); {print a[b]}}' input/file

Thanks!

 

[frankli]

below will print all the match line for above case ... but can not handle the memory choking ...

awk '{a[NR]=$0} /abc/ {b[NR]=NR+2} END {for (i in b) if (i != null) {print a[b]}}' input/file

 

[Annihilannic]

How about:

awk '/abc/ { getline; getline; print }'

Or:

awk '/abc/ { found=NR } NR==found+2'

Annihilannic.

 

[frankli]

Thanks Annihilannic.

Just FYI, for the 2nd option, if there is more than one line above the pattern line it will give out wrong output,

Try it against below

123
456
abc
def
ghi
jkl
mno
pqr
stu
abc
vwx
yza

the output of "awk '/abc/ { found=NR } NR==found+2'" would be

456
ghi
yza

 

[PHV]

awk '/abc/ { found=NR } found && NR==found+2

Hope This Helps, PH.
FAQ219-2884
FAQ181-2886