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< p > The < a href = "http://www.lispworks.com/documentation/HyperSpec/index.html" > ANSI Common Lisp
standard< / a >
does not include facilities for regular expressions, but a couple of
libraries exist for this task, for instance:
< a href = "https://github.com/edicl/cl-ppcre" > cl-ppcre< / a > .< / p >
< p > See also the respective < a href = "http://www.cliki.net/Regular%20Expression" > Cliki:
regexp< / a > page for more
links.< / p >
< p > Note that some CL implementations include regexp facilities, notably
< a href = "http://clisp.sourceforge.net/impnotes.html#regexp" > CLISP< / a > and
< a href = "https://franz.com/support/documentation/current/doc/regexp.htm" > ALLEGRO
CL< / a > . If
in doubt, check your manual or ask your vendor.< / p >
< p > The description provided below is far from complete, so don’
to check the reference manual that comes along with the CL-PPCRE
library.< / p >
< h2 id = "ppcre" > PPCRE< / h2 >
< p > < a href = "https://github.com/edicl/cl-ppcre" > CL-PPCRE< / a > (abbreviation for
Portable Perl-compatible regular expressions) is a portable regular
expression library for Common Lisp with a broad set of features and
good performance. It has been ported to a number of Common Lisp
implementations and can be easily installed (or added as a dependency)
via Quicklisp:< / p >
< pre > < code class = "language-lisp" > (ql:quickload "cl-ppcre")
< / code > < / pre >
< p > Basic operations with the CL-PPCRE library functions are described
below.< / p >
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< h3 id = "looking-for-matching-patterns-scan-create-scanner" > Looking for matching patterns: scan, create-scanner< / h3 >
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< p > The < code > scan< / code > function tries to match the given pattern and on success
returns four multiple-values values - the start of the match, the end
of the match, and two arrays denoting the beginnings and ends of
register matches. On failure returns < code > NIL< / code > .< / p >
< p > A regular expression pattern can be compiled with the < code > create-scanner< / code >
function call. A “scanner” will be created that can be used by other
functions.< / p >
< p > For example:< / p >
< pre > < code class = "language-lisp" > (let ((ptrn (ppcre:create-scanner "(a)*b")))
(ppcre:scan ptrn "xaaabd"))
< / code > < / pre >
< p > will yield the same results as:< / p >
< pre > < code class = "language-lisp" > (ppcre:scan "(a)*b" "xaaabd")
< / code > < / pre >
< p > but will require less time for repeated < code > scan< / code > calls as parsing the
expression and compiling it is done only once.< / p >
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< h3 id = "extracting-information" > Extracting information< / h3 >
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< p > CL-PPCRE provides several ways to extract matching fragments.< / p >
< h4 id = "all-matches-all-matches-as-strings" > all-matches, all-matches-as-strings< / h4 >
< p > The function < code > all-matches-as-strings< / code > is very handy: it returns a list of matches:< / p >
< pre > < code class = "language-lisp" > (ppcre:all-matches-as-strings "\\d+" "numbers: 1 10 42")
;; => ("1" "10" "42")
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< / code > < / pre >
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< p > The function < code > all-matches< / code > is similar, but it returns a list of positions:< / p >
< pre > < code class = "language-lisp" > (ppcre:all-matches "\\d+" "numbers: 1 10 42")
;; => (9 10 11 13 14 16)
< / code > < / pre >
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< p > Look carefully: it actually return a list containing the start and end
positions of all matches: 9 and 10 are the start and end for the first
number (1), and so on.< / p >
< p > If you wanted to extract integers from this example string, simply map
< code > parse-integer< / code > to the result:< / p >
< pre > < code class = "language-lisp" > CL-USER> (ppcre:all-matches-as-strings "\\d+" "numbers: 1 10 42")
;; ("1" "10" "42")
CL-USER> (mapcar #'parse-integer *)
(1 10 42)
< / code > < / pre >
< p > The two functions accept the usual < code > :start< / code > and < code > :end< / code > key arguments. Additionnaly, < code > all-matches-as-strings< / code > accepts a < code > :sharedp< / code > argument:< / p >
< blockquote >
< p > If SHAREDP is true, the substrings may share structure with TARGET-STRING.< / p >
< / blockquote >
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< h4 id = "count-matches-new-in-212-april-2024" > count-matches (new in 2.1.2, April 2024)< / h4 >
< p > < code > (count-matches regex target-string)< / code > returns a count of all matches of < code > regex< / code > against < code > target-string< / code > :< / p >
< pre > < code class = "language-lisp" > CL-USER> (ppcre:count-matches "a" "foo bar baz")
2
CL-USER> (ppcre:count-matches "\\w*" "foo bar baz")
6
< / code > < / pre >
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< h4 id = "scan-to-strings-register-groups-bind" > scan-to-strings, register-groups-bind< / h4 >
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< p > The < code > scan-to-strings< / code > function is similar to < code > scan< / code > but returns
substrings of target-string instead of positions. This function
returns two values on success: the whole match as a string plus an
array of substrings (or NILs) corresponding to the matched registers.< / p >
< p > The < code > register-groups-bind< / code > function tries to match the given pattern
against the target string and binds matching fragments with the given
variables.< / p >
< pre > < code class = "language-lisp" > (ppcre:register-groups-bind (first second third fourth)
("((a)|(b)|(c))+" "abababc" :sharedp t)
(list first second third fourth))
;; => ("c" "a" "b" "c")
< / code > < / pre >
< p > CL-PPCRE also provides a shortcut for calling a function before
assigning the matching fragment to the variable:< / p >
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< pre > < code class = "language-lisp" > (ppcre:register-groups-bind
(fname lname (#'parse-integer date month year))
("(\\w+)\\s+(\\w+)\\s+(\\d{1,2})\\.(\\d{1,2})\\.(\\d{4})"
"Frank Zappa 21.12.1940")
(list fname lname date month year))
;; => ("Frank" "Zappa" 21 12 1940)
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< / code > < / pre >
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< h3 id = "replacing-text-regex-replace-regex-replace-all" > Replacing text: regex-replace, regex-replace-all< / h3 >
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< pre > < code class = "language-lisp" > (ppcre:regex-replace "a" "abc" "A") ;; => "Abc"
;; or
(let ((pat (ppcre:create-scanner "a")))
(ppcre:regex-replace pat "abc" "A"))
< / code > < / pre >
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< h2 id = "see-more" > See more< / h2 >
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< ul >
< li > < a href = "https://common-lisp-libraries.readthedocs.io/cl-ppcre/" > cl-ppcre on common-lisp-libraries.readthedocs.io< / a > and read on: < code > do-matches< / code > , < code > do-matches-as-strings< / code > ,
< code > do-register-groups< / code > , < code > do-scans< / code > , < code > parse-string< / code > , < code > regex-apropos< / code > ,
< code > quote-meta-chars< / code > , < code > split< / code > …< / li >
< / ul >
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< p class = "page-source" >
Page source: < a href = "https://github.com/LispCookbook/cl-cookbook/blob/master/regexp.md" > regexp.md< / a >
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