A (Bash) shell function for creating digest values.

hash_hmac.sh

#!/bin/sh --

function hash_hmac {
  digest="$1"
  data="$2"
  key="$3"
  shift 3
  echo -n "$data" | openssl dgst "-$digest" -hmac "$key" "$@"
}

# hex output by default
hash_hmac sha1 'value' 'key'

# raw output by adding the "-binary" flag
hash_hmac sha1 'value' 'key' -binary | base64

# other algos also work
hash_hmac md5 'value' 'key'