ssh-vault can read from standard input (stdin) when creating a vault.

Instead of creating a vault from scratch, a vault can be created by using an existing file, for example if Alice wants to send a file (txt, pdf, jpg) to Bob she could so something like:

ssh-vault -u bob create < /path/to/file > bobs.vault

or

cat /path/to/file | ssh-vault -u bob create bobs.vault

To restore the file for example my.pdf:

ssh-vault -o /path/to/my.pdf view bobs.vault

you can choose any name you want for the vault, in this example the vault contents will be written to file bobs.vault

on the fly

In case you just want to send a simple string/password this can be used:

echo "secret" | ssh-vault -u bob create

notice that no vault was defined this means that output will be STDOUT

On a mac you could do this one-liner in order to have the output on the clipboard:

echo "secret" | ssh-vault -u bob create | pbcopy

view stdin

If some one send you a vault you can pass directly to ssh-vault and view it:

echo "SSH-VAULT;AES256;24:c6:6f:33:49:de:d7:bb:77:cf:e9:78:4c:e9:25:5f
e4DHrRQlnv+KWzYipQUyu3xeOM5c1OmezgQaiIoEgEA2FlaK0YHYhOmj66hBa0SF
yohpe9Y1F8HoVavpy2WgUWx+nJE+2Zj6UK4cU0FYhVdjs733rFaicUOW87LIsy9H
r+2l+cGdGoboH/jw/asXegSccVhHSWHKyi0mvAuoh4yaEUpM9iYlQhfG75ABQh4k
pFgJc++1QL/TCV/Hz8dzrfPzv9Xy57HEwnGKyx0grzFoV9pKVt2bS2BMPNQIZFlc
j98aIMf6rPz8vmugjaxAeBDNHViwfr0I2cIw5n7qrgQXpFrcHiVgBJDtE9ck7EMO
jNf3Y8QCYPBnLOVKCNwwIA==;Bnvo5I7XJWAKSeVV6i69PyGwMU7FznSAX5VqLQj
o" | ssh-vault view

So for testing only purposes when using same key this should work (if ssh-key has no password):

echo "secret" | ssh-vault -u bob create | ssh-vault view