signing a text file:-

zodiac@zodioc:~$ gpg --clearsign myfile

You need a passphrase to unlock the secret key for
user: "Celsius Thomas (My work key) "
1024-bit DSA key, ID 56B304BA, created 2010-04-03

original file has this content:- hello world


Then the signed file will look something like this:-


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

hello world
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)

iEYEARECAAYFAku3WEgACgkQvEorF1azBLrqgQCePziUoHP6zspKJhSfZRT+Fxfs
X/AAnRUevcz5vZ94dI1lhVH7ubdEissR
=jQ5/
-----END PGP SIGNATURE-----


Anyone who has your public key can check the signature in this file using gpg , thereby confirming that the file is from you.