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The function ‘builtins.match’ takes a POSIX extended regular
expression and an arbitrary string. It returns ‘null’ if the string
does not match the regular expression. Otherwise, it returns a list
containing substring matches corresponding to parenthesis groups in
the regex. The regex must match the entire string (i.e. there is an
implied "^<pat>$" around the regex). For example:
match "foo" "foobar" => null
match "foo" "foo" => []
match "f(o+)(.*)" "foooobar" => ["oooo" "bar"]
match "(.*/)?([^/]*)" "/dir/file.nix" => ["/dir/" "file.nix"]
match "(.*/)?([^/]*)" "file.nix" => [null "file.nix"]
The following example finds all regular files with extension .nix or
.patch underneath the current directory:
let
findFiles = pat: dir: concatLists (mapAttrsToList (name: type:
if type == "directory" then
findFiles pat (dir + "/" + name)
else if type == "regular" && match pat name != null then
[(dir + "/" + name)]
else []) (readDir dir));
in findFiles ".*\\.(nix|patch)" (toString ./.)
50 lines
1.4 KiB
C++
50 lines
1.4 KiB
C++
#include "regex.hh"
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#include "types.hh"
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#include <algorithm>
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namespace nix {
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Regex::Regex(const string & pattern, bool subs)
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{
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/* Patterns must match the entire string. */
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int err = regcomp(&preg, ("^(" + pattern + ")$").c_str(), (subs ? 0 : REG_NOSUB) | REG_EXTENDED);
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if (err) throw RegexError(format("compiling pattern ‘%1%’: %2%") % pattern % showError(err));
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nrParens = subs ? std::count(pattern.begin(), pattern.end(), '(') : 0;
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}
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Regex::~Regex()
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{
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regfree(&preg);
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}
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bool Regex::matches(const string & s)
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{
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int err = regexec(&preg, s.c_str(), 0, 0, 0);
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if (err == 0) return true;
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else if (err == REG_NOMATCH) return false;
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throw Error(format("matching string ‘%1%’: %2%") % s % showError(err));
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}
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bool Regex::matches(const string & s, Subs & subs)
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{
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regmatch_t pmatch[nrParens + 2];
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int err = regexec(&preg, s.c_str(), nrParens + 2, pmatch, 0);
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if (err == 0) {
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for (unsigned int n = 2; n < nrParens + 2; ++n)
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if (pmatch[n].rm_eo != -1)
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subs[n - 2] = string(s, pmatch[n].rm_so, pmatch[n].rm_eo - pmatch[n].rm_so);
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return true;
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}
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else if (err == REG_NOMATCH) return false;
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throw Error(format("matching string ‘%1%’: %2%") % s % showError(err));
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}
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string Regex::showError(int err)
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{
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char buf[256];
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regerror(err, &preg, buf, sizeof(buf));
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return string(buf);
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}
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}
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