Várias maneiras:
# gather the password into $P
stty -echo; read P; stty echo;
for i in *.gpg; do echo $i >> ~/t; printf '%s' | gpg -d --batch --passphrase-fd 0 $i >> ~/t; done
# gather the password into $P
stty -echo; read P; stty echo;
for i in *.gpg; do echo $i >> ~/t; gpg -d --batch --passphrase "$P" $i >> ~/t; done
d=$(mktemp -d)
# gather the password into a file named 'p'
stty -echo; cat > "$d/p"; stty echo
for i in *.gpg; do echo $i >> ~/t; gpg -d --batch --passphrase-file "$d/p" 0 $i >> ~/t; done
rm -rf "$d"