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Secure Shell and SCP Support
Besides recognizing ftp:// URLs as described in the previous section,
Epsilon also recognizes scp:// URLs, which may be used for secure file
transfers. With scp support, you can read or write files using an
scp:// URL, navigate the remote system's directory tree using dired,
mark files for copying between the local and remote systems, use
grep or file-query-replace to search and replace on
multiple remote files, and use file name completion.
Epsilon also recognizes ssh:// URLs to connect securely to a command
shell on a remote computer, providing a secure alternative to the
telnet command. Epsilon's ssh command works similarly
to the ssh:// URL. Use the syntax username@hostname to connect as
a user other than the default one. The ssh-interpret-output
variable controls how Epsilon interprets ANSI escape sequences and
similar in an ssh buffer.
The scp and ssh features work by running certain external programs
which must be installed. Epsilon's ssh command depends on an
external ssh program, while its scp features run a program named
sftp . On Mac OS these are normally preinstalled. For Linux or
FreeBSD, you may need to install the appropriate ssh package for your
distribution. For Windows, the Cygwin system contains appropriate
clients. Run the Cygwin installer from the Cygwin website
http://www.cygwin.com and install Cygwin's openssh package from
the net section. Also ensure Cygwin's bin directory is on your PATH.
(On Windows, it's also possible to use alternative clients like PuTTY
instead of Cygwin programs. See "Windows-specific Configuration"
below for more on PuTTY.)
With scp/ssh support, Epsilon doesn't remember your
password or passphrase. Epsilon will ask for it each time it must
start a new sftp helper program (for instance, when you begin a
second file operation before the first has completed). If you prefer
to type your secure passphrase once and have multiple connections use
it, you can set up an ssh-agent program, along with public key
authentication. The agent will remember your credentials and provide
them as required to any sftp or ssh instance. You can even set your
credentials to expire after a certain period of time if you wish.
Refer to the manual page for the ssh-agent program to set this up.
Windows users should also see the section below on Windows-specific
configuration.
Customization Options for Alternative Clients
If you're not using the usual external ssh and sftp programs,
you'll need to set various variables to tell Epsilon how to run your
alternative programs.
The variable ssh-template tells Epsilon how to build a command
line for invoking the external ssh program when a specific user name
appears before the host name. If no user name was specified, it uses
ssh-no-user-template. See the descriptions of these variables
for their format. There are also numerous variables whose names start
with sftp- that may be used to configure Epsilon to work with
alternatives to the sftp program.
Some very old sftp programs use a different command syntax for listing
files; if you have trouble, try setting the scp-client-style
variable to 2 to make Epsilon use old-style sftp commands. You
may have to modify scp-list-flags too.
Windows-specific Configuration Options
As explained above, using an ssh-agent program along with public key authentication
lets you type your secure passphrase once and have multiple
connections use it. The agent must provide some settings that are
passed on to the sftp or ssh clients it runs via environment
variables. For Windows users running Cygwin, one option is to start
Cygwin's bash shell, run the command eval `ssh-agent` , run the
ssh-add command, and then run Epsilon from that same shell. Or
you can use the run-ssh-agent.bat file included in Epsilon's bin
subdirectory to run an ssh agent. The comments in that file explain
how to run ssh-agent through it, so it creates a load-ssh-agent batch
file that loads agent settings into the environment, and how to set
Epsilon variables so Epsilon invokes load-ssh-agent when starting ssh
or scp sessions.
To make Epsilon work with the Windows ssh client PuTTY instead of
the recommended Cygwin clients, use these settings:
| scp-windows-sftp-command | psftp |
| ssh-template | plink -l %u %h |
| ssh-no-user-template | plink %h |
| scp-client-style | 2 |
Be sure to install PuTTY's psftp and plink programs along with
the base PuTTY installation. With PuTTY, certain features like file name
completion won't be available.
Per-System Settings
It's possible to set up Epsilon to use one set of variables for one
remote system and a different one for others. To enable this, before
checking for a variable such as scp-run-helper-template, Epsilon
constructs a new variable name by adding the host name of the remote
system to its end. For instance, if you try to access
www.example.com, Epsilon first looks for a variable named
scp-run-helper-template-www-example-com ; if there's a variable by
that name, Epsilon uses it instead of the usual one. (Epsilon
constructs the variable name from a host name by replacing each
non-alphanumeric character with a -.) It does this for each of its
scp and ssh variables.
Using Ancient Hosts
If you must use a very old version of ssh that lacks an sftp program,
or connect to a system that doesn't support sftp, or you want to use
an ssh replacement that lacks sftp, it's possible to set up Epsilon to
run its own helper program on the remote system.
To do this, copy the C language source code file
epsilon-xfer-helper.c included in
Epsilon's source directory to the remote system, compile it with
"make epsilon-xfer-helper" or similar, and
install in an accessible location. It may be compiled on most Unix
systems, or, for Windows, using the Cygwin environment. Next, check
that you can run the helper program remotely, with a command line like
ssh -l username hostname epsilon-xfer-helper
It should print a greeting line and await a command. Type ^C or press
<Enter> to make it exit. You may need to edit the Epsilon
variable scp-run-helper-template to include the path to the
helper program, or if you use a different ssh program. For instance,
if you use an ssh client "oldssh" that lacks an sftp program, set it
to "oldssh %u@%h /path/to/epsilon-xfer-helper " or similar.
(Epsilon uses the above variable when the scp:// url includes a user
name, and the scp-run-helper-no-user-template variable when it
does not.)
To tell Epsilon to use epsilon-xfer-helper commands, not sftp
commands, set the scp-client-style variable to 1 . Using
the helper program enables a few minor features that the sftp program
doesn't currently support, like using ~ to indicate home
directories, or copying a remote file to a different location on the
remote system (sftp can rename remote files but not copy them).
When you don't use sftp, Epsilon must run a separate program for each
file transfer. By default it uses the scp program. The variable
scp-read-file-template tells Epsilon how to transfer a file from
the remote system to a local file, and scp-write-file-template
does the opposite. There are separate versions of these variables for
when no user name is included, named
scp-read-file-no-user-template and
scp-write-file-no-user-template. Change these variables to use
a different program for copying files when you don't use sftp.
Standard bindings:
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