5 ms·

The single most useful thing about ssh to me is that it connects stdout/in across the channel (this is behavior inherited from rsh). This allows for e.g.: %

by jfb 13y ago

The single most useful thing about ssh to me is that it connects stdout/in across the channel (this is behavior inherited from rsh). This allows for e.g.: % (cd /foo; tar cpf - .) | ssh bar $cd /baz\; tar xpf -$ Or: % cat ~/.ssh/id_rsa.pub | ssh bar tee -a .ssh/authorized_keys

sopooneo 13y ago
Forgive my ignorance, but I don't know what what it means to connect "across the channel", but it sounds important. Do you know a link that explains the concept? I've failed to Google it.
- AYBABTME 13y ago
  What you pipe into ssh gets out of ssh on the host you're connected to. So basically, you get : (local) (remote) stdin -> ssh ssh -> stdout Hope that helps.
- greyfade 13y ago
  He's talking about forwarding stdin and stdout across the SSH connection to the program that SSH is running on the other end; such that the stdin of ssh is passed unmodified to the program and vice-versa.
- arnsholt 13y ago
  It means that whatever you put into the ssh process's STDIN gets sent to the STDIN of the remote process. For example you can do this: tar cj $bigdir | ssh host 'tar xj' That creates a tar.bz2 archive on your machine, sends it over ssh to the remote host, where it's unpacked. Ad hoc compressed and encrypted file transfers made easy.
  - mturmon 13y ago
    That's a good illustration, but rsync, if available, would generally be preferred for that use case: rsync -az $bigdir host:$bigdir
    - jfb 13y ago
      Sure, of course. But I've used that tar|ssh combination so much that it was the first example of using the rsh-like stdout/in pairing that came to mind. As much as I bitch about Unix and POSIX and horrific shell brain damage, I still reach for crazy shell pipelines when I have data manipulation tasks up to some pretty large scale n.
- jfb 13y ago
  Are you familiar with stdin/stdout/stderr on Unix and how they interact? What ssh does that I find so powerful is ensure that what you put into stdout on one side of a pipe flows out of stdin on the process that ssh starts on the remote host. Of course, ssh also gives you the output of the remote process, so you can put an ssh command in the middle of a pipeline. My day to day life no longer involves interacting with lots of remote Unix systems, but when it did, it was really, really useful.
dmckeon 13y ago
This is a bit of a pet peeve of mine, but cd/tar should likely be joined with && - in other words, in what directory do you want tar to (not) run if cd fails? So consider: % (cd /foo && tar cpf - .) | ssh bar '(cd /baz && tar xpf -)' or explore something like: % rsync -aSHx --update --delete -e ssh /foo/ user@bar:baz/.
- webreac 13y ago
  GNU tar has evolved and can use simpler syntax: % tar cp -C /foo . | ssh bar tar xp -C /baz
  - jfb 13y ago
    It would be an interesting project to look at people's shell usage and try to determine when they started using Unix. I have loads of Irixisms that have only recently been crowded out of my head by Darwin BSDism.
0x45696e6172 13y ago
ssh-copy-id is made for exactly this: ssh-copy-id - install your public key in a remote machine’s authorized_keys
- willthames 13y ago
  the tip does work on OS X though, which doesn't have ssh-copy-id (by default, at least)

by jfb 13y ago

sopooneo 13y ago

Forgive my ignorance, but I don't know what what it means to connect "across the channel", but it sounds important. Do you know a link that explains the concept? I've failed to Google it.

AYBABTME 13y ago
What you pipe into ssh gets out of ssh on the host you're connected to. So basically, you get : (local) (remote) stdin -> ssh ssh -> stdout Hope that helps.
greyfade 13y ago
He's talking about forwarding stdin and stdout across the SSH connection to the program that SSH is running on the other end; such that the stdin of ssh is passed unmodified to the program and vice-versa.
arnsholt 13y ago
It means that whatever you put into the ssh process's STDIN gets sent to the STDIN of the remote process. For example you can do this: tar cj $bigdir | ssh host 'tar xj' That creates a tar.bz2 archive on your machine, sends it over ssh to the remote host, where it's unpacked. Ad hoc compressed and encrypted file transfers made easy.
- mturmon 13y ago
  That's a good illustration, but rsync, if available, would generally be preferred for that use case: rsync -az $bigdir host:$bigdir
  - jfb 13y ago
    Sure, of course. But I've used that tar|ssh combination so much that it was the first example of using the rsh-like stdout/in pairing that came to mind. As much as I bitch about Unix and POSIX and horrific shell brain damage, I still reach for crazy shell pipelines when I have data manipulation tasks up to some pretty large scale n.
jfb 13y ago
Are you familiar with stdin/stdout/stderr on Unix and how they interact? What ssh does that I find so powerful is ensure that what you put into stdout on one side of a pipe flows out of stdin on the process that ssh starts on the remote host. Of course, ssh also gives you the output of the remote process, so you can put an ssh command in the middle of a pipeline. My day to day life no longer involves interacting with lots of remote Unix systems, but when it did, it was really, really useful.

dmckeon 13y ago

This is a bit of a pet peeve of mine, but cd/tar should likely be joined with && - in other words, in what directory do you want tar to (not) run if cd fails? So consider: % (cd /foo && tar cpf - .) | ssh bar '(cd /baz && tar xpf -)' or explore something like: % rsync -aSHx --update --delete -e ssh /foo/ user@bar:baz/.

webreac 13y ago
GNU tar has evolved and can use simpler syntax: % tar cp -C /foo . | ssh bar tar xp -C /baz
- jfb 13y ago
  It would be an interesting project to look at people's shell usage and try to determine when they started using Unix. I have loads of Irixisms that have only recently been crowded out of my head by Darwin BSDism.

0x45696e6172 13y ago

ssh-copy-id is made for exactly this: ssh-copy-id - install your public key in a remote machine’s authorized_keys

willthames 13y ago
the tip does work on OS X though, which doesn't have ssh-copy-id (by default, at least)