Shell Programming and Scripting

And can u pls expain simply how code is working ??

Thanks in advance

Yes.
It's an AWK script:

Code:

awk '...' var1=value [var2=value ... varn=value] inputfile(s)

var=value assigns a value to a variable var accessible inside the AWK code.
So id=123 is the desired id to be passed to the program.

Following the code logic we have:

1. Construct the logical record (r) by concatenating all the records seen so far:

record r -> if record is not empty: r ? -> add a record separator (RS, newline by default) and the current record ($0): r RS $0, else (record is empty, it's the first access -> assign the value of the current record: : $0
This is the meaning of the following expression:

Code:

{ r = r ? r RS $0 : $0 }

2. Check if the current record matches the pattern "cm:" followed by the value of the variable id (see above): $0 ~ "cm:" id. If the test returns true, auto increment the value of the variable f (f for flag, marker): { f++ }.

Code:

$0 ~ "cm:" id { f++ }

3. If the current record does not match the pattern ^[\t ] : the line does not begin with a blank character (tab or space), these are your E, D etc records, do the following:
- check if the value of the variable f in Boolean context returns true (is not an empty string or has a numeric value 0): if it's true (not 0, see 2. above), this logical record contains our id, so we print it: print r.
- reset the r and the f variables, we will initialize them after if needed.

Code:

!/^[\t ]/ {
  if (f) print r
  r = f = 0
  }

4. After reading the entire input check if we have something to print.
This is because of the build (r) -> set (f) -> check after (!/^[\t ]/) logic:
we print the previous when we reach the current. So without the END block we may miss the last one.

Code:

END {
  if (f) print r
  }

Hope this helps.

Thnks alot radoulov for ur detailed explanation

Thanks for the explanation