This is a sample openssl bash script to create a matching RSA key pair and create a signed sha1 digest of the script itself using the private key. The digest is then verified against the public key.

OpenSSL Verify Signature in Bash

#!/bin/bash

#create our key pairs
openssl genrsa -out private.pem 2048
openssl rsa -in private.pem -pubout -out public.pem

#sign and verify
openssl dgst -sha1 -sign private.pem -out "$0".sha1 $0
openssl dgst -sha1 -verify public.pem -signature "$0".sha1 $0

#purposely not cleaning up after the program.