The following is a decent solution across Unix/Linux installations, that does not rely on any unusual program features. This supports a multi-line message body, multiple attachments, and all the other typical features of mailx.
Unfortunately, it does not fit on a single line.
#!/bin/ksh
# Get the date stamp for temporary files
DT_STAMP=`date +'%C%y%m%d%H%M%S'`
# Create a multi-line body
echo "here you put the message body
which can be split across multiple lines!
woohoo!
" > body-${DT_STAMP}.mail
# Add several attachments
uuencode File1.pdf File1.pdf > attachments-${DT_STAMP}.mail
uuencode File2.pdf File2.pdf >> attachments-${DT_STAMP}.mail
# Put everything together and send it off!
cat body-${DT_STAMP}.mail attachments-${DT_STAMP}.mail > out-${DT_STAMP}.mail
mailx -s "here you put the message subject" nobody@test-address.com < out-${DT_STAMP}.mail
# Clean up temporary files
rm body-${DT_STAMP}.mail
rm attachments-${DT_STAMP}.mail
rm out-${DT_STAMP}.mail
