This looks like a job for Range Operators: 
use strict;
use warnings;

while (<DATA>) {
    print if (/BEGIN RSA PRIVATE KEY/ .. /END RSA PRIVATE KEY/);
}

__DATA__
Bag Attributes
    localKeyID: 33 32 34 33 39 38 33 33 30 32 36 30 33 
    friendlyName: verisign class 3 public primary certification author
+ity
subject=/C=US/O=VeriSign, Inc./OU=Class 3 Public Primary Certification
+ Authority
issuer=/C=US/O=VeriSign, Inc./OU=Class 3 Public Primary Certification 
+Authority
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
Bag Attributes
    localKeyID: 31 32 33 33 39 38 33 33 30 22 11 30 34 
    friendlyName: mycerts.test.com
Key Attributes: <No Attributes>
-----BEGIN RSA PRIVATE KEY-----
THIS IS THE FILE i WANT
...
-----END RSA PRIVATE KEY-----
Bag Attributes
    localKeyID: 23 32 34 33 39 38 33 33 44 32 36 30 21 
    friendlyName: mycerts.test.com
subject=/C=US/ST=Somewhere/L=There/O=My Org/OU=Terms of use at www.ver
+isign.com/rpa (c)00/CN=MYCERTS.TEST.COM
issuer=/O=VeriSign Trust Network/OU=VeriSign, Inc./OU=VeriSign Interna
+tional Server CA - Class 3/OU=www.verisign.com/CPS Incorp.by Ref. LIA
+BILITY LTD.(c)97 VeriSign
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----
Bag Attributes
    localKeyID: 31 32 34 33 39 38 44 33 30 32 36 30 36 
    friendlyName: verisign intermediate ca
subject=/O=VeriSign Trust Network/OU=VeriSign, Inc./OU=VeriSign Intern
+ational Server CA - Class 3/OU=www.verisign.com/CPS Incorp.by Ref. LI
+ABILITY LTD.(c)97 VeriSign
issuer=/C=US/O=VeriSign, Inc./OU=Class 3 Public Primary Certification 
+Authority
-----BEGIN CERTIFICATE-----
...
-----END CERTIFICATE-----

[download]

which prints: 

-----BEGIN RSA PRIVATE KEY-----
THIS IS THE FILE i WANT
...
-----END RSA PRIVATE KEY-----

[download]

In reply to Re: Using Perl to convert pkcs12 certificates to pem format, separate files for public/public keys by toolic
in thread Using Perl to convert pkcs12 certificates to pem format, separate files for public/public keys by symgryph

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