You don't show the code you use, so it's hard to say how your regular expression "returns" something.

Maybe you want to use ([^\n]+) instead of the (\S+)? But \n would be in the \s class, so your \S shouldn't capture a \n. Please show the actual code you use.

Apologies. I meant to convey that $1 would "return" "\n" as well, instead of the non-spaces before it.
The regex I'd be using is DIP\s+\S+\s+(\S+).*?\\n

Ah. Now I understand. You have a literal "\n", not a newline in your data, but you don't want to capture that. The easiest way is to restrict the character class to not include the backslash:

for (<DATA>) {
    print "Matched: $1\n"
        if /DIP\s+\S+\s+([^\\\s]+).*?\\n/;
    
};
__DATA__
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant\n RTDMA-63           4      
+BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP                MG\n
+2-2-010109          MEAPH\nEND
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant      \n RTDMA-63           4
+      BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP              
+  MG\n2-2-010109          MEAPH\nEND
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant hello world \n RTDMA-63     
+      4      BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP       
+         MG\n2-2-010109          MEAPH\nEND
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant\n RTDMA-63           4      
+BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP                MG\n
+2-2-010109          MEAPH\nEND
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The character class \S will not match any whitespace, but the character sequence "\n" (that is, backslash, followed by "n") is not whitespace.

While of course the correct solution is to use the correct regexp, any time you have a string which may or may not have an undesired newline at the end, chomp can fix the problem