Output text between two PATTERNS if text matches a CRITERIA

Question

I want to select blocks between PATTERN1 and PATTERN2 if text inside the block contains CRITERIA, otherwise discard the whole block.

Sample task: Select text between PATTERN1='start' and PATTERN2='end', if some text between 'start' and 'end' matches CRITERIA='DCE', then output the whole block between 'start' and 'end'.

Sample input:

start
123
ABC
123
end
start
123
DCE
123
end
start
123
EFG
123
end

Sample output:

start
123
DCE
123
end

I've tried the following using awk, but couldn't find how to use CRITERIA between two patterns:

awk '/start/,/end/' input_file

Answer 1

EDIT: As per OP a Input_file may have match at the end too and may not have end string, so adding code as per that too now.

awk '
/start/{
  if(val)               {   print value   };
  flag=1;
  value=val=""}
/[dD[cC][eE]/ && flag   {   val=1         }
/end/                   {   flag=""       }
flag{
  value=value?value ORS $0:$0
}
END{
  if(val)               {   print value   }}
'  Input_file

Explanation:

awk '
/start/{                                     ##Looking for string start in a line if found then do following.
  if(val)               {   print value   }; ##Checking if variable val is NOT NULL, if yes then print variable of value.
  flag=1;                                    ##Setting variable named flag as 1 here.
  value=val=""}                              ##Nullifying variables value and val here.
/[dD[cC][eE]/ && flag   {   val=1         }  ##Searching string DCE/dce in a line and checking if variable flag is NOT NULL then set variable val as 1.
/end/                   {   flag=""       }  ##Searching string end in current line, if found then Nullifying flag here.
flag{                                        ##Checking if variable named flag is SET or NOT NULL here.
  value=value?value ORS $0:$0                ##Creating value whose value is current line value and concatenating in its own value.
}
END{                                         ##Starting END block of awk here.
  if(val)               {   print value   }} ##Checking if variable val is NOT NULL then print variable value here.
'  Input_file

---

Could you please try following awk and let me know if this helps you.

awk '/start/{if(val){print value};flag=1;value=val=""} /[dD[cC][eE]/ && flag{val=1} /end/{flag=""} {value=value?value ORS $0:$0}' Input_file

Adding a non-one liner form of solution too here.

awk '
/start/{
  if(val)            { print value  };
  flag=1;
  value=val=""}
/[dD[cC][eE]/ && flag{  val=1       }
/end/                {  flag=""     }
{
  value=value?value ORS $0:$0
}
'   Input_file