File-Transfer Pipes and Filters

Contents: This is a supplement to Section 4.2 of the C-Kermit 7.0 Update Notes, containing information specific to Kermit 95 in Windows 95, Windows NT, and OS/2.

IMPORTANT WARNING: In Windows 95, any command used in a pipeline must NOT be a 16-bit program, such as SORT. If it is, K95 will hang and must be killed from the task list, and your system will need to be rebooted. This is a Microsoft bug, discussed in many spots in the K95 Bugs List. For this reason, examples are shown for UNIX rather than Windows 95, since in practice there are very few standard utilities that can be used in this way (but keep reading, because luckily some of the most useful ones, such as GZIP and GUNZIP, can be):

NOTE: Section 4.2.7, Pipes and Encryption, of the C-Kermit 7.0 Update Notes, should be read in light of the availability of built-in Kerberos authentication and encryption, added in 1.1.16. Encryption through pipes is not needed when Telnet encryption is available.

Platform Differences

The SEND /COMMAND, RECEIVE /COMMAND, GET /COMMAND, and ! (bang) methods may be used with Kermit protocol transfers in all K95 versions with the cautions and restrictions noted in this section.

Since Windows 95, Windows NT, and OS/2 each support a wide range of application types (DOS 16-bit, DOS 32-bit, Windows 16-bit, Windows 32-bit, OS/2 16-bit, and OS/2 32-bit) it is important to be aware of the ways that each operating environment supports them. In all situations, K95 can pipe data only to or from other applications that use Standard Input and Standard Ouput (Stdin/Stdout). In most cases this means only Console applications, not GUI ones.

Windows 95

Windows 95 relies on its shell, COMMAND.COM, or a replacement such as 4DOS.COM, to form intermediary pipe connections between processes, but these pipes are implemented as temporary files. Thus each process in a pipeline runs to completion, writing a (possibly huge) file to disk before the next process starts. This means your disk can fill up, or that it could take a very long time for file transfer to start, because all the processes in the pipe must complete first.

While it is possible to mix and match DOS and Win32 console applications, we recommend sticking with 32-bit applications when piping data to/from Kermit-95, since mixing a 16-bit application with a 32-bit application requires running the 16-bit application under CONAGENT.EXE, which has numerous dangerous bugs, some acknowledged and documented by Microsoft, others not.

Windows NT

Windows NT supports DOS, Win32, and 16-bit OS/2 applications. All may be used to pipe data successfully to/from Kermit 95 without difficulties.


OS/2 supports DOS applications and 16-bit and 32-bit OS/2 applications. It is not possible to pipe data to/from a DOS application from/to Kermit-95 in OS/2; DOS applications run in a different session type than OS/2 applications and are not accessible to Kermit 95 through pipes. However, both 16-bit and 32-bit OS/2 applications may be mixed freely.

Applications for Use with Pipes

None of the operating systems that Kermit-95 runs on come with the strong set of command line utilities (filters) that we see on UNIX systems. However, many of the traditional UNIX filters are available as ports of the Free Software Foundation's GNU Project or as products of third-party companies.

Note, however, that the FSF does not support PC operating systems such as Windows, DOS, and OS/2, nor did it sanction adaptation of its utilities to these platforms. The GNU utilities for DOS, Windows, and OS/2 are available from non-FSF sites.

GNU Software

Third parties have ported many of the FSF GNU Project filter-like programs to Windows 95, Windows NT, and OS/2, including cat, cksum, comm, csplit, cut, expand, fmt, fold, head, join, md5sum, nl, od, paste, pr, sort, split, sum, tac, tail, tr, unexpand, uniq, wc, gzip, gunzip, gawk, and sed.

NOTE (2011): All the sites mentioned below have disappeared

Windows 95 and NT versions can be found at the popular Windows ftp sites, such as and The OS/2 versions, from Kai Uwe Rommel, can be found at:

These implementations are freely available on the Internet but might have some problems. For example, "creceive cat > filename" on Windows 95 or NT results in an incorrect error stating that the input and output pipes are the same (using cat version 1.6).

Gzip/Gunzip (GNU ZIP and UNZIP) archiving and compression software for Windows 95 and NT is available from:

And for OS/2 from:

Unlike the Info-Zip tools (Section, this package was designed from the beginning to handle pipes. So using Gzip and Gunzip on Windows 95, Windows NT, or OS/2, along with GNU or Hamilton tar, you may:

  Machine One: CSEND {tar cf - . | gzip} {archive.tgz} 
  Machine Two: CRECEIVE {gzip -d | tar xf -}


  CSEND {tar cf - . | gzip} {!gzip -d | tar xf -}

This should work between K95 (any platform) and K95, or between K95 (any platform) and UNIX or VMS that have gzip/gunzip installed, with the cautions noted in section 5.10.6 for cross-platform archive transfers.

Note: As of GZIP version 1.2.4, there are various bugs in these programs: the same crashing bug as noted for Info-ZIP zip/unzip (see, plus a failure of the OS/2 version to open pipes in binary mode (depending on which compiler it was built with), thus corrupting the ZIP format, rendering the result useless. These bugs have been reported to the maintainers, along with fixes, and hopefully new releases of these programs will be issued shortly.

The Hamilton C Shell

One source of high-quality filters that have been tested successfully with K95's pipes is from Hamilton Laboratories, Inc:

The Hamilton C Shell package includes a version of the Berkeley UNIX C-Shell for Windows 95, Windows NT (i386, alpha, mips, and ppc), and OS/2, and comes with an extensive array of UNIX filters and utilities, including all that you would expect to find in UNIX and many original additions, including a DES encryption filter. Using this filter we could support the following syntax for encrypted file transfers across the Internet:

  CSEND des -e -k < filename   

or, more ambitiously, an entire directory tree archived, compressed, and encrypted:

  CSEND {tar cf - . | gzip -c | des -e -k key} -
        {!des -d -k key | gunzip -c | tar xf -}

But here we have the same problem regarding transmission of keys we discussed elsewhere: the encryption key must be included on the command line or the user is prompted for it.

By the way, the Hamilton version of tar also supports Windows NT tape drives, which could be used for remote backups to tape.

Info-ZIP Utilities

The Info-ZIP project writes portable Zip/Unzip software for many platforms. More info at:

Ideally, it should be possible to use the Info-ZIP utilities to send an entire directory tree from one machine to another in compressed form. (NOTE: See Section 4.11 of the C-Kermit 7.0 Update Notes for another method of sending directory trees that does not depend on external utilities like ZIP.) This would provide better compression than found in modems and it would also provide compression over network connections where compression normally does not take place. And it would allow the data to be sent encrypted and confer other benefits as well.

But it turns out that although the Info-ZIP ZIP program has no problem creating a ZIP archive to Stdout ("zip - filelist") and can even compress Stdin to Stdout ("zip") or read the filelist to be compressed from Stdin and output the archive to Stdout ("zip -@ -"), the UNZIP program can't handle an archive as input from Stdin (this feature is on the list for version 6).

However, an FUNZIP (unzip filter) program is also provided as part of the Info-Zip package. But it has some major limitations. First, it can only output to Stdout. Second, it will only extract the first entry in an archive. This means that it is possible to do the following (be sure to use binary mode):

  Machine One:  CSEND {tar ... | zip} {} 
  Machine Two:  CRECEIVE {funzip | tar ...}

The output from tar is stored as the first entry in the archive under the name "-", which is extracted on Machine Two and fed to 'tar'. So you might as well use Gzip/Gunzip instead of zip/unzip in this situation.

Also, it should be noted that it is not possible to use encryption with the Info-Zip utilities when used as above since the password(s) must be issued interactively.

Finally, note that there is a bug in all versions of Unzip and Funzip up to 5.20 that can result in either memory exceptions or incorrect "invalid archive" errors. The bug has been reported, and a fix sent, to the maintainers, and the fix is available in version Unzip 5.30. For versions prior to 5.30, the following workaround can be used with 4NT:

  CSEND {zip -9 ckc*.h > nul & cat & del} -
        {!cat > ; unzip > errors}

This syntax only gets around the pipe bug in Zip 2.1 for NT and the Funzip 5.2 pipe bug, but notice it uses Unzip instead of Funzip, so this notation allows entire directory trees to be sent. But you need to know the command separator used on the remote system which is not only shell-dependent but can usually be reconfigured by the user.

NOTE: As of this writing, Zip 2.2 and Unzip 5.32 are current.

Related Commands and Functions

Can one reverse the procedure described at the end of Section of the C-Kermit 7.0 Update Notes, thus providing a Telnet server for Windows 95, Windows NT, or OS/2 by telling Kermit 95 to "redirect command" (i.e. COMMAND.COM) or "redirect 4dos", etc? Not quite...

While it might be possible to set up an incoming TCP/IP or serial connection with Kermit-95 and then REDIRECT a shell (COMMAND.COM, CMD.EXE, 4DOS.COM, 4NT.EXE, 4OS2.EXE, . . .) we recommend against redirecting 16-bit DOS Shells (anything ending in .COM). In OS/2 it isn't even possible since Kermit and the shell run in separate environments. In Windows 95, the DOS Shell is tightly tied to the old DOS structures and the BIOS which are not entirely accessible when running within a 32-bit Console session, as Kermit 95 does. While DOS and 32-bit Console windows may look alike, they are very different underneath. REDIRECTing 32-bit shells such as CMD.EXE on NT or OS/2 and 4NT.EXE or 4OS2.EXE from JP Software appears to work, but still might behave unpredictably because they are not designed to be receiving their input from Standard Input but want to read keystrokes directly; thus Backspace, F-keys, arrow keys, Page Up, etc, could not work in any case.

Do not start processes with the REDIRECT command, or from a command started with the REDIRECT command, that do not read from Standard Input and write to Standard Output. If you do, you won't be able to communicate with them. You might not be able to shut them down even when sitting in front of the machine. Ctrl-Alt-Del might be the only way. (Unless of course you have a port of the Unix 'kill' command.)

Kermit-95 itself (in its present form) is a perfect example of a program you cannot normally execute with a REDIRECT command. Kermit-95 reads directly from the keyboard and writes directly to the screen buffers. HOWEVER... beginning in version 1.1.16, it can be forced to use stdio, and is therefore redirectable. The command-line switch is "-# 96" (see Section 12). If you are in a whimsical mood, try this on a PC that's connected to the Internet:

  1. Start K95.
  2. Tell it to "set host * 2000".
  3. Make a Telnet connection to it from somewhere else (say, UNIX).
  4. When the K-95> reappears, type "redirect k95.exe -#96".
  5. Go back to the Telnet client from step (3) and see what you can do.

Results are not guaranteed, except to be interesting.

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