Hamilton C shell is a clone of the Unix C shell and

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Early for

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created by Nicole Hamilton at Hamilton Laboratories as a completely original work, not based on any prior code. It was first released on

OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 r ...

on December 12, 1988 and on

Windows NT Windows NT is a proprietary graphical operating system produced by Microsoft, the first version of which was released on July 27, 1993. It is a processor-independent, multiprocessing and multi-user operating system. The first version of Win ...

in July 1992. The OS/2 version was discontinued in 2003 but the Windows version continues to be actively supported.

Design

Hamilton C shell differs from the Unix C shell in several respects. These include its

compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...

architecture, its use of threads, and the decision to follow Windows rather than Unix conventions.

Parser

Hamilton C shell and Cygwin bash recursion

The original C shell uses an ad hoc parser. This has led to complaints about its limitations. It works well enough for the kinds of things users type interactively but not very well for the more complex commands a user might take time to write in a script. It is not possible, for example, to pipe the output of a foreach statement into

grep grep is a command-line utility for searching plain-text data sets for lines that match a regular expression. Its name comes from the ed command ''g/re/p'' (''globally search for a regular expression and print matching lines''), which has the sa ...

. There was a limit to how complex a command it could handle.''Csh Programming Considered Harmful''
by Tom Christiansen By contrast, Hamilton uses a top-down

recursive descent parser In computer science, a recursive descent parser is a kind of top-down parser built from a set of mutually recursive procedures (or a non-recursive equivalent) where each such procedure implements one of the nonterminals of the grammar. Thus t ...

that allows it to compile statements to an internal form before running them. As a result, statements can be nested or piped arbitrarily. The language has also been extended with built-in and user-defined procedures, local variables, floating point and additional expression, editing and wildcarding operators, including an "indefinite directory" wildcard construct written as "..." that matches zero or more directory levels as required to make the rest of the pattern match.

Threads

Hamilton C shell and Cygwin bash date loops

Lacking

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or a high performance way to recreate that functionality, Hamilton uses the Windows threads facilities instead. When a new thread is created, it runs within the same process space and it shares all of the process state. If one thread changes the current directory or the contents of memory, it's changed for all the threads. It's much cheaper to create a thread than a process but there's no isolation between them. To recreate the missing isolation of separate processes, the threads cooperate to share resources using

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Windows conventions

Hamilton differs from other Unix shells in that it also directly supports Windows conventions for drive letters, filename slashes,

escape character In computing and telecommunication, an escape character is a character (computing), character that invokes an alternative interpretation on the following characters in a character sequence. An escape character is a particular case of metacharac ...

s, etc.

References

External links

*
Hamilton C shell user guide
{{Unix shells Unix shells OS/2 command shells Windows command shells Scripting languages Unix text processing utilities Unix emulators Programming tools Programming tools for Windows Utilities for Windows 1988 software Programming languages created in 1988