Print range of rows if a condition is met in AWK - linux

Question

What I am trying to do is to show 2 rows above and 2 rows below a line that meets a certain criteria without a pipe, using awk. For example, I am searching for the string 's62234' and when found, I want to print all the rows bounded in the blue rectangle as shown in the attached screenshot.
This is the file I am using (thefmifile.txt)
s62098:x:1271:504:Velizar Vrabchev,SI,3,1:/home/SI/s62098:/bin/bash
s62101:x:1272:504:Georgi Georgiev,SI,3,5:/home/SI/s62101:/bin/bash
s62108:x:1273:504:Sherif Kunch,SI,3,1:/home/SI/s62108:/bin/bash
s62111:x:1274:504:Yulian Bizeranov,SI,3,3:/home/SI/s62111:/bin/bash
s62121:x:1275:504:Daniel Dimitrov,SI,2,1:/home/SI/s62121:/bin/bash
s62133:x:1276:504:Ivaylo Ivanov,SI,2,2:/home/SI/s62133:/bin/bash
s62160:x:1277:504:Veniyana Tsolova,SI,2,3:/home/SI/s62160:/bin/bash
s62199:x:1278:504:Nikola Petrov,SI,2,5:/home/SI/s62199:/bin/bash
s62219:x:1279:504:Viliyan Ivanov,SI,2,6:/home/SI/s62219:/bin/bash
s62234:x:1280:504:Viktoriya Dobreva,SI,2,3:/home/SI/s62234:/bin/bash
s855264:x:1281:504:Toni Dupkarski,SI,4,2:/home/SI/s855264:/bin/bash
s81555:x:1282:503:Elena Georgieva,KN,2,0:/home/KN/s81555:/bin/bash
s81585:x:1283:503:Stela Marinova,KN,2,0:/home/KN/s81585:/bin/bash
s81441:x:1284:503:Vesela Plamenova Borislavova , KN, k2, g7:/home/KN/s81441:/bin/bash
s81644:x:1285:503:Viktor Rusev, KN, k2, g7:/home/KN/s81644:/bin/bash
s81628:x:1286:503:Iliyan Yordanov Yordanov, KN, k2, g6:/home/KN/s81628:/bin/bash
s81490:x:1287:503:Yana Spasova, KN, k2, g6:/home/KN/s81490:/bin/bash
What I have tried is using awk to find the row that meets the criteria and use NR to get the numbers of the other rows needed, but seems I am missing something.
Here is the command I used:
cat thefmifile.txt | awk -F ':' '$1==s62234 {for (x = NR -2; x <= NR + 2; x++){print}}'
Output is in the below screenshot.
And this is the desired output:
s62199:x:1278:504:Nikola Petrov,SI,2,5:/home/SI/s62199:/bin/bash
s62219:x:1279:504:Viliyan Ivanov,SI,2,6:/home/SI/s62219:/bin/bash
s62234:x:1280:504:Viktoriya Dobreva,SI,2,3:/home/SI/s62234:/bin/bash
s855264:x:1281:504:Toni Dupkarski,SI,4,2:/home/SI/s855264:/bin/bash
s81555:x:1282:503:Elena Georgieva,KN,2,0:/home/KN/s81555:/bin/bash
When it is {print x} it shows the numbers of the lines I need, but is there some way to access the lines of the file as elements in array and just to use this 'x' as an index (e.g. something like NR[x])?
Or Is there some other way to retrieve these rows?
Thank you!

Answer 1

$ awk -v n=2 -F':' '$1=="s62234"{for (i=0;i<n;i++) print buf[(NR+i)%n]; c=n+1} c&&c--; {buf[NR%n]=$0}' file
s62199:x:1278:504:Nikola Petrov,SI,2,5:/home/SI/s62199:/bin/bash
s62219:x:1279:504:Viliyan Ivanov,SI,2,6:/home/SI/s62219:/bin/bash
s62234:x:1280:504:Viktoriya Dobreva,SI,2,3:/home/SI/s62234:/bin/bash
s855264:x:1281:504:Toni Dupkarski,SI,4,2:/home/SI/s855264:/bin/bash
s81555:x:1282:503:Elena Georgieva,KN,2,0:/home/KN/s81555:/bin/bash
buf[] is just an array storing the n lines preceding the current line so those can be printed when your $1=="s62234" condition is met. c&&c--; represents a true condition which will cause awk to print (the default action) the current line plus n subsequent lines due to c=n+1 also being set when your condition is met - i.e. it'll print the current line and decrement c until c reaches zero.

Answer 2

Could you please try following, simple grep could handle this task.
grep -A2 -B2 '^s62234:' Input_file
Also more accurately you could try following to match exact string with grep:
grep -C2 '^s62234:' Input_file

Answer 3

That's easily doable with grep:
-B, --before-context=NUM print NUM lines of leading context
-A, --after-context=NUM print NUM lines of trailing context
-C, --context=NUM print NUM lines of output context
-NUM same as --context=NUM
With awk, you could do something like this:
awk -F ':' '$1==s62234{print l2;print l1;a=3}a&&a-->0{print}{l2=l1;l1=$0}' thefmifile.txt
You can handle the number of before-lines dynamically by storing them in an array and using a loop.