PCRE2TEST(1) General Commands Manual PCRE2TEST(1) NAME pcre2test - a program for testing Perl-compatible regular expressions. SYNOPSIS pcre2test [options] [input file [output file]] pcre2test is a test program for the PCRE2 regular expression libraries, but it can also be used for experimenting with regular expressions. This document describes the features of the test program; for details of the regular expressions themselves, see the pcre2pattern documenta- tion. For details of the PCRE2 library function calls and their options, see the pcre2api documentation. The input for pcre2test is a sequence of regular expression patterns and subject strings to be matched. The output shows the result of each match attempt. Modifiers on the command line, the patterns, and the subject lines specify PCRE2 function options, control how the subject is processed, and what output is produced. As the original fairly simple PCRE library evolved, it acquired many different features, and as a result, the original pcretest program ended up with a lot of options in a messy, arcane syntax, for testing all the features. The move to the new PCRE2 API provided an opportunity to re-implement the test program as pcre2test, with a cleaner modifier syntax. Nevertheless, there are still many obscure modifiers, some of which are specifically designed for use in conjunction with the test script and data files that are distributed as part of PCRE2. All the modifiers are documented here, some without much justification, but many of them are unlikely to be of use except when testing the libraries. PCRE2's 8-BIT, 16-BIT AND 32-BIT LIBRARIES Different versions of the PCRE2 library can be built to support charac- ter strings that are encoded in 8-bit, 16-bit, or 32-bit code units. One, two, or all three of these libraries may be simultaneously installed. The pcre2test program can be used to test all the libraries. However, its own input and output are always in 8-bit format. When testing the 16-bit or 32-bit libraries, patterns and subject strings are converted to 16- or 32-bit format before being passed to the library functions. Results are converted back to 8-bit code units for output. In the rest of this document, the names of library functions and struc- tures are given in generic form, for example, pcre_compile(). The actual names used in the libraries have a suffix _8, _16, or _32, as appropriate. INPUT ENCODING Input to pcre2test is processed line by line, either by calling the C library's fgets() function, or via the libreadline library (see below). In Unix-like environments, fgets() treats any bytes other than newline as data characters. However, in some Windows environments character 26 (hex 1A) causes an immediate end of file, and no further data is read. For maximum portability, therefore, it is safest to avoid non-printing characters in pcre2test input files. COMMAND LINE OPTIONS -8 If the 8-bit library has been built, this option causes it to be used (this is the default). If the 8-bit library has not been built, this option causes an error. -16 If the 16-bit library has been built, this option causes it to be used. If only the 16-bit library has been built, this is the default. If the 16-bit library has not been built, this option causes an error. -32 If the 32-bit library has been built, this option causes it to be used. If only the 32-bit library has been built, this is the default. If the 32-bit library has not been built, this option causes an error. -b Behave as if each pattern has the /fullbincode modifier; the full internal binary form of the pattern is output after com- pilation. -C Output the version number of the PCRE2 library, and all available information about the optional features that are included, and then exit with zero exit code. All other options are ignored. -C option Output information about a specific build-time option, then exit. This functionality is intended for use in scripts such as RunTest. The following options output the value and set the exit code as indicated: ebcdic-nl the code for LF (= NL) in an EBCDIC environment: 0x15 or 0x25 0 if used in an ASCII environment exit code is always 0 linksize the configured internal link size (2, 3, or 4) exit code is set to the link size newline the default newline setting: CR, LF, CRLF, ANYCRLF, or ANY exit code is always 0 bsr the default setting for what \R matches: ANYCRLF or ANY exit code is always 0 The following options output 1 for true or 0 for false, and set the exit code to the same value: ebcdic compiled for an EBCDIC environment jit just-in-time support is available pcre16 the 16-bit library was built pcre32 the 32-bit library was built pcre8 the 8-bit library was built unicode Unicode support is available If an unknown option is given, an error message is output; the exit code is 0. -d Behave as if each pattern has the debug modifier; the inter- nal form and information about the compiled pattern is output after compilation; -d is equivalent to -b -i. -dfa Behave as if each subject line has the dfa modifier; matching is done using the pcre2_dfa_match() function instead of the default pcre2_match(). -help Output a brief summary these options and then exit. -i Behave as if each pattern has the /info modifier; information about the compiled pattern is given after compilation. -jit Behave as if each pattern line has the jit modifier; after successful compilation, each pattern is passed to the just- in-time compiler, if available. -pattern modifier-list Behave as if each pattern line contains the given modifiers. -q Do not output the version number of pcre2test at the start of execution. -S size On Unix-like systems, set the size of the run-time stack to size megabytes. -subject modifier-list Behave as if each subject line contains the given modifiers. -t Run each compile and match many times with a timer, and out- put the resulting times per compile or match. You can control the number of iterations that are used for timing by follow- ing -t with a number (as a separate item on the command line). For example, "-t 1000" iterates 1000 times. The default is to iterate 500,000 times. -tm This is like -t except that it times only the matching phase, not the compile phase. -T -TM These behave like -t and -tm, but in addition, at the end of a run, the total times for all compiles and matches are out- put. -version Output the PCRE2 version number and then exit. DESCRIPTION If pcre2test is given two filename arguments, it reads from the first and writes to the second. If it is given only one filename argument, it reads from that file and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and prompts for each line of input, using "re>" to prompt for regular expression patterns, and "data>" to prompt for subject lines. When pcre2test is built, a configuration option can specify that it should be linked with the libreadline or libedit library. When this is done, if the input is from a terminal, it is read using the readline() function. This provides line-editing and history facilities. The output from the -help option states whether or not readline() will be used. The program handles any number of tests, each of which consists of a set of input lines. Each set starts with a regular expression pattern, followed by any number of subject lines to be matched against that pat- tern. In between sets of test data, command lines that begin with a hash (#) character may appear. This file format, with some restric- tions, can also be processed by the perltest.pl script that is distrib- uted with PCRE2 as a means of checking that the behaviour of PCRE2 and Perl is the same. Each subject line is matched separately and independently. If you want to do multi-line matches, you have to use the \n escape sequence (or \r or \r\n, etc., depending on the newline setting) in a single line of input to encode the newline sequences. There is no limit on the length of subject lines; the input buffer is automatically extended if it is too small. There is a replication feature that makes it possible to generate long subject lines without having to supply them explicitly. An empty line or the end of the file signals the end of the subject lines for a test, at which point a new pattern or command line is expected if there is still input to be read. COMMAND LINES In between sets of test data, a line that begins with a hash (#) char- acter is interpreted as a command line. If the first character is fol- lowed by white space or an exclamation mark, the line is treated as a comment, and ignored. Otherwise, the following commands are recog- nized: #forbid_utf Subsequent patterns automatically have the PCRE2_NEVER_UTF and PCRE2_NEVER_UCP options set, which locks out the use of UTF and Unicode property features. This is a trigger guard that is used in test files to ensure that UTF/Unicode tests are not accidentally added to files that are used when UTF support is not included in the library. This effect can also be obtained by the use of #pattern; the difference is that #forbid_utf cannot be unset, and the automatic options are not displayed in pattern information, to avoid cluttering up test output. #pattern This command sets a default modifier list that applies to all subse- quent patterns. Modifiers on a pattern can change these settings. #perltest The appearance of this line causes all subsequent modifier settings to be checked for compatibility with the perltest.pl script, which is used to confirm that Perl gives the same results as PCRE2. Also, apart from comment lines, none of the other command lines are permitted, because they and many of the modifiers are specific to pcre2test, and should not be used in test files that are also processed by perltest.pl. The #perltest command helps detect tests that are accidentally put in the wrong file. #subject This command sets a default modifier list that applies to all subse- quent subject lines. Modifiers on a subject line can change these set- tings. MODIFIER SYNTAX Modifier lists are used with both pattern and subject lines. Items in a list are separated by commas and optional white space. Some modifiers may be given for both patterns and subject lines, whereas others are valid for one or the other only. Each modifier has a long name, for example "anchored", and some of them must be followed by an equals sign and a value, for example, "offset=12". Modifiers that do not take val- ues may be preceded by a minus sign to turn off a previous default set- ting. A few of the more common modifiers can also be specified as single let- ters, for example "i" for "caseless". In documentation, following the Perl convention, these are written with a slash ("the /i modifier") for clarity. Abbreviated modifiers must all be concatenated in the first item of a modifier list. If the first item is not recognized as a long modifier name, it is interpreted as a sequence of these abbreviations. For example: /abc/ig,newline=cr,jit=3 This is a pattern line whose modifier list starts with two one-letter modifiers (/i and /g). The lower-case abbreviated modifiers are the same as used in Perl. PATTERN SYNTAX A pattern line must start with one of the following characters (common symbols, excluding pattern meta-characters): / ! " ' ` - = _ : ; , % & @ ~ This is interpreted as the pattern's delimiter. A regular expression may be continued over several input lines, in which case the newline characters are included within it. It is possible to include the delim- iter within the pattern by escaping it with a backslash, for example /abc\/def/ If you do this, the escape and the delimiter form part of the pattern, but since the delimiters are all non-alphanumeric, this does not affect its interpretation. If the terminating delimiter is immediately fol- lowed by a backslash, for example, /abc/\ then a backslash is added to the end of the pattern. This is done to provide a way of testing the error condition that arises if a pattern finishes with a backslash, because /abc\/ is interpreted as the first line of a pattern that starts with "abc/", causing pcre2test to read the next line as a continuation of the regu- lar expression. A pattern can be followed by a modifier list (details below). SUBJECT LINE SYNTAX Before each subject line is passed to pcre2_match() or pcre2_dfa_match(), leading and trailing white space is removed, and the line is scanned for backslash escapes. The following provide a means of encoding non-printing characters in a visible way: \a alarm (BEL, \x07) \b backspace (\x08) \e escape (\x27) \f form feed (\x0c) \n newline (\x0a) \r carriage return (\x0d) \t tab (\x09) \v vertical tab (\x0b) \nnn octal character (up to 3 octal digits); always a byte unless > 255 in UTF-8 or 16-bit or 32-bit mode \o{dd...} octal character (any number of octal digits} \xhh hexadecimal byte (up to 2 hex digits) \x{hh...} hexadecimal character (any number of hex digits) The use of \x{hh...} is not dependent on the use of the utf modifier on the pattern. It is recognized always. There may be any number of hexa- decimal digits inside the braces; invalid values provoke error mes- sages. Note that \xhh specifies one byte rather than one character in UTF-8 mode; this makes it possible to construct invalid UTF-8 sequences for testing purposes. On the other hand, \x{hh} is interpreted as a UTF-8 character in UTF-8 mode, generating more than one byte if the value is greater than 127. When testing the 8-bit library not in UTF-8 mode, \x{hh} generates one byte for values less than 256, and causes an error for greater values. In UTF-16 mode, all 4-digit \x{hhhh} values are accepted. This makes it possible to construct invalid UTF-16 sequences for testing purposes. In UTF-32 mode, all 4- to 8-digit \x{...} values are accepted. This makes it possible to construct invalid UTF-32 sequences for testing purposes. There is a special backslash sequence that specifies replication of one or more characters: \[]{} This makes it possible to test long strings without having to provide them as part of the file. For example: \[abc]{4} is converted to "abcabcabcabc". This feature does not support nesting. To include a closing square bracket in the characters, code it as \x5D. A backslash followed by an equals sign marke the end of the subject string and the start of a modifier list. For example: abc\=notbol,notempty A backslash followed by any other non-alphanumeric character just escapes that character. A backslash followed by anything else causes an error. However, if the very last character in the line is a backslash (and there is no modifier list), it is ignored. This gives a way of passing an empty line as data, since a real empty line terminates the data input. PATTERN MODIFIERS There are three types of modifier that can appear in pattern lines, two of which may also be used in a #pattern command. A pattern's modifier list can add to or override default modifiers that were set by a previ- ous #pattern command. Setting compilation options The following modifiers set options for pcre2_compile(). The most com- mon ones have single-letter abbreviations. See pcreapi for a descrip- tion of their effects. allow_empty_class set PCRE2_ALLOW_EMPTY_CLASS alt_bsux set PCRE2_ALT_BSUX anchored set PCRE2_ANCHORED auto_callout set PCRE2_AUTO_CALLOUT /i caseless set PCRE2_CASELESS dollar_endonly set PCRE2_DOLLAR_ENDONLY /s dotall set PCRE2_DOTALL dupnames set PCRE2_DUPNAMES /x extended set PCRE2_EXTENDED firstline set PCRE2_FIRSTLINE match_unset_backref set PCRE2_MATCH_UNSET_BACKREF /m multiline set PCRE2_MULTILINE never_ucp set PCRE2_NEVER_UCP never_utf set PCRE2_NEVER_UTF no_auto_capture set PCRE2_NO_AUTO_CAPTURE no_auto_possess set PCRE2_NO_AUTO_POSSESS no_start_optimize set PCRE2_NO_START_OPTIMIZE no_utf_check set PCRE2_NO_UTF_CHECK ucp set PCRE2_UCP ungreedy set PCRE2_UNGREEDY utf set PCRE2_UTF As well as turning on the PCRE2_UTF option, the utf modifier causes all non-printing characters in output strings to be printed using the \x{hh...} notation. Otherwise, those less than 0x100 are output in hex without the curly brackets. Setting compilation controls The following modifiers affect the compilation process or request information about the pattern: bsr=[anycrlf|unicode] specify \R handling /B bincode show binary code without lengths debug same as info,fullbincode fullbincode show binary code with lengths /I info show info about compiled pattern hex pattern is coded in hexadecimal jit[=] use JIT jitverify verify JIT use locale= use this locale memory show memory used newline= set newline type parens_nest_limit= set maximum parentheses depth perlcompat lock out non-Perl modifiers posix use the POSIX API stackguard= test the stackguard feature tables=[0|1|2] select internal tables use_length use the pattern's length The effects of these modifiers are described in the following sections. FIXME: Give more examples. Newline and \R handling The bsr modifier specifies what \R in a pattern should match. If it is set to "anycrlf", \R matches CR, LF, or CRLF only. If it is set to "unicode", \R matches any Unicode newline sequence. The default is specified when PCRE2 is built, with the default default being Unicode. The newline modifier specifies which characters are to be interpreted as newlines, both in the pattern and (by default) in subject lines. The type must be one of CR, LF, CRLF, ANYCRLF, or ANY. Information about a pattern The debug modifier is a shorthand for info,fullbincode, requesting all available information. The bincode modifier causes a representation of the compiled code to be output after compilation. This information does not contain length and offset values, which ensures that the same output is generated for dif- ferent internal link sizes and different code unit widths. By using bincode, the same regression tests can be used in different environ- ments. The fullbincode modifier, by contrast, does include length and offset values. This is used in a few special tests and is also useful for one- off tests. The info modifier requests information about the compiled pattern (whether it is anchored, has a fixed first character, and so on). The information is obtained from the pcre2_pattern_info() function. Specifying a pattern in hex The hex modifier specifies that the characters of the pattern are to be interpreted as pairs of hexadecimal digits. White space is permitted between pairs. For example: /ab 32 59/hex This feature is provided as a way of creating patterns that contain binary zero characters. When hex is set, it implies use_length. Using the pattern's length By default, pcre2test passes patterns as zero-terminated strings to pcre2_compile(), giving the length as -1. If use_length is set, the length of the pattern is passed. This is implied if hex is set. JIT compilation The /jit modifier may optionally be followed by and equals sign and a number in the range 0 to 7: 0 disable JIT 1 use JIT for normal match only 2 use JIT for soft partial match only 3 use JIT for normal match and soft partial match 4 use JIT for hard partial match only 6 use JIT for soft and hard partial match 7 all three modes If no number is given, 7 is assumed. If JIT compilation is successful, the compiled JIT code will automatically be used when pcre2_match() is run for the appropriate type of match, except when incompatible run- time options are specified. For more details, see the pcre2jit documen- tation. See also the jitstack modifier below for a way of setting the size of the JIT stack. If the jitverify modifier is specified, information about the compiled pattern shows whether JIT compilation was or was not successful. If jitverify is specified without jit, jit=7 is assumed. If JIT compila- tion is successful when jitverify is set, the text "(JIT)" is added to the first output line after a match or non match when JIT-compiled code was actually used. Setting a locale The /locale modifier must specify the name of a locale, for example: /pattern/locale=fr_FR The given locale is set, pcre2_maketables() is called to build a set of character tables for the locale, and this is then passed to pcre2_com- pile() when compiling the regular expression. The same tables are used when matching the following subject lines. The /locale modifier applies only to the pattern on which it appears, but can be given in a #pattern command if a default is needed. Setting a locale and alternate charac- ter tables are mutually exclusive. Showing pattern memory The /memory modifier causes the size in bytes of the memory block used to hold the compiled pattern to be output. This does not include the size of the pcre2_code block; it is just the actual compiled data. If the pattern is subsequently passed to the JIT compiler, the size of the JIT compiled code is also output. Limiting nested parentheses The parens_nest_limit modifier sets a limit on the depth of nested parentheses in a pattern. Breaching the limit causes a compilation error. Using the POSIX wrapper API The /posix modifier causes pcre2test to call PCRE2 via the POSIX wrap- per API rather than its native API. This supports only the 8-bit library. When the POSIX API is being used, the following pattern modi- fiers set options for the regcomp() function: caseless REG_ICASE multiline REG_NEWLINE no_auto_capture REG_NOSUB dotall REG_DOTALL ) ungreedy REG_UNGREEDY ) These options are not part of ucp REG_UCP ) the POSIX standard utf REG_UTF8 ) The aftertext and allaftertext subject modifiers work as described below. All other modifiers cause an error. Testing the stack guard feature The /stackguard modifier is used to test the use of pcre2_set_com- pile_recursion_guard(), a function that is provided to enable stack availability to be checked during compilation (see the pcre2api docu- mentation for details). If the number specified by the modifier is greater than zero, pcre2_set_compile_recursion_guard() is called to set up callback from pcre2_compile() to a local function. The argument it is passed is the current nesting parenthesis depth; if this is greater than the value given by the modifier, non-zero is returned, causing the compilation to be aborted. Using alternative character tables The /tables modifier must be followed by a single digit. It causes a specific set of built-in character tables to be passed to pcre2_com- pile(). This is used in the PCRE2 tests to check behaviour with differ- ent character tables. The digit specifies the tables as follows: 0 do not pass any special character tables 1 the default ASCII tables, as distributed in pcre2_chartables.c.dist 2 a set of tables defining ISO 8859 characters In table 2, some characters whose codes are greater than 128 are iden- tified as letters, digits, spaces, etc. Setting alternate character tables and a locale are mutually exclusive. Setting certain match controls The following modifiers are really subject modifiers, and are described below. However, they may be included in a pattern's modifier list, in which case they are applied to every subject line that is processed with that pattern. They do not affect the compilation process. aftertext show text after match allaftertext show text after captures allcaptures show all captures allusedtext show all consulted text /g global global matching mark show mark values These modifiers may not appear in a #pattern command. If you want them as defaults, set them in a #subject command. SUBJECT MODIFIERS The modifiers that can appear in subject lines and the #subject command are of two types. Setting match options The following modifiers set options for pcre2_match() or pcre2_dfa_match(). See pcreapi for a description of their effects. anchored set PCRE2_ANCHORED dfa_restart set PCRE2_DFA_RESTART dfa_shortest set PCRE2_DFA_SHORTEST no_utf_check set PCRE2_NO_UTF_CHECK notbol set PCRE2_NOTBOL notempty set PCRE2_NOTEMPTY notempty_atstart set PCRE2_NOTEMPTY_ATSTART noteol set PCRE2_NOTEOL partial_hard (or ph) set PCRE2_PARTIAL_HARD partial_soft (or ps) set PCRE2_PARTIAL_SOFT The partial matching modifiers are provided with abbreviations because they appear frequently in tests. If the /posix modifier was present on the pattern, causing the POSIX wrapper API to be used, the only option-setting modifiers that have any effect are notbol, notempty, and noteol, causing REG_NOTBOL, REG_NOTEMPTY, and REG_NOTEOL, respectively, to be passed to regexec(). Any other modifiers cause an error. Setting match controls The following modifiers affect the matching process or request addi- tional information. Some of them may also be specified on a pattern line (see above), in which case they apply to every subject line that is matched against that pattern. aftertext show text after match allaftertext show text after captures allcaptures show all captures allusedtext show all consulted text (non-JIT only) altglobal alternative global matching callout_capture show captures at callout time callout_data= set a value to pass via callouts callout_fail=[:] control callout failure callout_none do not supply a callout function copy= copy captured substring dfa use pcre2_dfa_match() find_limits find match and recursion limits get= extract captured substring getall extract all captured substrings /g global global matching jitstack= set size of JIT stack mark show mark values match_limit=>n> set a match limit memory show memory usage offset= set starting offset ovector= set size of output vector recursion_limit= set a recursion limit The effects of these modifiers are described in the following sections. FIXME: Give more examples. Showing more text The aftertext modifier requests that as well as outputting the sub- string that matched the entire pattern, pcre2test should in addition output the remainder of the subject string. This is useful for tests where the subject contains multiple copies of the same substring. The allaftertext modifier requests the same action for captured substrings as well as the main matched substring. In each case the remainder is output on the following line with a plus character following the cap- ture number. The allusedtext modifier requests that all the text that was consulted during a successful pattern match by the interpreter should be shown. This feature is not supported for JIT matching, and if requested with JIT it is ignored (with a warning message). Setting this modifier affects the output if there is a lookbehind at the start of a match, or a lookahead at the end, or if \K is used in the pattern. Characters that precede or follow the start and end of the actual match are indi- cated in the output by '<' or '>' characters underneath them. Here is an example: /(?<=pqr)abc(?=xyz)/ 123pqrabcxyz456\=allusedtext 0: pqrabcxyz <<< >>> This shows that the matched string is "abc", with the preceding and following strings "pqr" and "xyz" also consulted during the match. Showing the value of all capture groups The allcaptures modifier requests that the values of all potential cap- tured parentheses be output after a match. By default, only those up to the highest one actually used in the match are output (corresponding to the return code from pcre2_match()). Groups that did not take part in the match are output as "". Testing callouts A callout function is supplied when pcre2test calls the library match- ing functions, unless callout_none is specified. If callout_capture is set, the current captured groups are output when a callout occurs. The callout_fail modifier can be given one or two numbers. If there is only one number, 1 is returned instead of 0 when a callout of that num- ber is reached. If two numbers are given, 1 is returned when callout is reached for the th time. The callout_data modifier can be given an unsigned or a negative num- ber. Any value other than zero is used as a return from pcre2test's callout function. Testing substring extraction functions The copy and get modifiers can be used to test the pcre2_sub- string_copy_xxx() and pcre2_substring_get_xxx() functions. They can be given more than once, and each can specify a group name or number, for example: abcd\=copy=1,copy=3,get=G1 If the #subject command is used to set default copy and get lists, these can be unset by specifying a negative number for numbered groups and an empty name for named groups. The getall modifier tests pcre2_substring_list_get(), which extracts all captured substrings. If the subject line is successfully matched, the substrings extracted by the convenience functions are output with C, G, or L after the string number instead of a colon. This is in addition to the normal full list. The string length (that is, the return from the extraction function) is given in parentheses after each substring. Finding all matches in a string Searching for all possible matches within a subject can be requested by the global or /altglobal modifier. After finding a match, the matching function is called again to search the remainder of the subject. The difference between global and altglobal is that the former uses the start_offset argument to pcre2_match() or pcre2_dfa_match() to start searching at a new point within the entire string (which is what Perl does), whereas the latter passes over a shortened substring. This makes a difference to the matching process if the pattern begins with a look- behind assertion (including \b or \B). If an empty string is matched, the next match is done with the PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED flags set, in order to search for another, non-empty, match at the same point in the subject. If this match fails, the start offset is advanced, and the normal match is retried. This imitates the way Perl handles such cases when using the /g modifier or the split() function. Normally, the start offset is advanced by one character, but if the newline convention recognizes CRLF as a newline, and the current character is CR followed by LF, an advance of two is used. Setting the JIT stack size The jitstack modifier provides a way of setting the maximum stack size that is used by the just-in-time optimization code. It is ignored if JIT optimization is not being used. Providing a stack that is larger than the default 32K is necessary only for very complicated patterns. Setting match and recursion limits The match_limit and recursion_limit modifiers set the appropriate lim- its in the match context. These values are ignored when the find_limits modifier is specified. Finding minimum limits If the find_limits modifier is present, pcre2test calls pcre2_match() several times, setting different values in the match context via pcre2_set_match_limit() and pcre2_set_recursion_limit() until it finds the minimum values for each parameter that allow pcre2_match() to com- plete without error. If JIT is being used, only the match limit is relevant. If DFA matching is being used, neither limit is relevant, and this modifier is ignored (with a warning message). The match_limit number is a measure of the amount of backtracking that takes place, and learning the minimum value can be instructive. For most simple matches, the number is quite small, but for patterns with very large numbers of matching possibilities, it can become large very quickly with increasing length of subject string. The match_limit_recursion number is a measure of how much stack (or, if PCRE2 is compiled with NO_RECURSE, how much heap) memory is needed to complete the match attempt. Showing MARK names The mark modifier causes the names from backtracking control verbs that are returned from calls to pcre2_match() to be displayed. If a mark is returned for a match, non-match, or partial match, pcre2test shows it. For a match, it is on a line by itself, tagged with "MK:". Otherwise, it is added to the non-match message. Showing memory usage The memory modifier causes pcre2test to log all memory allocation and freeing calls that occur during a match operation. Setting a starting offset The offset modifier sets an offset in the subject string at which matching starts. Its value is a number of code units, not characters. Setting the size of the output vector The ovector modifier applies only to the subject line in which it appears, though of course it can also be used to set a default in a #subject command. It specifies the number of pairs of offsets that are available for storing matching information. The default is 15. At least one pair of offsets is always created by pcre2_match_data_cre- ate(), for matching with PCRE2's native API, so a value of 0 is the same as 1. However a value of 0 is useful when testing the POSIX API because it causes regexec() to be called with a NULL capture vector. THE ALTERNATIVE MATCHING FUNCTION By default, pcre2test uses the standard PCRE2 matching function, pcre2_match() to match each subject line. PCRE2 also supports an alter- native matching function, pcre2_dfa_match(), which operates in a dif- ferent way, and has some restrictions. The differences between the two functions are described in the pcre2matching documentation. If the dfa modifier is set, the alternative matching function is used. This function finds all possible matches at a given point in the sub- ject. If, however, the dfa_shortest modifier is set, processing stops after the first match is found. This is always the shortest possible match. DEFAULT OUTPUT FROM pcre2test This section describes the output when the normal matching function, pcre2_match(), is being used. When a match succeeds, pcre2test outputs the list of captured sub- strings, starting with number 0 for the string that matched the whole pattern. Otherwise, it outputs "No match" when the return is PCRE2_ERROR_NOMATCH, or "Partial match:" followed by the partially matching substring when the return is PCRE2_ERROR_PARTIAL. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind assertion, \K, \b, or \B was involved.) For any other return, pcre2test outputs the PCRE2 negative error number and a short descriptive phrase. If the error is a failed UTF string check, the offset of the start of the failing character and the reason code are also output. Here is an example of an interactive pcre2test run. $ pcre2test PCRE2 version 9.00 2014-05-10 re> /^abc(\d+)/ data> abc123 0: abc123 1: 123 data> xyz No match Unset capturing substrings that are not followed by one that is set are not returned by pcre2_match(), and are not shown by pcre2test. In the following example, there are two capturing substrings, but when the first data line is matched, the second, unset substring is not shown. An "internal" unset substring is shown as "", as for the second data line. re> /(a)|(b)/ data> a 0: a 1: a data> b 0: b 1: 2: b If the strings contain any non-printing characters, they are output as \xhh escapes if the value is less than 256 and UTF mode is not set. Otherwise they are output as \x{hh...} escapes. See below for the defi- nition of non-printing characters. If the /aftertext modifier is set, the output for substring 0 is followed by the the rest of the subject string, identified by "0+" like this: re> /cat/aftertext data> cataract 0: cat 0+ aract If global matching is requested, the results of successive matching attempts are output in sequence, like this: re> /\Bi(\w\w)/g data> Mississippi 0: iss 1: ss 0: iss 1: ss 0: ipp 1: pp "No match" is output only if the first match attempt fails. Here is an example of a failure message (the offset 4 that is specified by \>4 is past the end of the subject string): re> /xyz/ data> xyz\=offset=4 Error -24 (bad offset value) Note that whereas patterns can be continued over several lines (a plain ">" prompt is used for continuations), subject lines may not. However newlines can be included in a subject by means of the \n escape (or \r, \r\n, etc., depending on the newline sequence setting). OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION When the alternative matching function, pcre2_dfa_match(), is used, the output consists of a list of all the matches that start at the first point in the subject where there is at least one match. For example: re> /(tang|tangerine|tan)/ data> yellow tangerine\=dfa 0: tangerine 1: tang 2: tan (Using the normal matching function on this data finds only "tang".) The longest matching string is always given first (and numbered zero). After a PCRE2_ERROR_PARTIAL return, the output is "Partial match:", followed by the partially matching substring. (Note that this is the entire substring that was inspected during the partial match; it may include characters before the actual match start if a lookbehind asser- tion, \K, \b, or \B was involved.) If global matching is requested, the search for further matches resumes at the end of the longest match. For example: re> /(tang|tangerine|tan)/g data> yellow tangerine and tangy sultana\=dfa 0: tangerine 1: tang 2: tan 0: tang 1: tan 0: tan The alternative matching function does not support substring capture, so the modifiers that are concerned with captured substrings are not relevant. RESTARTING AFTER A PARTIAL MATCH When the alternative matching function has given the PCRE2_ERROR_PAR- TIAL return, indicating that the subject partially matched the pattern, you can restart the match with additional subject data by means of the dfa_restart modifier. For example: re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/ data> 23ja\=P,dfa Partial match: 23ja data> n05\=dfa,dfa_restart 0: n05 For further information about partial matching, see the pcre2partial documentation. CALLOUTS If the pattern contains any callout requests, pcre2test's callout func- tion is called during matching. This works with both matching func- tions. By default, the called function displays the callout number, the start and current positions in the text at the callout time, and the next pattern item to be tested. For example: --->pqrabcdef 0 ^ ^ \d This output indicates that callout number 0 occurred for a match attempt starting at the fourth character of the subject string, when the pointer was at the seventh character, and when the next pattern item was \d. Just one circumflex is output if the start and current positions are the same. Callouts numbered 255 are assumed to be automatic callouts, inserted as a result of the /auto_callout pattern modifier. In this case, instead of showing the callout number, the offset in the pattern, preceded by a plus, is output. For example: re> /\d?[A-E]\*/auto_callout data> E* --->E* +0 ^ \d? +3 ^ [A-E] +8 ^^ \* +10 ^ ^ 0: E* If a pattern contains (*MARK) items, an additional line is output when- ever a change of latest mark is passed to the callout function. For example: re> /a(*MARK:X)bc/auto_callout data> abc --->abc +0 ^ a +1 ^^ (*MARK:X) +10 ^^ b Latest Mark: X +11 ^ ^ c +12 ^ ^ 0: abc The mark changes between matching "a" and "b", but stays the same for the rest of the match, so nothing more is output. If, as a result of backtracking, the mark reverts to being unset, the text "" is output. The callout function in pcre2test returns zero (carry on matching) by default, but you can use a callout_fail modifier in a subject line (as described above) to change this and other parameters of the callout. Inserting callouts can be helpful when using pcre2test to check compli- cated regular expressions. For further information about callouts, see the pcre2callout documentation. NON-PRINTING CHARACTERS When pcre2test is outputting text in the compiled version of a pattern, bytes other than 32-126 are always treated as non-printing characters and are therefore shown as hex escapes. When pcre2test is outputting text that is a matched part of a subject string, it behaves in the same way, unless a different locale has been set for the pattern (using the /locale modifier). In this case, the isprint() function is used to distinguish printing and non-printing characters. SEE ALSO pcre2(3), pcre16(3), pcre32(3), pcre2api(3), pcre2callout(3), pcre2jit, pcre2matching(3), pcre2partial(d), pcre2pattern(3), pcre2precompile(3). AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 11 October 2014 Copyright (c) 1997-2014 University of Cambridge.