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79-676: In AmigaOS 1.x, AmigaDOS is based on a TRIPOS port by MetaComCo , written in BCPL . BCPL does not use native pointers , so the more advanced functionality of the operating system was difficult to use and error-prone. The third-party AmigaDOS Resource Project (ARP, formerly the AmigaDOS Replacement Project ), a project begun by Amiga developer Charlie Heath, replaced many of the BCPL utilities with smaller, more sophisticated equivalents written in C and assembler , and provided

158-468: A recursive descent parser via sub-rules. The use of regexes in structured information standards for document and database modeling started in the 1960s and expanded in the 1980s when industry standards like ISO SGML (precursored by ANSI "GCA 101-1983") consolidated. The kernel of the structure specification language standards consists of regexes. Its use is evident in the DTD element group syntax. Prior to

237-533: A wrapper library , arp.library . This eliminated the interfacing problems in applications by automatically performing conversions from native pointers (such as those used by C or assembler) to BCPL equivalents and vice versa for all AmigaDOS functions. From AmigaOS 2.x onwards, AmigaDOS was rewritten in C, retaining 1.x compatibility where possible. Starting with AmigaOS 4, AmigaDOS abandoned its legacy with BCPL. Starting from AmigaOS 4.1, AmigaDOS has been extended with 64-bit file-access support. The Amiga console

316-591: A "lazy match" (see below) extension. As a result, very few programs actually implement the POSIX subexpression rules (even when they implement other parts of the POSIX syntax). The meaning of metacharacters escaped with a backslash is reversed for some characters in the POSIX Extended Regular Expression ( ERE ) syntax. With this syntax, a backslash causes the metacharacter to be treated as a literal character. So, for example, \( \)

395-803: A "standard" which has since been adopted as the default syntax of many tools, where the choice of BRE or ERE modes is usually a supported option. For example, GNU grep has the following options: " grep -E " for ERE, and " grep -G " for BRE (the default), and " grep -P " for Perl regexes. Perl regexes have become a de facto standard, having a rich and powerful set of atomic expressions. Perl has no "basic" or "extended" levels. As in POSIX EREs, ( ) and { } are treated as metacharacters unless escaped; other metacharacters are known to be literal or symbolic based on context alone. Additional functionality includes lazy matching , backreferences , named capture groups, and recursive patterns. In

474-477: A DOS3 disk cannot be read on a KS1.3 Amiga. However, any disk formatted with DOS0 using FFS or FFS2 can be read by any version of the Amiga operating system. For this reason, DOS0 tended to be the format of choice of software developers distributing on floppy, except where a custom filesystem and bootblock was used - a common practice in Amiga games. Where software needed AmigaOS 2 anyway, DOS3 was generally used. With

553-481: A bracket expression if it is the first (after the ^ , if present) character: []abc] , [^]abc] . Examples: According to Russ Cox, the POSIX specification requires ambiguous subexpressions to be handled in a way different from Perl's. The committee replaced Perl's rules with one that is simple to explain, but the new "simple" rules are actually more complex to implement: they were incompatible with pre-existing tooling and made it essentially impossible to define

632-493: A concise and flexible way to direct the automation of text processing of a variety of input data, in a form easy to type using a standard ASCII keyboard . A very simple case of a regular expression in this syntax is to locate a word spelled two different ways in a text editor , the regular expression seriali[sz]e matches both "serialise" and "serialize". Wildcard characters also achieve this, but are more limited in what they can pattern, as they have fewer metacharacters and

711-555: A finite alphabet Σ, the following constants are defined as regular expressions: Given regular expressions R and S, the following operations over them are defined to produce regular expressions: To avoid parentheses, it is assumed that the Kleene star has the highest priority followed by concatenation, then alternation. If there is no ambiguity, then parentheses may be omitted. For example, (ab)c can be written as abc , and a|(b(c*)) can be written as a|bc* . Many textbooks use

790-426: A given pattern or process a number of instances of it. Pattern matches may vary from a precise equality to a very general similarity, as controlled by the metacharacters. For example, . is a very general pattern, [a-z] (match all lower case letters from 'a' to 'z') is less general and b is a precise pattern (matches just 'b'). The metacharacter syntax is designed specifically to represent prescribed targets in

869-542: A large number of possible strings, rather than compiling a large list of all the literal possibilities. Depending on the regex processor there are about fourteen metacharacters, characters that may or may not have their literal character meaning, depending on context, or whether they are "escaped", i.e. preceded by an escape sequence , in this case, the backslash \ . Modern and POSIX extended regexes use metacharacters more often than their literal meaning, so to avoid "backslash-osis" or leaning toothpick syndrome , they have

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948-509: A larger set of characters. For example, [A-Z] could stand for any uppercase letter in the English alphabet, and \ d could mean any digit. Character classes apply to both POSIX levels. When specifying a range of characters, such as [a-Z] (i.e. lowercase a to uppercase Z ), the computer's locale settings determine the contents by the numeric ordering of the character encoding. They could store digits in that sequence, or

1027-421: A metacharacter escape to a literal mode; starting out, however, they instead have the four bracketing metacharacters ( ) and { } be primarily literal, and "escape" this usual meaning to become metacharacters. Common standards implement both. The usual metacharacters are {}[]()^$ .|*+? and \ . The usual characters that become metacharacters when escaped are dswDSW and N . When entering

1106-418: A new filesystem called JXFS capable to support partitions over a terabyte of size. Alternate filesystems from third-party manufacturers include Professional FileSystem , which is a filesystem with an easy structure, based on metadata , allowing high internal coherence, capable of defragmenting itself on the fly, and does not require to be unmounted before being mounted again; and Smart FileSystem which

1185-487: A new version of FFS called FastFileSystem 2. FFS2 incorporated all of the features of the original FFS including, as its author put it, "some minor changes". In order to preserve backwards compatibility, there were no major structural changes. (However, FF2 on AmigaOS 4.1 differs in that it can expand its features and capabilities with the aid of plug-ins ). As with FFS2, the AmigaOS 4 and MorphOS version of Smart FileSystem

1264-452: A range of lines (matching the pattern), which can be combined with other commands on either side, most famously g/re/p as in grep ("global regex print"), which is included in most Unix -based operating systems, such as Linux distributions. A similar convention is used in sed , where search and replace is given by s/re/replacement/ and patterns can be joined with a comma to specify a range of lines as in /re1/,/re2/ . This notation

1343-429: A regex in a programming language, they may be represented as a usual string literal, hence usually quoted; this is common in C, Java, and Python for instance, where the regex re is entered as "re" . However, they are often written with slashes as delimiters , as in /re/ for the regex re . This originates in ed , where / is the editor command for searching, and an expression /re/ can be used to specify

1422-497: A regular expression (that is, each character in the string describing its pattern) is either a metacharacter , having a special meaning, or a regular character that has a literal meaning. For example, in the regex b. , 'b' is a literal character that matches just 'b', while '.' is a metacharacter that matches every character except a newline. Therefore, this regex matches, for example, 'b%', or 'bx', or 'b5'. Together, metacharacters and literal characters can be used to identify text of

1501-503: A regular expression in the above syntax into an internal representation that can be executed and matched against a string representing the text being searched in. One possible approach is the Thompson's construction algorithm to construct a nondeterministic finite automaton (NFA), which is then made deterministic and the resulting deterministic finite automaton (DFA) is run on the target text string to recognize substrings that match

1580-408: A regular expression. For instance, determining the validity of a given ISBN requires computing the modulus of the integer base 11, and can be easily implemented with an 11-state DFA. However, converting it to a regular expression results in a 2,14 megabytes file . Given a regular expression, Thompson's construction algorithm computes an equivalent nondeterministic finite automaton. A conversion in

1659-412: A script program, AmigaDOS uses the command Execute . This executes the script called "myscript". This method of executing scripts keeps the console window busy until the script has finished its scheduled job. Users cannot interact with the console window until the script ends or until they interrupt it. While: The AmigaDOS command Run executes any DOS command or any kind of program and keeps

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1738-431: A significant difference in compactness. Some classes of regular languages can only be described by deterministic finite automata whose size grows exponentially in the size of the shortest equivalent regular expressions. The standard example here is the languages L k consisting of all strings over the alphabet { a , b } whose k th-from-last letter equals  a . On the one hand, a regular expression describing L 4

1817-503: A simple language-base. The usual context of wildcard characters is in globbing similar names in a list of files, whereas regexes are usually employed in applications that pattern-match text strings in general. For example, the regex ^ [ \t] +| [ \t] +$ matches excess whitespace at the beginning or end of a line. An advanced regular expression that matches any numeral is [+-] ?( \ d +( \ . \ d *)?| \ . \ d +)( [eE][+-] ? \ d +)? . A regex processor translates

1896-474: A union of their contents. For example, FONTS: might be assigned to SYS:Fonts , then extended to include, for example, Work:UserFonts using the add option of the AmigaDos assign command. The system would then permit use of fonts installed in either directory. Listing FONTS: would show the files from both locations. The physical device DF0: shares the same floppy drive mechanics with PC0: , which

1975-579: A virtual volume name to their installation directory (for instance, a fictional word processor called Writer might assign Writer: to DH0:Productivity/Writer ). This allows for easy relocation of installed programs. The default name SYS: is used to refer to the volume that the system was booted from. Various other default names are provided to refer to important system locations. e.g. S: for startup scripts, C: for AmigaDOS commands, FONTS: for installed fonts, etc. Assignment of volume labels can also be set on multiple directories, which will be treated as

2054-714: A wide range of programs, with these early forms standardized in the POSIX.2 standard in 1992. In the 1980s, the more complicated regexes arose in Perl , which originally derived from a regex library written by Henry Spencer (1986), who later wrote an implementation for Tcl called Advanced Regular Expressions . The Tcl library is a hybrid NFA / DFA implementation with improved performance characteristics. Software projects that have adopted Spencer's Tcl regular expression implementation include PostgreSQL . Perl later expanded on Spencer's original library to add many new features. Part of

2133-646: Is deprecated , in favor of BRE, as both provide backward compatibility . The subsection below covering the character classes applies to both BRE and ERE. BRE and ERE work together. ERE adds ? , + , and | , and it removes the need to escape the metacharacters ( ) and { } , which are required in BRE. Furthermore, as long as the POSIX standard syntax for regexes is adhered to, there can be, and often is, additional syntax to serve specific (yet POSIX compliant) applications. Although POSIX.2 leaves some implementation specifics undefined, BRE and ERE provide

2212-431: Is a greedy quantifier or not); a logical OR character, which offers a set of alternatives, and a logical NOT character, which negates an atom's existence; and backreferences to refer to previous atoms of a completing pattern of atoms. A match is made, not when all the atoms of the string are matched, but rather when all the pattern atoms in the regex have matched. The idea is to make a small pattern of characters stand for

2291-663: Is a journaling filesystem which performs journaled activities during system inactivities, and has been chosen by MorphOS as its standard filesystem. Old File System / Fast File System Fast File System 2 (AmigaOS4.x/MorphOS) Both DOS6 and DOS7 feature International filenames featured in DOS2 and DO3, but not Directory Caching, which was abandoned due to bugs in the original implementation. DOS4 and DOS5 are not recommended for use for this reason. Dostypes are backwards compatible with each other, but not forward compatible . A DOS7 formatted disk cannot be read on original Amiga FFS, and

2370-476: Is a fork of original SFS and are not 100% compatible with it. Other filesystems like FAT12 , FAT16 , FAT32 from Windows or ext2 from Linux are available through easily installable ( drag and drop ) system libraries or third party modules such as FAT95 (features read/write support), which can be found on the Aminet software repository. MorphOS 2 has built-in support for FAT filesystems. AmigaOS 4.1 adopted

2449-508: Is a sequence of characters that specifies a match pattern in text . Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings , or for input validation . Regular expression techniques are developed in theoretical computer science and formal language theory. The concept of regular expressions began in the 1950s, when the American mathematician Stephen Cole Kleene formalized

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2528-489: Is a simple mapping from regular expressions to the more general nondeterministic finite automata (NFAs) that does not lead to such a blowup in size; for this reason NFAs are often used as alternative representations of regular languages. NFAs are a simple variation of the type-3 grammars of the Chomsky hierarchy . In the opposite direction, there are many languages easily described by a DFA that are not easily described by

2607-535: Is a standard Amiga virtual device , normally assigned to CON: and driven by console.handler . It was developed from a primitive interface in AmigaOS 1.1, and became stable with versions 1.2 and 1.3, when it started to be known as AmigaShell and its original handler was replaced by newconsole.handler ( NEWCON: ). The console has various features that were considered up to date when it was created in 1985, like command template help, redirection to null (" NIL: "), and ANSI color terminal. The new console handler – which

2686-511: Is also used to store other system settings than just string variables (such as system settings, default icons and more), it tends to grow large over time, and copying everything over to ENV: located on RAM disk becomes expensive. This has led to alternative ways to set up ENV: by using dedicated ramdisk handlers that only copy files over from ENVARC: when the files are requested. Examples of such handlers are and. An example demonstrating creative abuse of global variables as well as Lab and Skip

2765-630: Is as follows. The "?" wildcard indicates "any character". Prefixing this with a "#" indicates "any number of repetitions". This can be viewed as analogous to the regular expression ".*". AmigaDOS also has the feature of dealing with batch programming, which it calls "script" programming, and has a number of commands such as Echo , If , Then , EndIf , Val , and Skip to deal with structured script programming. Scripts are text-based files and can be created with AmigaDOS's internal text editor program, called Ed (unrelated to Unix's Ed ), or with any other third-party text editor. To invoke

2844-556: Is by default an assign to RAM:Env, and ENVARC: is an assign to SYS:Prefs/Env-archive where SYS: refers to the boot device . On bootup, the content of ENVARC: is copied to ENV: for accessibility. When programming AmigaDOS scripts, one must keep in mind that global variables are system-wide. All script-internal variables shall be set using local variables, or one risks conflicts over global variables between scripts. Also, global variables require filesystem access, which typically makes them slower to access than local variables. Since ENVARC:

2923-409: Is expected, in contrast to for example on Linux , where "mv foo Foo" results in the error message "mv: `foo' and `Foo' are the same file" on case-insensitive filesystems like VFAT . Partitions and physical drives are typically referred to as DF0: (floppy drive 0), DH0: (hard drive 0), etc. However, unlike many operating systems, outside of built-in physical hardware devices like DF0: or HD0: ,

3002-464: Is given by ( a ∣ b ) ∗ a ( a ∣ b ) ( a ∣ b ) ( a ∣ b ) {\displaystyle (a\mid b)^{*}a(a\mid b)(a\mid b)(a\mid b)} . Generalizing this pattern to L k gives the expression: On the other hand, it is known that every deterministic finite automaton accepting the language L k must have at least 2 states. Luckily, there

3081-413: Is given in § Syntax . Regular expressions describe regular languages in formal language theory . They have the same expressive power as regular grammars . Regular expressions consist of constants, which denote sets of strings, and operator symbols, which denote operations over these sets. The following definition is standard, and found as such in most textbooks on formal language theory. Given

3160-430: Is now ( ) and \{ \} is now { } . Additionally, support is removed for \ n backreferences and the following metacharacters are added: Examples: POSIX Extended Regular Expressions can often be used with modern Unix utilities by including the command line flag -E . The character class is the most basic regex concept after a literal match. It makes one small sequence of characters match

3239-601: Is particularly well known due to its use in Perl , where it forms part of the syntax distinct from normal string literals. In some cases, such as sed and Perl, alternative delimiters can be used to avoid collision with contents, and to avoid having to escape occurrences of the delimiter character in the contents. For example, in sed the command s,/,X, will replace a / with an X , using commas as delimiters. The IEEE POSIX standard has three sets of compliance: BRE (Basic Regular Expressions), ERE (Extended Regular Expressions), and SRE (Simple Regular Expressions). SRE

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3318-502: Is the AmigaDOS variant of the infamous GOTO . AmigaDOS is in general case-insensitive . Indicating a device as "Dh0:", "DH0:" or "dh0:" always refers to the same partition ; however, for file and directory names, this is filesystem-dependent, and some filesystems allow case sensitivity as a flag upon formatting. An example of such a file system is Smart File System . This is very convenient when dealing with software ported over from

3397-549: Is the CrossDOS virtual device capable of reading PC formatted floppy disks. When any PC formatted floppy disk is inserted into the floppy drive, then the DF0: floppy Amiga icon will change to indicate that the disk is unknown to the normal Amiga device, and it will show four question marks ???? as the standard "unknown" volume name, while the PC0: icon will appear revealing the name of

3476-418: Is to list its elements or members. However, there are often more concise ways: for example, the set containing the three strings "Handel", "Händel", and "Haendel" can be specified by the pattern H(ä|ae?)ndel ; we say that this pattern matches each of the three strings. However, there can be many ways to write a regular expression for the same set of strings: for example, (Hän|Han|Haen)del also specifies

3555-419: Is used by many modern tools including PHP and Apache HTTP Server . Today, regexes are widely supported in programming languages, text processing programs (particularly lexers ), advanced text editors, and some other programs. Regex support is part of the standard library of many programming languages, including Java and Python , and is built into the syntax of others, including Perl and ECMAScript . In

3634-439: The ← Backspace key (to delete all of the input) or by pressing ↵ Enter (which will cause the input to be processed as a command as soon as the current command stops running). Like other operating systems, AmigaDOS also provides wildcard characters that are substitutes for any character or any sequence of random characters in a string. Here is an example of wildcard characters in AmigaDOS commands: The parsing of this

3713-549: The Compatible Time-Sharing System , an important early example of JIT compilation. He later added this capability to the Unix editor ed , which eventually led to the popular search tool grep 's use of regular expressions ("grep" is a word derived from the command for regular expression searching in the ed editor: g/ re /p meaning "Global search for Regular Expression and Print matching lines"). Around

3792-545: The Kleene star and set unions over finite words. This is a surprisingly difficult problem. As simple as the regular expressions are, there is no method to systematically rewrite them to some normal form. The lack of axiom in the past led to the star height problem . In 1991, Dexter Kozen axiomatized regular expressions as a Kleene algebra , using equational and Horn clause axioms. Already in 1964, Redko had proved that no finite set of purely equational axioms can characterize

3871-461: The POSIX standard, Basic Regular Syntax ( BRE ) requires that the metacharacters ( ) and { } be designated \(\) and \{\} , whereas Extended Regular Syntax ( ERE ) does not. The - character is treated as a literal character if it is the last or the first (after the ^ , if present) character within the brackets: [abc-] , [-abc] , [^-abc] . Backslash escapes are not allowed. The ] character can be included in

3950-604: The SNOBOL language, which did not use regular expressions, but instead its own pattern matching constructs. Regular expressions entered popular use from 1968 in two uses: pattern matching in a text editor and lexical analysis in a compiler. Among the first appearances of regular expressions in program form was when Ken Thompson built Kleene's notation into the editor QED as a means to match patterns in text files . For speed, Thompson implemented regular expression matching by just-in-time compilation (JIT) to IBM 7094 code on

4029-470: The July 2007 Update of AmigaOS 4.0 in 2007, the first two plug-ins for FFS2 were released: AmigaDOS has only a single mandated filename extension: ".info", which must be appended to the filename of each icon. If a file called myprog exists, then its icon file must be called myprog.info . In addition to image data, the icon file also records program metadata such as options and keywords, its own position on

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4108-476: The PC formatted disk. Any disk change with Amiga formatted disks will invert this behaviour. AmigaDOS supports various filesystems and variants. The first filesystem was simply called Amiga FileSystem , and was suitable mainly for floppy disks, because it did not support automatic booting from hard disks (on floppy, booting was done using code from the bootblock). It was soon replaced by FastFileSystem (FFS), and hence

4187-450: The algebra of regular languages. A regex pattern matches a target string . The pattern is composed of a sequence of atoms . An atom is a single point within the regex pattern which it tries to match to the target string. The simplest atom is a literal, but grouping parts of the pattern to match an atom will require using ( ) as metacharacters. Metacharacters help form: atoms ; quantifiers telling how many atoms (and whether it

4266-416: The complement operator is redundant, because it does not grant any more expressive power. However, it can make a regular expression much more concise—eliminating a single complement operator can cause a double exponential blow-up of its length. Regular expressions in this sense can express the regular languages, exactly the class of languages accepted by deterministic finite automata . There is, however,

4345-862: The concept of a regular language . They came into common use with Unix text-processing utilities. Different syntaxes for writing regular expressions have existed since the 1980s, one being the POSIX standard and another, widely used, being the Perl syntax. Regular expressions are used in search engines , in search and replace dialogs of word processors and text editors , in text processing utilities such as sed and AWK , and in lexical analysis . Regular expressions are supported in many programming languages. Library implementations are often called an " engine ", and many of these are available for reuse. Regular expressions originated in 1951, when mathematician Stephen Cole Kleene described regular languages using his mathematical notation called regular events . These arose in theoretical computer science , in

4424-651: The console free for further input. Protection bits are flags that files, links and directories have in the filesystem. To change them one can either use the command Protect , or use the Information entry from the Icons menu in Workbench on selected files. AmigaDOS supports the following set of protection bits (abbreviated as HSPARWED): The H-bit has often been misunderstood to mean "Hide". In Smart File System (SFS) files and directories with H-bit set are hidden from

4503-604: The current shell. In case of name collision, local variables have precedence over global variables. Global variables can be set using the command SetEnv , while local variables can be set using the command Set . There are also the commands GetEnv and Get that can be used to print out global and local variables. The examples below demonstrate simple usage: Global variables are kept as files in ENV: , and optionally saved on disk in ENVARC: to survive reboot and power cycling . ENV:

4582-424: The desktop (AmigaOS can "snapshot" icons in places defined by the user), and other information about the file. Directory window size and position information is stored in the ".info" file associated with the directory, and disk icon information is stored in "Disk.info" in the root of the volume. With the exception of icons, the Amiga system does not identify file types using extensions, but instead will examine either

4661-452: The effort in the design of Raku (formerly named Perl 6) is to improve Perl's regex integration, and to increase their scope and capabilities to allow the definition of parsing expression grammars . The result is a mini-language called Raku rules , which are used to define Raku grammar as well as provide a tool to programmers in the language. These rules maintain existing features of Perl 5.x regexes, but also allow BNF -style definition of

4740-632: The icon associated with a file or the binary header of the file itself to determine the file type. TRIPOS Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.236 via cp1112 cp1112, Varnish XID 933984374 Upstream caches: cp1112 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 08:40:04 GMT Regular expression A regular expression (shortened as regex or regexp ), sometimes referred to as rational expression ,

4819-552: The keyboard. This is an example of typical AmigaDOS command syntax: AmigaDOS can redirect the output of a command to files, pipes, a printer, the null device, and other Amiga devices. AmigaDOS commands are expected to provide a standard "template" that describes the arguments they can accept. This can be used as a basic "help" feature for commands, although third-party replacement console handlers and shells , such as Bash or Zshell (ported from Unix ), or KingCON often provide more verbose help for built-in commands. On requesting

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4898-413: The late 2010s, several companies started to offer hardware, FPGA , GPU implementations of PCRE compatible regex engines that are faster compared to CPU implementations . The phrase regular expressions , or regexes , is often used to mean the specific, standard textual syntax for representing patterns for matching text, as distinct from the mathematical notation described below. Each character in

4977-576: The mid-1980s, AmigaDOS does not implement a proprietary character set; the developers chose to use the ANSI– ISO standard ISO-8859-1 (Latin 1) , which includes the ASCII character set. As in Unix systems, the Amiga console accepts only linefeed (" LF ") as an end-of-line (" EOL ") character. The Amiga console has support for accented characters as well as for characters created by combinations of 'dead keys' on

5056-425: The mostly case-sensitive Un*x world, but causes much confusion for native Amiga applications, which assume case insensitivity. Advanced users will hence typically only use the case sensitivity flag for file systems used for software originating from Un*x. Re-casing of file, directory and volume names is allowed using ordinary methods; the commands "rename foo Foo" and "relabel Bar: bAr:" are valid and do exactly what

5135-402: The names of the single disks, volumes and partitions are totally arbitrary: for example a hard disk partition could be named Work or System , or anything else at the time of its creation. Volume names can be used in place of the corresponding device names, so a disk partition on device DH0: called Workbench could be accessed either with the name DH0: or Workbench: . Users must indicate to

5214-403: The opposite direction is achieved by Kleene's algorithm . Finally, many real-world "regular expression" engines implement features that cannot be described by the regular expressions in the sense of formal language theory; rather, they implement regexes . See below for more on this. As seen in many of the examples above, there is more than one way to construct a regular expression to achieve

5293-534: The original filesystem was known by the name of "Old" FileSystem (OFS). FFS was more efficient on space and quite measurably faster than OFS, hence the name. With AmigaOS 2.x, FFS became an official part of the OS and was soon expanded to recognise cached partitions, international partitions allowing accented characters in file and partition names, and finally (with MorphOS and AmigaOS 4 ) long filenames, up to 108 characters (from 31). Both AmigaOS 4.x and MorphOS featured

5372-453: The regular expression. The picture shows the NFA scheme N ( s *) obtained from the regular expression s * , where s denotes a simpler regular expression in turn, which has already been recursively translated to the NFA N ( s ). A regular expression, often called a pattern , specifies a set of strings required for a particular purpose. A simple way to specify a finite set of strings

5451-490: The same regular language, for all regular expressions X , Y , it is necessary and sufficient to check whether the particular regular expressions ( a + b ) and ( a b ) denote the same language over the alphabet Σ={ a , b }. More generally, an equation E = F between regular-expression terms with variables holds if, and only if, its instantiation with different variables replaced by different symbol constants holds. Every regular expression can be written solely in terms of

5530-484: The same results. It is possible to write an algorithm that, for two given regular expressions, decides whether the described languages are equal; the algorithm reduces each expression to a minimal deterministic finite state machine , and determines whether they are isomorphic (equivalent). Algebraic laws for regular expressions can be obtained using a method by Gischer which is best explained along an example: In order to check whether ( X + Y ) and ( X Y ) denote

5609-407: The same set of three strings in this example. Most formalisms provide the following operations to construct regular expressions. These constructions can be combined to form arbitrarily complex expressions, much like one can construct arithmetical expressions from numbers and the operations +, −, ×, and ÷. The precise syntax for regular expressions varies among tools and with context; more detail

5688-505: The same time when Thompson developed QED, a group of researchers including Douglas T. Ross implemented a tool based on regular expressions that is used for lexical analysis in compiler design. Many variations of these original forms of regular expressions were used in Unix programs at Bell Labs in the 1970s, including lex , sed , AWK , and expr , and in other programs such as vi , and Emacs (which has its own, incompatible syntax and behavior). Regexes were subsequently adopted by

5767-421: The subfields of automata theory (models of computation) and the description and classification of formal languages , motivated by Kleene's attempt to describe early artificial neural networks . (Kleene introduced it as an alternative to McCulloch & Pitts's "prehensible", but admitted "We would welcome any suggestions as to a more descriptive term." ) Other early implementations of pattern matching include

5846-425: The symbols ∪, +, or ∨ for alternation instead of the vertical bar. Examples: The formal definition of regular expressions is minimal on purpose, and avoids defining ? and + —these can be expressed as follows: a+ = aa* , and a? = (a|ε) . Sometimes the complement operator is added, to give a generalized regular expression ; here R matches all strings over Σ* that do not match R . In principle,

5925-469: The system that " Workbench " is the volume " Workbench: " by always typing the colon " : " when they are entering information in a requester form or into AmigaShell. If an accessed volume name cannot be found, the operating system will prompt the user to insert the disk with the given volume name, or allow the user to cancel the operation. In addition, logical device names can be set with the "assign" command to any directory or device; programs often assigned

6004-448: The system. It is still possible access hidden files but they don't appear in any directory listings. Demonstration of H-bit in action: As any other DOS, Amiga deals with environment variables as used in batch programming. There are both global and local variables, and they are referred to with a dollar sign in front of the variable name, for example $ myvar . Global variables are available system-wide; local variables are only valid in

6083-401: The template for the command " Copy ", the following output is obtained: By reading this template, a user can know that the following syntax is acceptable for the command: A user can terminate a program by invoking the key combination Ctrl + C or Ctrl + D . Pressing space or any printing character on the keyboard suspends the console output. Output may be resumed by pressing

6162-484: The use of regular expressions, many search languages allowed simple wildcards, for example "*" to match any sequence of characters, and "?" to match a single character. Relics of this can be found today in the glob syntax for filenames, and in the SQL LIKE operator. Starting in 1997, Philip Hazel developed PCRE (Perl Compatible Regular Expressions), which attempts to closely mimic Perl's regex functionality and

6241-407: Was implemented in release 1.2 – allows many more features, such as command history , pipelines , and automatic creation of files when output is redirected . When TCP/IP stacks like AmiTCP were released in the early 1990s, the console could also receive redirection from Internet-enabled Amiga device handlers (e.g., TCP: , copy file TO TCP:Site/Port ). Unlike other systems originally launched in

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