Editing C shell (section)

== Influence ==
[[File:Hamilton C shell x64 on Windows 7.png|thumb|300px|right|64-bit [[Hamilton C shell]] on a [[Windows 7]] desktop]]
The C shell was extremely successful in introducing a large number of innovations including the [[C shell#History|history]] mechanism, [[C shell#Aliases|aliases]], [[C shell#Tilde notation|tilde notation]], interactive filename completion, an expression grammar built into the shell, and more, that have since been copied by other Unix shells.  But in contrast to [[Bourne shell|sh]], which has spawned a large number of independently developed clones, including [[KornShell|ksh]] and [[Bash (Unix shell)|bash]], only two csh [[Clone (computing)|clones]] are known.  (Since [[tcsh]] was based on the csh code originally written by Bill Joy, it is not considered a clone.)

In 1986, [[Allen Holub]] wrote ''On Command: Writing a Unix-Like Shell for [[MS-DOS]]'',<ref>
{{cite book
  | first = Allen
  | last = Holub
  | author-link = Allen Holub
  | date = 1986{{ndash}}1987
  | edition = Second
  | title = On Command: Writing a Unix-Like Shell for MS-DOS
  | publisher = M&T Books, Redwood City, CA
  | isbn = 0-934375-29-1}}
</ref> a book describing a program he had written called "SH" but which in fact copied the language design and features of csh, not sh.  Companion diskettes containing full source for SH and for a basic set of Unix-like utilities (cat, cp, grep, etc.) were available for $25 and $30, respectively, from the publisher.  The control structures, expression grammar, history mechanism and other features in Holub's SH were identical to those of the C shell.

In 1988, Hamilton Laboratories began shipping [[Hamilton C shell]] for [[OS/2]].<ref>{{cite journal
 |last         = Hamilton
 |first        = Douglas
 |title        = Hamilton C shell Announcement
 |journal      = IBM Personal Systems Developer
 |issue        = Summer 1989
 |pages        = 119–121
 |url          = http://hamiltonlabs.com/Archives/Hamilton-C-Shell-Announcement-Douglas-A-Hamilton-IBM-Personal-Systems-Developer-Summer-1989.pdf
 |access-date   = 11 July 2020
}}</ref> It included both a csh clone and a set of Unix-like utilities. In 1992, Hamilton C shell was released for [[Windows NT]].<ref name=HamiltonReleaseNotes>
{{cite web
  | title = Hamilton C shell for Windows Release Notes 5.2.g
  | last = Hamilton
  | first = Nicole
  | url = http://hamiltonlabs.com/ReleaseNotes.htm
  | publisher = Hamilton Laboratories, Redmond, WA
  | date = 5 March 2017
  | access-date = 3 April 2018
}}
</ref> The Windows version continues to be actively supported but the OS/2 version was discontinued in 2003.<ref name=HamiltonReleaseNotes/> An early 1990 quick reference<ref>{{cite book
 |title        = Hamilton C shell Quick Reference
 |publisher    = Hamilton Laboratories, Wayland, MA
 |date         = 1988{{ndash}}1990
 |url          = http://hamiltonlabs.com/Archives/1990-07-10-Hamilton-C-shell-Quick-Reference.pdf
 |access-date   = 11 July 2020
}}</ref> described the intent as "full compliance with the entire C shell language (except [[C shell#Job control|job control]])" but with improvements to the language design and adaptation to the differences between Unix and a PC.  The most important improvement was a [[Top-down parsing|top-down parser]] that allowed [[control structure]]s to be nested or piped, something the original C shell could not support, given its ad hoc parser.  Hamilton also added new language features including built-in and user-defined procedures, block-structured local variables and floating point arithmetic.  Adaptation to a PC included support for the filename and other conventions on a PC and the use of [[Thread (computer science)|threads]] instead of [[Fork (system call)|forks]] (which were not available under either OS/2 or Windows) to achieve [[Parallel computing|parallelism]], e.g., in setting up a pipeline.