grep and replace - perl

Question

I wanted to grep a string at the first occurrence ONLY from a file (file.dat) and replace it by reading from another file (output). I have a file called "output" as an example contains "AAA T 0001"
#!/bin/bash
procdir=`pwd`
cat output | while read lin1 lin2 lin3
do
srt2=$(echo $lin1 $lin2 $lin3 | awk '{print $1,$2,$3}')
grep -m 1 $lin1 $procdir/file.dat | xargs -r0 perl -pi -e 's/$lin1/$srt2/g'
done
Basically what I wanted is: When ever a string "AAA" is grep'ed from the file "file.dat" at the first instance, I want to replace the second and third column next to "AAA" by "T 0001" but still keep the first column "AAA" as it is. Th above script basically does not work. Basically "$lin1" and $srt2 variables are not understood inside 's/$lin1/$srt2/g'
Example:
in my file.dat I have a row
AAA D ---- CITY COUNTRY
What I want is :
AAA T 0001 CITY COUNTRY
Any comments are very appreciated.

Answer 1

If you have output file like this:
$ cat output
AAA T 0001
Your file.dat file contains information like:
$ cat file.dat
AAA D ---- CITY COUNTRY
BBB C ---- CITY COUNTRY
AAA D ---- CITY COUNTRY
You can try something like this with awk:
$ awk '
NR==FNR {
a[$1]=$0
next
}
$1 in a {
printf "%s ", a[$1]
delete a[$1]
for (i=4;i<=NF;i++) {
printf "%s ", $i
}
print ""
next
}1' output file.dat
AAA T 0001 CITY COUNTRY
BBB C ---- CITY COUNTRY
AAA D ---- CITY COUNTRY

Answer 2

Say you place the string for which to search in $s and the string with which to replace in $r, wouldn't the following do?
perl -i -pe'
BEGIN { ($s,$r)=splice(#ARGV,0,2) }
$done ||= s/\Q$s/$r/;
' "$s" "$r" file.dat
(Replaces the first instance if present)

Answer 3

This will only change the first match in the file:
#!/bin/bash
procdir=`pwd`
while read line; do
set $line
sed '0,/'"$1"'/s/\([^ ]* \)\([^ ]* [^ ]*\)/\1'"$2 $3"'/' $procdir/file.dat
done < output
To change all matching lines:
sed '/'"$1"'/s/\([^ ]* \)\([^ ]* [^ ]*\)/\1'"$2 $3"'/' $procdir/file.dat