If the FOREIGN KEY statement always follows immediately behind the fk table, and the fk table only shows up once in the sql string (i.e. if your sql string always looks like the above), you can simply do:

use strict;
my $sql='"ALTER TABLE "ARSAMS"."TCMD_HEADER" ADD CONSTRAINT FK_TCMD_HE
+A_OWNER_CONTAINE (CONTAINER_OWNER_CD) REFERENCES ARSAMS.CONTAINER_OWN
+ER_CODE (CONTAINER_OWNER_CD)"';
my $fk_table_name="FK_TCMD_HEA_OWNER_CONTAINE";
$sql=~s/($fk_table_name)/$1 FOREIGN KEY/;
print $sql;
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CU
Robartes-