Ruby

Duplicate openssl pkey -in private.pem -pubout -out pubkey.pem

See more OpenSSL Examples

How to output the public part of a private key: Demonstrates how to duplicate this OpenSSL command:

openssl pkey -in private.pem -pubout -out pubkey.pem

Ruby

require 'chilkat'

success = false

pkey = Chilkat::CkPrivateKey.new()

# Load the private key from an PEM file:
success = pkey.LoadPemFile("private.pem")
if (success == false)
    print pkey.lastErrorText() + "\n";
    exit
end

pubKey = Chilkat::CkPublicKey.new()
pkey.ToPublicKey(pubKey)

success = pubKey.SavePemFile(false,"pubKey.pem")
if (success != true)
    print pubKey.lastErrorText() + "\n";

    exit
end

print "Success." + "\n";