Replacing first and second occurrence of the same text with different values

I'm searching for a way to replace the first occurrence of a certain text in a text file with a value ${A} and the second occurrence of the same text, on a different line, with ${B}. Can this be achieved with sed or awk or any other UNIX tool?

The toolset is fairly limited: bash, common UNIX tools like sed, grep, awk etc. Perl, Python, Ruby etc. cannot be used...

Thanks in advance for any advice Robert

Example:

...
Text
Text
Text
Text
TEXT_TO_BE_REPLACED
Text
Text
Text
TEXT_TO_BE_REPLACED
Text
Text
Text
...

should be replaced with

...
Text
Text
Text
Text
REPLACEMENT_TEXT_A
Text
Text
Text
REPLACEMENT_TEXT_B
Text
Text
Text
...

Sed with one run:

sed -e 's/\(TEXT_TO_BE_REPLACED\)/REPLACEMENT_TEXT_A/1' \
    -e 's/\(TEXT_TO_BE_REPLACED\)/REPLACEMENT_B/1' < input_file > output_file

Just run your script twice - once to replace the first occurrence with ${A}, once to replace the (now first) occurence with ${B}. To replace just one occurence:

sed '0,/RE/s//to_that/' file

(shamelessly stolen from How to use sed to replace only the first occurrence in a file?)

Here is a possible solution using awk:

#!/usr/bin/awk -f

/TEXT_TO_BE_REPLACED/ {
   if ( n == 0 ) {
      sub( /TEXT_TO_BE_REPLACED/, "REPLACEMENT_TEXT_A", $0 );
      n++;
   }
   else if ( n == 1 ) {
      sub( /TEXT_TO_BE_REPLACED/, "REPLACEMENT_TEXT_B", $0 );
      n++;
   }
}

{
   print
}

awk 'BEGIN { a[0]="REPLACEMENT_A"; a[1]="REPLACEMENT_B"; } \
  /TEXT_TO_BE_REPLACED/ { gsub( "TEXT_TO_BE_REPLACED", a[i++]); i%=2 }; 1'

So, you can use sed to do this like so:

First, I made a file named test.txt that contained:

well here is an example text example
and here is another example text

I choose to use the word "example" to be the value to change.

Here is the command: cat test.txt | sed -e 's/(example)/test2/2' -e 's/(example)/test1/1'

which provides the following output:

well here is an test1 text test2
and here is another test1 text

Now the sed command broken down:

s - begins search + replace 
/ - start search ended with another /
The parentheses group our text ie example
/test2/ what we are putting in place of example
The number after the slashes is the occurrence we want to replace. 

the -e allows you to run both commands on one command line.

You may also use the text editor ed:

# cf. http://wiki.bash-hackers.org/howto/edit-ed
cat <<-'EOF' | sed -e 's/^ *//' -e 's/ *$//' | ed -s file
   H
   /TEXT_TO_BE_REPLACED/s//REPLACEMENT_TEXT_A/
   /TEXT_TO_BE_REPLACED/s//REPLACEMENT_TEXT_B/
   wq
EOF