Reading your 'duplicate' post, I'm not quite sure what you are trying to achieve there. As to this post, the example below may be of interest. I think it should be suitable for either line-by-line or whole-file processing. 5.10+ needed due to use of  \K operator.

BTW: In addition to the problems with the code in this post pointed out by JavaFan, I would add that  int rand 9999 will only produce numbers in the range 0 .. 9998. I don't know if this was intended or not. 

>perl -wMstrict -le
"my $s =
   'xx @ra[1] y @ara[23] z @ra[1] aa @ara[23] b @ra[1] @ara[23]';
 print qq{'$s'};
 ;;
 my %found;
 $s =~ s{ \@ ([a-z] [a-z\d_]* \[) \K (\d+) (?= \]) }
        { $found{$1 . $2} //= int rand 9999;       }xmsge;
 print qq{'$s'};
"
'xx @ra[1] y @ara[23] z @ra[1] aa @ara[23] b @ra[1] @ara[23]'
'xx @ra[2038] y @ara[6310] z @ra[2038] aa @ara[6310] b @ra[2038] @ara[
+6310]'

[download]

Update: Used  //= instead of  ||= in substitution replacement block code per Anonymonk's usage below.

In reply to Re: Same problem replacing array index numbers by AnomalousMonk
in thread Same problem replacing array index numbers by astroid96

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