Sign a file with a given private key

sign.sh

#!/bin/bash
# Sign a file using the specified private key

# Source file to sign
SRCF=$1

# Private key location
PRIK=$2

# Signature algorithm (defaults to SHA-512)
ALGO=${3:-sha512}

# Algo file
ALGF=$SRCF.$ALGO.sig

# Prevent overwrite
if [ -f "$ALGF" ]; then
	echo "Signature file already exists"
	exit
fi

if [ -f "$PRIK" ]; then
	if [ -f "$SRCF" ]; then
		openssl dgst -$ALGO -sign $PRIK -out $ALGF $SRCF
	else
		echo "Source file not found"
	fi
else
	echo "Private key not found"
fi

exit

# To use this, run:
# sh sign.sh /path/to/file.ext /path/to/privatekey.pem

# A signature file will be created in "file.ext.sha512.sig" format

# To use a different algorithm E.G. SHA-256:
# sh sign.sh /path/to/file.ext /path/to/privatekey.pem sha356