GPG: create/verify detached signature for a file

# create a detached signature for a file
gpg --output test.txt.sig.asc --armor --detach-sig test.txt

# In the above command you have to enter the passphrase via your
# keyboar. Add the following options to pass your passphrase via
# the command line:
#
# --batch --passphrase 'your_passphrase'
#
# Use a desired key
# --default-key [email protected]
#
# use a special digest
# --digest-algo SHA256

# verify a detached signature for a file
gpg --verify test.txt.sig.asc test.txt