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Epsilon User's Manual and Reference
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Internet Support  Commands by Topic   URL Syntax

Epsilon User's Manual and Reference > Commands by Topic > Buffers and Files > Internet Support >

Secure Shell and SCP Support

Besides recognizing ftp:// URLs, 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 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 scp and ssh features work by running certain external programs. Epsilon's ssh command depends on an external ssh program. With default settings, scp features use an sftp program, which is part of the ssh package. For Linux or FreeBSD, install the appropriate ssh package for your distribution.

For Windows, the Cygwin system contains appropriate clients. Install Cygwin's openssh package from the net section, and ensure Cygwin's bin directory is on your PATH. Or with some configuration you can use alternatives like PuTTY. (See below for more on PuTTY.) With PuTTY, certain features like file name completion won't be available. Scp and ssh support works on Unix and under Windows NT/2000/XP/Vista, but not under Windows 95/98/ME.

With scp/ssh support, Epsilon doesn't remember your password or passphrase. Epsilon will ask for it each time it must start a new scp or sftp helper program; for instance, when you begin a second scp operation before the first has completed. You can use an ssh agent to manage your keys and passphrases (see the manual page for ssh-agent in your ssh distribution) to avoid having to type them more than once.

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. The ssh-interpret-output variable controls how Epsilon interprets ANSI escape sequences and similar in an ssh buffer.

Epsilon runs an sftp program to copy files, obtain file listings for dired, and do many miscellaneous tasks like create directories or perform completion. Some 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.

Hints for Windows

To make Epsilon work with the Windows ssh client PuTTY, 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.

If you want to run Cygwin's ssh-agent under Windows, one way 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 under Windows XP or Vista, 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 in your root directory 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.

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, 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 the scp and ssh variables mentioned above.

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:

 Ssh mode only: Alt-n  process-next-cmd
 Ssh mode only: Alt-p  process-previous-cmd

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