There's really no need to do a separate match and substitution, just change the pattern that the substitution matches: 
s/^((?i:ORACLE_SID|ORACLE_HST_SID|ORACLE_HOME|SDP_HOME))(?==)/(my $lhs
+=$1) =~ tr:_:.:; $lhs/e for @envArray;

[download]
(update: corrected the missing parens, as per Roger_B's update)
Caution: Contents may have been coded under pressure.

In reply to Re^3: substitution in a string by Roy Johnson
in thread substitution in a string by s_gaurav1091

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