How do I pass a variable into sftp?

Question

I'm trying to match a filename to a string, which is basically a timestamp, during an SFTP connection.

How do I match part of the filename? I can't seem to declare a variable within an SFTP connection. And neither can I call a variable created in Bash beforehand.

Edit: things I've tried

yr=$(date + "%Y")
sftp -i key.pem un@server
sftp> echo $yr
Invalid command.
sftp> $yr
Invalid command.

new shell

sftp -i key.pem un@server
sftp> test=$(date +"%Y")
Invalid command.

Tried those 2

Solution 1

The sftp program is its own thing; it's completely independent from and unrelated to bash, which knows the value of its variables and would expand $yr. In general, you can't pass bash variables into external programs like that without application-specific communication methods.

If you just want to upload or download a file with $yr in the filename, you could use scp instead, something like:

yr=$(date +%Y)
scp -i key.pem un@server:/some/long/path/that/includes/$yr .

for download, or

scp -i key.pem some_local_file un@server:/some/long/$yr/path

for upload.

If for some reason you really require using sftp specifically, you could create a batch file dynamically, e.g.

sftp -i key.pem -b - un@server <<< "get /some/path/with/$yr"

Solution 2

sftp is a standalone program, not a part of the shell. It doesn't understand shell syntax. It doesn't have features such as variable expansion and conditional statements.

The easiest way to do complex things over SFTP is to use SSHFS. SSHFS is a filesystem that uses SFTP to make a remote filesystem appear as a local filessytem. On the client, SSHFS requires FUSE, which is available on most modern unices. On the server, SSHFS requires SFTP; if the server allows SFTP then you can use SSHFS with it.

mkdir server
sshfs -o IdentityFile=key.pem un@server: server
cp "server/dir/myfile-$(date +%Y).txt" /local/path
fusermount -u server

Comments

[dhag]

Hi! It would be helpful if you edited your question to show the exact command you are using, so we can tell what you tried and what, precisely, doesn't work.

[Ed Heal]

SFTP is a protocol. Can be used in various ways

[simplycoding]

added in code of what I tried

[Ed Heal]

Use expect - that should do the business for you

[simplycoding]

If I use expect, I need to probably do a bunch of expect and send lines, right? Or can I just use expect once for the timestamp?

[simplycoding]

Yeah I looked into scp but it's not allowed on the server. I'm looking into expect at the moment

[Tom Hunt]

expect can do a lot, but it's fundamentally a hack used to allow scripting of programs which aren't designed to be scriptable. If you can use a different method, e.g. the -b option to sftp, it's usually easier. (Parenthetically, how is your server set up, that sftp is allowed but scp isn't?)

[simplycoding]

It's not my server, but all I know at the moment is that scp isn't allowed. Could you explain aht -b would do? Looking at documenation, its effect is that it notifies when jobs running in background terminate

[simplycoding]

Should I be able to set a variable in a here-doc? Or would that throw the same error as before?

[Tom Hunt]

You can expand variables in either heredocs or herestrings (herestring is the syntax I used above).