Regex¶
Usage
use Regex;
or
import Regex;
Regular expression support.
The regular expression support is built on top of the RE2 regular expression library. As such, the exact regular expression syntax available is the syntax from RE2, which is available within the RE2 project at https://github.com/google/re2 and included here for your convenience.
Enabling Regular Expression Support¶
Setting the environment variable CHPL_RE2 to bundled will enable regular expression support with the RE2 library:
export CHPL_RE2=bundled
Then, rebuild Chapel. The RE2 library will be expanded from a release included in the Chapel distribution.
Note
if re2 support is not enabled (which is the case in quickstart configurations as in Chapel Quickstart Instructions), the functionality described below will result in either a compile-time or a run-time error.
Using Regular Expression Support¶
Chapel supports both string and bytes regular expressions.
use Regex;
var myRegex = new regex("a+"); // b"a+" for matching arbitrary bytes values
Now you can use these methods on regular expressions: regex.search
,
regex.match
, regex.split
, regex.matches
.
Lastly, you can include regular expressions in the format string for
readf
for searching on QIO channels using the %/<regex>/
syntax.
Regular Expression Examples¶
a+
Match one or more
a
characters[[:space:]]*
or\s*
(which would be"\\s*"
in a string)Match zero or more spaces
[[:digit:]]+
or\d+
(which would be"\\d+"
in a string)Match one or more digits
([a-zA-Z0-9]+[[:space:]]+=[[:space:]]+[0-9]+
Match sequences of the form <letters-and-digits> <spaces>
=
<digits>
RE2 regular expression syntax reference¶
Single characters:
. any character, possibly including newline (s=true)
[xyz] character class
[^xyz] negated character class
\d Perl character class (see below)
\D negated Perl character class (see below)
[:alpha:] ASCII character class
[:^alpha:] negated ASCII character class
\pN Unicode character class (one-letter name)
\p{Greek} Unicode character class
\PN negated Unicode character class (one-letter name)
\P{Greek} negated Unicode character class
Composites:
xy «x» followed by «y»
x|y «x» or «y» (prefer «x»)
Repetitions:
x* zero or more «x», prefer more
x+ one or more «x», prefer more
x? zero or one «x», prefer one
x{n,m} «n» or «n»+1 or ... or «m» «x», prefer more
x{n,} «n» or more «x», prefer more
x{n} exactly «n» «x»
x*? zero or more «x», prefer fewer
x+? one or more «x», prefer fewer
x?? zero or one «x», prefer zero
x{n,m}? «n» or «n»+1 or ... or «m» «x», prefer fewer
x{n,}? «n» or more «x», prefer fewer
x{n}? exactly «n» «x»
Grouping:
(re) numbered capturing group
(?P<name>re) named & numbered capturing group
(?:re) non-capturing group
(?flags) set flags within current group; non-capturing
(?flags:re) set flags during re; non-capturing
Flags:
i case-insensitive (default false)
m multi-line mode: «^» and «$» match begin/end line in addition to
begin/end text (default false)
s let «.» match «\n» (default false)
U ungreedy: swap meaning of «x*» and «x*?», «x+» and «x+?», etc.
(default false)
Flag syntax is:
«xyz» (set)
«-xyz» (clear)
«xy-z» (set «xy», clear «z»)
Empty strings:
^ at beginning of text or line («m»=true)
$ at end of text (like «\z» not «\Z») or line («m»=true)
\A at beginning of text
\b at word boundary («\w» on one side and «\W», «\A», or «\z» on the
other)
\B not a word boundary
\z at end of text
Escape sequences:
\a bell (== \007)
\f form feed (== \014)
\t horizontal tab (== \011)
\n newline (== \012)
\r carriage return (== \015)
\v vertical tab character (== \013)
\* literal «*», for any punctuation character «*»
\123 octal character code (up to three digits)
\x7F hex character code (exactly two digits)
\x{10FFFF} hex character code
\C match a single byte even in UTF-8 mode
\Q...\E literal text «...» even if «...» has punctuation
Character class elements:
x single character
A-Z character range (inclusive)
\d Perl character class (see below)
[:foo:] ASCII character class «foo»
\p{Foo} Unicode character class «Foo»
\pF Unicode character class «F» (one-letter name)
Named character classes as character class elements:
[\d] digits (== \d)
[^\d] not digits (== \D)
[\D] not digits (== \D)
[^\D] not not digits (== \d)
[[:name:]] named ASCII class inside character class (== [:name:])
[^[:name:]] named ASCII class inside negated character class (== [:^name:])
[\p{Name}] named Unicode property inside character class (== \p{Name})
[^\p{Name}] named Unicode property inside negated character class (==\P{Name})
Perl character classes:
\d digits (== [0-9])
\D not digits (== [^0-9])
\s whitespace (== [\t\n\f\r ])
\S not whitespace (== [^\t\n\f\r ])
\w word characters (== [0-9A-Za-z_])
\W not word characters (== [^0-9A-Za-z_])
ASCII character classes::
Note -- you must use these within a [] group! so if you want
to match any number of spaces, use [[:space:]]* or \s*
[:alnum:] alphanumeric (== [0-9A-Za-z])
[:alpha:] alphabetic (== [A-Za-z])
[:ascii:] ASCII (== [\x00-\x7F])
[:blank:] blank (== [\t ])
[:cntrl:] control (== [\x00-\x1F\x7F])
[:digit:] digits (== [0-9])
[:graph:] graphical (== [!-~] ==
[A-Za-z0-9!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~])
[:lower:] lower case (== [a-z])
[:print:] printable (== [ -~] == [[:graph:]])
[:punct:] punctuation (== [!-/:-@[-`{-~])
[:space:] whitespace (== [\t\n\v\f\r ])
[:upper:] upper case (== [A-Z])
[:word:] word characters (== [0-9A-Za-z_])
[:xdigit:] hex digit (== [0-9A-Fa-f])
Unicode character class names--general category:
C other
Cc control
Cf format
Co private use
Cs surrogate
L letter
Ll lowercase letter
Lm modifier letter
Lo other letter
Lt titlecase letter
Lu uppercase letter
M mark
Mc spacing mark
Me enclosing mark
Mn non-spacing mark
N number
Nd decimal number
Nl letter number
No other number
P punctuation
Pc connector punctuation
Pd dash punctuation
Pe close punctuation
Pf final punctuation
Pi initial punctuation
Po other punctuation
Ps open punctuation
S symbol
Sc currency symbol
Sk modifier symbol
Sm math symbol
So other symbol
Z separator
Zl line separator
Zp paragraph separator
Zs space separator
Unicode character class names--scripts (with explanation where non-trivial):
Arabic
Armenian
Balinese
Bengali
Bopomofo
Braille
Buginese
Buhid
Canadian_Aboriginal
Carian
Cham
Cherokee
Common characters not specific to one script
Coptic
Cuneiform
Cypriot
Cyrillic
Deseret
Devanagari
Ethiopic
Georgian
Glagolitic
Gothic
Greek
Gujarati
Gurmukhi
Han
Hangul
Hanunoo
Hebrew
Hiragana
Inherited inherit script from previous character
Kannada
Katakana
Kayah_Li
Kharoshthi
Khmer
Lao
Latin
Lepcha
Limbu
Linear_B
Lycian
Lydian
Malayalam
Mongolian
Myanmar
New_Tai_Lue aka Simplified Tai Lue
Nko
Ogham
Ol_Chiki
Old_Italic
Old_Persian
Oriya
Osmanya
Phags_Pa
Phoenician
Rejang
Runic
Saurashtra
Shavian
Sinhala
Sundanese
Syloti_Nagri
Syriac
Tagalog
Tagbanwa
Tai_Le
Tamil
Telugu
Thaana
Thai
Tibetan
Tifinagh
Ugaritic
Vai
Yi
Vim character classes:
\d digits (== [0-9])
\D not «\d»
\w word character
\W not «\w»
Regular Expression Types and Methods¶
- class BadRegexError : Error¶
Error thrown if a regular expression fails to compile
- record regexMatch¶
The regexMatch record records a regular expression search match or a capture group.
Regular expression search routines normally return one of these. Also, this type can be passed as a capture group argument. Lastly, something of type regexMatch can be checked for a match in a simple if statement, as in:
var m:regexMatch = ...; if m then do_something_if_matched(); if !m then do_something_if_not_matched();
- var matched : bool¶
true if the regular expression search matched successfully
- var byteOffset : byteIndex¶
0-based offset into the string or channel that matched; -1 if matched=false
- var numBytes : int¶
the length of the match. 0 if matched==false
- proc string.this(m: regexMatch)¶
This function extracts the part of a string matching a regular expression or capture group. This method is intended to be called on the same string used as the text in a regular expression search.
- Arguments:
m – a match (e.g. returned by
regex.search
)- Returns:
the portion of
this
referred to by the match
- proc bytes.this(m: regexMatch)¶
This function extracts the part of a bytes matching a regular expression or capture group. This method is intended to be called on the same bytes used as the text in a regular expression search.
- Arguments:
m – a match (e.g. returned by
regex.search
)- Returns:
the portion of
this
referred to by the match
- record regex : serializable¶
This record represents a compiled regular expression. Regular expressions are currently cached on a per-thread basis and are reference counted.
A string-based regex can be cast to a string (resulting in the pattern that was compiled). A string can be cast to a string-based regex (resulting in a compiled regex). Same applies for bytes.
- proc init(pattern: ?t, posix = false, literal = false, noCapture = false, ignoreCase = false, multiLine = posix, dotAll = false, nonGreedy = false) throws where t == string || t == bytes¶
Initializer for a compiled regular expression.
new regex()
throws aBadRegexError
if compilation failed.- Arguments:
pattern – the regular expression to compile. This argument can be string or bytes. See RE2 regular expression syntax reference for details. Note that you may have to escape backslashes. For example, to get the regular expression
\s
, you’d have to write"\\s"
because the\
is the escape character within Chapel string/bytes literals. Note that, Chapel supports triple-quoted raw string/bytes literals, which do not require escaping backslashes. For example"""\s"""
orb"""\s"""
can be used.posix – (optional) set to true to disable non-POSIX regular expression syntax and to prefer the left-most longest match, instead of the first match in the pattern. This mode is intended to match egrep regular expression syntax.
literal – (optional) set to true to treat the regular expression as a literal (ie, create a regex matching
pattern
as a string rather than as a regular expression). Ifliteral=true
, all other optional flags are ignored.noCapture – (optional) set to true in order to disable all capture groups in the regular expression
ignoreCase – (optional) set to true in order to ignore case when matching. Note that this can be set inside the regular expression with
(?i)
.multiLine – (optional) set to true in order to activate multiline mode (meaning that
^
and$
match the beginning and end of a line instead of just the beginning and end of the text). Note that this can be set inside a regular expression with(?m)
. The default isfalse
for non-posix
regular expressions; andtrue
forposix
regular expressions.dotAll – (optional) set to true in order to allow
.
to match a newline. Note that this can be set inside the regular expression with(?s)
.nonGreedy – (optional) set to true in order to prefer shorter matches for repetitions; for example, normally x* will match as many x characters as possible and x*? will match as few as possible. This flag swaps the two, so that x* will match as few as possible and x*? will match as many as possible. Note that this flag has no effect when
posix=true
. For non-posix regular expressions, it can alternatively be activated within a regular expression with(?U)
.
- Throws:
BadRegexError – If the argument ‘pattern’ has syntactical errors. Refer to https://github.com/google/re2/blob/master/re2/re2.h for more details about error codes.
- proc init(type exprType)
Default type initializer for a compiled regular expression. This does not initialize any fields and the resulting
regex
may produce erroneous results when used. The behavior may differ based on values ofCHPL_COMM
.Note
If you are looking to default initialize a
regex
, you might be looking fornew regex("")
, which will create a regular expression matching the empty string.
- proc search(text: exprType, ref captures ...?k) : regexMatch¶
Search within the passed text for the first match at any offset to this regular expression. This routine will try matching the regular expression at different offsets until a match is found. If you want to only match at the beginning of the pattern, you can start your pattern with
^
and end it with$
or useregex.match
. If a capture group was not matched, the corresponding argument will get the default value for its type.- Arguments:
text – a string or bytes to search
captures – (optional) what to capture from the regular expression. If the class:regex was based on string, then, these should be strings or types that strings can cast to. Same applies for bytes.
- Returns:
an
regexMatch
object representing the offset in text where a match occurred
- proc match(text: exprType, ref captures ...?k) : regexMatch¶
Check for a match to this regular expression at the start of the passed text. If a capture group was not matched, the corresponding argument will get the default value for its type.
For example, this function can be used to check to see if a string fits a particular template:
if myRegex.match("some string") { doSomethingIfMatched(); }
- Arguments:
text – a string or bytes to search
captures – what to capture from the regular expression. If the class:regex was based on string, then, these should be strings or types that strings can cast to. Same applies for bytes.
- Returns:
an
regexMatch
object representing the offset in text where a match occurred
- proc fullMatch(text: exprType, ref captures ...?k) : regexMatch¶
Check for a match to this regular expression in the full passed text. If a capture group was not matched, the corresponding argument will get the default value for its type.
- Arguments:
text – a string or bytes to search
captures – what to capture from the regular expression. If the class:regex was based on string, then, these should be strings or types that strings can cast to. Same applies for bytes.
- Returns:
an
regexMatch
object representing the offset in text where a match occurred
- iter split(text: exprType, maxsplit: int = 0)¶
Split the text by occurrences of this regular expression. If capturing parentheses are used in pattern, then the text of all groups in the pattern are also returned as part of the resulting array. If maxsplit is nonzero, at most maxsplit splits occur, and the remaining text is returned as the last element.
- Arguments:
text – a string or bytes to split
maxsplit – if nonzero, the maximum number of splits to do
- Yields:
each split portion, one at a time
- iter matches(text: exprType, param numCaptures = 0, maxMatches: int = max(int))¶
Yields matches and capture groups in the text, continuing until the end of the text or
maxMatches
is reached.- Arguments:
text – the string or bytes to search
numCaptures – (compile-time constant) the size of the captures to return
maxMatches – the maximum number of matches to return
- Yields:
tuples of
regexMatch
objects, the 1st is always the match for the whole pattern and the rest are the capture groups.
- proc string.find(pattern: regex(string)) : byteIndex¶
Search the receiving string for the result of a compiled regular expression. Search for matches at any offset.
- Arguments:
pattern – the compiled regular expression to search for
- Returns:
a byteIndex representing the offset in the receiving string where a match occurred
- proc bytes.find(pattern: regex(bytes)) : byteIndex¶
Search the receiving bytes for the result of a compiled regular expression. Search for matches at any offset.
- Arguments:
pattern – the compiled regular expression to search for
- Returns:
a byteIndex representing the offset in the receiving bytes where a match occurred
- proc string.replace(pattern: regex(string), replacement: string, count = -1) : string¶
Search the receiving string for the pattern. Returns a new string where the match(es) to the pattern is replaced with a replacement.
The replacement string can include the sequences
\1
to\9
to include text matching the corresponding parenthesized capture group from the pattern, and\0
to refer to the entire matching text.- Arguments:
pattern – the compiled regular expression to search for
replacement – string to replace with
count – number of maximum replacements to make, values less than zero replaces all occurrences
- proc bytes.replace(pattern: regex(bytes), replacement: bytes, count = -1) : bytes¶
Search the receiving bytes for the pattern. Returns a new bytes where the match(es) to the pattern is replaced with a replacement.
The replacement bytes can include the sequences
\1
to\9
to include text matching the corresponding parenthesized capture group from the pattern, and\0
to refer to the entire matching text.- Arguments:
pattern – the compiled regular expression to search for
replacement – bytes to replace with
count – number of maximum replacements to make, values less than zero replaces all occurrences
- proc string.replaceAndCount(pattern: regex(string), replacement: string, count = -1) : (string, int)¶
Search the receiving string for the pattern. Returns a new string where the match(es) to the pattern is replaced with a replacement and number of replacements.
The replacement string can include the sequences
\1
to\9
to include text matching the corresponding parenthesized capture group from the pattern, and\0
to refer to the entire matching text.- Arguments:
pattern – the compiled regular expression to search for
replacement – string to replace with
count – number of maximum replacements to make, values less than zero replaces all occurrences
- proc bytes.replaceAndCount(pattern: regex(bytes), replacement: bytes, count = -1) : (bytes, int)¶
Search the receiving bytes for the pattern. Returns a new bytes where the match(es) to the pattern is replaced with a replacement and number of replacements.
The replacement bytes can include the sequences
\1
to\9
to include text matching the corresponding parenthesized capture group from the pattern, and\0
to refer to the entire matching text.- Arguments:
pattern – the compiled regular expression to search for
replacement – bytes to replace with
count – number of maximum replacements to make, values less than zero replaces all occurrences
- proc string.startsWith(pattern: regex(string)) : bool¶
Returns true if the start of the string matches the pattern.
- Arguments:
pattern – the compiled regular expression to match
- Returns:
true if string starts with pattern, false otherwise
- proc bytes.startsWith(pattern: regex(bytes)) : bool¶
Returns true if the start of the bytes matches the pattern.
- Arguments:
pattern – the compiled regular expression to match
- Returns:
true if string starts with pattern, false otherwise
- iter string.split(sep: regex(string), maxsplit: int = 0)¶
Split the receiving string by occurrences of the passed regular expression by calling
regex.split
.- Arguments:
sep – the regular expression to use to split
maxsplit – if nonzero, the maximum number of splits to do
- Yields:
each split portion, one at a time
- iter bytes.split(sep: regex(bytes), maxsplit: int = 0)¶
Split the receiving bytes by occurrences of the passed regular expression by calling
regex.split
.- Arguments:
sep – the regular expression to use to split
maxsplit – if nonzero, the maximum number of splits to do
- Yields:
each split portion, one at a time
- proc fileReader.readThrough(separator: regex(?t), maxSize = -1, stripSeparator = false) : t throws where t == string || t == bytes¶
Read until a match with the given separator is found, returning the contents of the
fileReader
through that point.If a match is found, the
fileReader
position is left immediately after it. If the separator could not be found in the nextmaxSize
codepoints/bytes, aBadFormatError
is thrown and thefileReader
’s position is not changed. If EOF is reached before finding the separator, the remainder of thefileReader
’s contents are returned and the position is left at EOF.- Arguments:
separator – The
regex
separator to match with.maxSize – The maximum number of codepoints/bytes to read. For the default value of
-1
, this method can read until EOF.stripSeparator – Whether to strip the separator from the returned
string
orbytes
. Iftrue
, the returned value will not include the captured separator.
- Returns:
A
string
orbytes
with the contents of thefileReader
up to (and possibly including) the match.- Throws:
EofError – If nothing could be read because the
fileReader
was already at EOF.BadFormatError – If the separator was not found in the next
maxSize
bytes. ThefileReader
position is not moved.SystemError – If data could not be read from the
fileReader
.
- proc fileReader.readThrough(separator: regex(string), ref s: string, maxSize = -1, stripSeparator = false) : bool throws
Read until a match with the given separator is found, returning the contents of the
fileReader
through that point.See the above
overload
of this method for more details.- Arguments:
separator – The
regex
separator to match with.s – The
string
to read into. Contents will be overwritten.maxSize – The maximum number of codepoints to read. For the default value of
-1
, this method can read until EOF.stripSeparator – Whether to strip the separator from the returned
string
. Iftrue
, the captured separator will be removed froms
.
- Returns:
true
if something was read, andfalse
otherwise (i.e., thefileReader
was already at EOF).- Throws:
BadFormatError – If the separator was not found in the next
maxSize
bytes. ThefileReader
position is not moved.SystemError – If data could not be read from the
fileReader
.
- proc fileReader.readThrough(separator: regex(bytes), ref b: bytes, maxSize = -1, stripSeparator = false) : bool throws
Read until a match with the given separator is found, returning the contents of the
fileReader
through that point.See the above
overload
of this method for more details.- Arguments:
separator – The
regex
separator to match with.b – The
bytes
to read into. Contents will be overwritten.maxSize – The maximum number of bytes to read. For the default value of
-1
, this method can read until EOF.stripSeparator – Whether to strip the separator from the returned
bytes
. Iftrue
, the captured separator will be removed fromb
.
- Returns:
true
if something was read, andfalse
otherwise (i.e., thefileReader
was already at EOF).- Throws:
BadFormatError – If the separator was not found in the next
maxSize
bytes. ThefileReader
position is not moved.SystemError – If data could not be read from the
fileReader
.
- proc fileReader.readTo(separator: regex(?t), maxSize = -1) : t throws where t == string || t == bytes¶
Read until a match with the given separator is found, returning the contents of the
fileReader
up to that point.If a match is found, the
fileReader
position is left immediately before it. If the separator could not be found in the nextmaxSize
codepoints/bytes, aBadFormatError
is thrown and thefileReader
’s position is not changed. If EOF is reached before finding the separator, the remainder of thefileReader
’s contents are returned and the position is left at EOF.- Arguments:
separator – The
regex
separator to match with.maxSize – The maximum number of bytes to read. For the default value of
-1
, this method can read until EOF.
- Returns:
A
string
orbytes
with the contents of the channel up to theseparator
.- Throws:
EofError – If nothing could be read because the
fileReader
was already at EOF.BadFormatError – If the separator was not found in the next maxSize bytes. The
fileReader
position is not moved.SystemError – If data could not be read from the
fileReader
.
- proc fileReader.readTo(separator: regex(string), ref s: string, maxSize = -1) : bool throws
Read until a match with the given separator is found, returning the contents of the
fileReader
up to that point.See the above
overload
of this method for more details.- Arguments:
- Returns:
true
if something was read, andfalse
otherwise (i.e., thefileReader
was already at EOF).- Throws:
BadFormatError – If the separator was not found in the next maxSize codepoints. The
fileReader
position is not moved.SystemError – If data could not be read from the
fileReader
.
- proc fileReader.readTo(separator: regex(bytes), ref b: bytes, maxSize = -1) : bool throws
Read until a match with the given separator is found, returning the contents of the
fileReader
up to that point.See the above
overload
of this method for more details.- Arguments:
- Returns:
true
if something was read, andfalse
otherwise (i.e., thefileReader
was already at EOF).- Throws:
BadFormatError – If the separator was not found in the next maxSize bytes. The
fileReader
position is not moved.SystemError – If data could not be read from the
fileReader
.