Provided by: pcre2-utils_10.34-7ubuntu0.1_amd64 
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 documentation. 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.
There are also command lines for setting defaults and controlling some special actions. The output shows
the result of each match attempt. Modifiers on external or internal command lines, 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 character 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-bit 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 structures 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. In some Windows environments character 26 (hex 1A) causes an immediate end of
file, and no further data is read, so this character should be avoided unless you really want that
action.
The input is processed using using C's string functions, so must not contain binary zeros, even though in
Unix-like environments, fgets() treats any bytes other than newline as data characters. An error is
generated if a binary zero is encountered. By default subject lines are processed for backslash escapes,
which makes it possible to include any data value in strings that are passed to the library for matching.
For patterns, there is a facility for specifying some or all of the 8-bit input characters as hexadecimal
pairs, which makes it possible to include binary zeros.
Input for the 16-bit and 32-bit libraries
When testing the 16-bit or 32-bit libraries, there is a need to be able to generate character code points
greater than 255 in the strings that are passed to the library. For subject lines, backslash escapes can
be used. In addition, when the utf modifier (see "Setting compilation options" below) is set, the pattern
and any following subject lines are interpreted as UTF-8 strings and translated to UTF-16 or UTF-32 as
appropriate.
For non-UTF testing of wide characters, the utf8_input modifier can be used. This is mutually exclusive
with utf, and is allowed only in 16-bit or 32-bit mode. It causes the pattern and following subject lines
to be treated as UTF-8 according to the original definition (RFC 2279), which allows for character values
up to 0x7fffffff. Each character is placed in one 16-bit or 32-bit code unit (in the 16-bit case, values
greater than 0xffff cause an error to occur).
UTF-8 (in its original definition) is not capable of encoding values greater than 0x7fffffff, but such
values can be handled by the 32-bit library. When testing this library in non-UTF mode with utf8_input
set, if any character is preceded by the byte 0xff (which is an invalid byte in UTF-8) 0x80000000 is
added to the character's value. This is the only way of passing such code points in a pattern string. For
subject strings, using an escape sequence is preferable.
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.
-ac Behave as if each pattern has the auto_callout modifier, that is, insert automatic callouts
into every pattern that is compiled.
-AC As for -ac, but in addition behave as if each subject line has the callout_extra modifier, that
is, show additional information from callouts.
-b Behave as if each pattern has the fullbincode modifier; the full internal binary form of the
pattern is output after compilation.
-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. If both -C and -LM are present, whichever is first is recognized.
-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, ANY, or NUL
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:
backslash-C \C is supported (not locked out)
ebcdic compiled for an EBCDIC environment
jit just-in-time support is available
pcre2-16 the 16-bit library was built
pcre2-32 the 32-bit library was built
pcre2-8 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 internal 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().
-error number[,number,...]
Call pcre2_get_error_message() for each of the error numbers in the comma-separated list,
display the resulting messages on the standard output, then exit with zero exit code. The
numbers may be positive or negative. This is a convenience facility for PCRE2 maintainers.
-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.
-jitfast Behave as if each pattern line has the jitfast modifier; after successful compilation, each
pattern is passed to the just-in-time compiler, if available, and each subject line is passed
directly to the JIT matcher via its "fast path".
-jitverify
Behave as if each pattern line has the jitverify modifier; after successful compilation, each
pattern is passed to the just-in-time compiler, if available, and the use of JIT for matching
is verified.
-LM List modifiers: write a list of available pattern and subject modifiers to the standard output,
then exit with zero exit code. All other options are ignored. If both -C and -LM are present,
whichever is first is recognized.
-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 mebibytes (units of 1024*1024
bytes).
-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 output the resulting times per compile
or match. When JIT is used, separate times are given for the initial compile and the JIT
compile. You can control the number of iterations that are used for timing by following -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 output.
-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 the
first name is "-", input is taken from the standard input. If pcre2test is given only one argument, it
reads from that file and writes to stdout. Otherwise, it reads from stdin and writes to stdout.
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
pattern. In between sets of test data, command lines that begin with # may appear. This file format, with
some restrictions, can also be processed by the perltest.sh script that is distributed with PCRE2 as a
means of checking that the behaviour of PCRE2 and Perl is the same. For a specification of perltest.sh,
see the comments near its beginning.
When the input is a terminal, pcre2test prompts for each line of input, using "re>" to prompt for regular
expression patterns, and "data>" to prompt for subject lines. Command lines starting with # can be
entered only in response to the "re>" prompt.
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 are replication features that makes it possible to
generate long repetitive pattern or 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 # is interpreted as a command line. If the first
character is followed by white space or an exclamation mark, the line is treated as a comment, and
ignored. Otherwise, the following commands are recognized:
#forbid_utf
Subsequent patterns automatically have the PCRE2_NEVER_UTF and PCRE2_NEVER_UCP options set, which locks
out the use of the PCRE2_UTF and PCRE2_UCP options and the use of (*UTF) and (*UCP) at the start of
patterns. This command also forces an error if a subsequent pattern contains any occurrences of \P, \p,
or \X, which are still supported when PCRE2_UTF is not set, but which require Unicode property support to
be included in the library.
This is a trigger guard that is used in test files to ensure that UTF or Unicode property tests are not
accidentally added to files that are used when Unicode support is not included in the library. Setting
PCRE2_NEVER_UTF and PCRE2_NEVER_UCP as a default 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.
#load <filename>
This command is used to load a set of precompiled patterns from a file, as described in the section
entitled "Saving and restoring compiled patterns" below.
#newline_default [<newline-list>]
When PCRE2 is built, a default newline convention can be specified. This determines which characters
and/or character pairs are recognized as indicating a newline in a pattern or subject string. The default
can be overridden when a pattern is compiled. The standard test files contain tests of various newline
conventions, but the majority of the tests expect a single linefeed to be recognized as a newline by
default. Without special action the tests would fail when PCRE2 is compiled with either CR or CRLF as the
default newline.
The #newline_default command specifies a list of newline types that are acceptable as the default. The
types must be one of CR, LF, CRLF, ANYCRLF, ANY, or NUL (in upper or lower case), for example:
#newline_default LF Any anyCRLF
If the default newline is in the list, this command has no effect. Otherwise, except when testing the
POSIX API, a newline modifier that specifies the first newline convention in the list (LF in the above
example) is added to any pattern that does not already have a newline modifier. If the newline list is
empty, the feature is turned off. This command is present in a number of the standard test input files.
When the POSIX API is being tested there is no way to override the default newline convention, though it
is possible to set the newline convention from within the pattern. A warning is given if the posix or
posix_nosub modifier is used when #newline_default would set a default for the non-POSIX API.
#pattern <modifier-list>
This command sets a default modifier list that applies to all subsequent 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.sh script, which is used to confirm that Perl gives the same results as PCRE2. Also, apart
from comment lines, #pattern commands, and #subject commands that set or unset "mark", no 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.sh. The #perltest command helps detect tests that are
accidentally put in the wrong file.
#pop [<modifiers>]
#popcopy [<modifiers>]
These commands are used to manipulate the stack of compiled patterns, as described in the section
entitled "Saving and restoring compiled patterns" below.
#save <filename>
This command is used to save a set of compiled patterns to a file, as described in the section entitled
"Saving and restoring compiled patterns" below.
#subject <modifier-list>
This command sets a default modifier list that applies to all subsequent subject lines. Modifiers on a
subject line can change these settings.
MODIFIER SYNTAX
Modifier lists are used with both pattern and subject lines. Items in a list are separated by commas
followed by optional white space. Trailing whitespace in a modifier list is ignored. Some modifiers may
be given for both patterns and subject lines, whereas others are valid only for one or the other. 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". Values cannot contain comma characters, but may contain spaces.
Modifiers that do not take values may be preceded by a minus sign to turn off a previous setting.
A few of the more common modifiers can also be specified as single letters, 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
delimiter 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
followed 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 regular 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, unless the subject_literal modifier was
set for the pattern. 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 hexadecimal digits inside the braces; invalid values provoke error
messages.
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:
\[<characters>]{<count>}
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 marks the end of the subject string and the start of a modifier
list. For example:
abc\=notbol,notempty
If the subject string is empty and \= is followed by whitespace, the line is treated as a comment line,
and is not used for matching. For example:
\= This is a comment.
abc\= This is an invalid modifier list.
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.
If the subject_literal modifier is set for a pattern, all subject lines that follow are treated as
literals, with no special treatment of backslashes. No replication is possible, and any subject
modifiers must be set as defaults by a #subject command.
PATTERN MODIFIERS
There are several types of modifier that can appear in pattern lines. Except where noted below, they may
also be used in #pattern commands. A pattern's modifier list can add to or override default modifiers
that were set by a previous #pattern command.
Setting compilation options
The following modifiers set options for pcre2_compile(). Most of them set bits in the options argument of
that function, but those whose names start with PCRE2_EXTRA are additional options that are set in the
compile context. For the main options, there are some single-letter abbreviations that are the same as
Perl options. There is special handling for /x: if a second x is present, PCRE2_EXTENDED is converted
into PCRE2_EXTENDED_MORE as in Perl. A third appearance adds PCRE2_EXTENDED as well, though this makes no
difference to the way pcre2_compile() behaves. See pcre2api for a description of the effects of these
options.
allow_empty_class set PCRE2_ALLOW_EMPTY_CLASS
allow_surrogate_escapes set PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES
alt_bsux set PCRE2_ALT_BSUX
alt_circumflex set PCRE2_ALT_CIRCUMFLEX
alt_verbnames set PCRE2_ALT_VERBNAMES
anchored set PCRE2_ANCHORED
auto_callout set PCRE2_AUTO_CALLOUT
bad_escape_is_literal set PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
/i caseless set PCRE2_CASELESS
dollar_endonly set PCRE2_DOLLAR_ENDONLY
/s dotall set PCRE2_DOTALL
dupnames set PCRE2_DUPNAMES
endanchored set PCRE2_ENDANCHORED
escaped_cr_is_lf set PCRE2_EXTRA_ESCAPED_CR_IS_LF
/x extended set PCRE2_EXTENDED
/xx extended_more set PCRE2_EXTENDED_MORE
extra_alt_bsux set PCRE2_EXTRA_ALT_BSUX
firstline set PCRE2_FIRSTLINE
literal set PCRE2_LITERAL
match_line set PCRE2_EXTRA_MATCH_LINE
match_invalid_utf set PCRE2_MATCH_INVALID_UTF
match_unset_backref set PCRE2_MATCH_UNSET_BACKREF
match_word set PCRE2_EXTRA_MATCH_WORD
/m multiline set PCRE2_MULTILINE
never_backslash_c set PCRE2_NEVER_BACKSLASH_C
never_ucp set PCRE2_NEVER_UCP
never_utf set PCRE2_NEVER_UTF
/n no_auto_capture set PCRE2_NO_AUTO_CAPTURE
no_auto_possess set PCRE2_NO_AUTO_POSSESS
no_dotstar_anchor set PCRE2_NO_DOTSTAR_ANCHOR
no_start_optimize set PCRE2_NO_START_OPTIMIZE
no_utf_check set PCRE2_NO_UTF_CHECK
ucp set PCRE2_UCP
ungreedy set PCRE2_UNGREEDY
use_offset_limit set PCRE2_USE_OFFSET_LIMIT
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 utf in 16-bit or 32-bit mode also causes pattern and subject strings
to be translated to UTF-16 or UTF-32, respectively, before being passed to library functions.
Setting compilation controls
The following modifiers affect the compilation process or request information about the pattern. There
are single-letter abbreviations for some that are heavily used in the test files.
bsr=[anycrlf|unicode] specify \R handling
/B bincode show binary code without lengths
callout_info show callout information
convert=<options> request foreign pattern conversion
convert_glob_escape=c set glob escape character
convert_glob_separator=c set glob separator character
convert_length set convert buffer length
debug same as info,fullbincode
framesize show matching frame size
fullbincode show binary code with lengths
/I info show info about compiled pattern
hex unquoted characters are hexadecimal
jit[=<number>] use JIT
jitfast use JIT fast path
jitverify verify JIT use
locale=<name> use this locale
max_pattern_length=<n> set the maximum pattern length
memory show memory used
newline=<type> set newline type
null_context compile with a NULL context
parens_nest_limit=<n> set maximum parentheses depth
posix use the POSIX API
posix_nosub use the POSIX API with REG_NOSUB
push push compiled pattern onto the stack
pushcopy push a copy onto the stack
stackguard=<number> test the stackguard feature
subject_literal treat all subject lines as literal
tables=[0|1|2] select internal tables
use_length do not zero-terminate the pattern
utf8_input treat input as UTF-8
The effects of these modifiers are described in the following sections.
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 can be
specified when PCRE2 is built; if it is not, the default is set to Unicode.
The newline modifier specifies which characters are to be interpreted as newlines, both in the pattern
and in subject lines. The type must be one of CR, LF, CRLF, ANYCRLF, ANY, or NUL (in upper or lower
case).
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 different internal link sizes and different code unit widths. By using bincode, the same regression
tests can be used in different environments.
The fullbincode modifier, by contrast, does include length and offset values. This is used in a few
special tests that run only for specific code unit widths and link sizes, 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. Here are
some typical examples:
re> /(?i)(^a|^b)/m,info
Capture group count = 1
Compile options: multiline
Overall options: caseless multiline
First code unit at start or follows newline
Subject length lower bound = 1
re> /(?i)abc/info
Capture group count = 0
Compile options: <none>
Overall options: caseless
First code unit = 'a' (caseless)
Last code unit = 'c' (caseless)
Subject length lower bound = 3
"Compile options" are those specified by modifiers; "overall options" have added options that are taken
or deduced from the pattern. If both sets of options are the same, just a single "options" line is
output; if there are no options, the line is omitted. "First code unit" is where any match must start; if
there is more than one they are listed as "starting code units". "Last code unit" is the last literal
code unit that must be present in any match. This is not necessarily the last character. These lines are
omitted if no starting or ending code units are recorded. The subject length line is omitted when
no_start_optimize is set because the minimum length is not calculated when it can never be used.
The framesize modifier shows the size, in bytes, of the storage frames used by pcre2_match() for handling
backtracking. The size depends on the number of capturing parentheses in the pattern.
The callout_info modifier requests information about all the callouts in the pattern. A list of them is
output at the end of any other information that is requested. For each callout, either its number or
string is given, followed by the item that follows it in the pattern.
Passing a NULL context
Normally, pcre2test passes a context block to pcre2_compile(). If the null_context modifier is set,
however, NULL is passed. This is for testing that pcre2_compile() behaves correctly in this case (it uses
default values).
Specifying pattern characters in hexadecimal
The hex modifier specifies that the characters of the pattern, except for substrings enclosed in single
or double quotes, are to be interpreted as pairs of hexadecimal digits. This feature is provided as a way
of creating patterns that contain binary zeros and other non-printing characters. White space is
permitted between pairs of digits. For example, this pattern contains three characters:
/ab 32 59/hex
Parts of such a pattern are taken literally if quoted. This pattern contains nine characters, only two of
which are specified in hexadecimal:
/ab "literal" 32/hex
Either single or double quotes may be used. There is no way of including the delimiter within a
substring. The hex and expand modifiers are mutually exclusive.
Specifying the pattern's length
By default, patterns are passed to the compiling functions as zero-terminated strings but can be passed
by length instead of being zero-terminated. The use_length modifier causes this to happen. Using a length
happens automatically (whether or not use_length is set) when hex is set, because patterns specified in
hexadecimal may contain binary zeros.
If hex or use_length is used with the POSIX wrapper API (see "Using the POSIX wrapper API" below), the
REG_PEND extension is used to pass the pattern's length.
Specifying wide characters in 16-bit and 32-bit modes
In 16-bit and 32-bit modes, all input is automatically treated as UTF-8 and translated to UTF-16 or
UTF-32 when the utf modifier is set. For testing the 16-bit and 32-bit libraries in non-UTF mode, the
utf8_input modifier can be used. It is mutually exclusive with utf. Input lines are interpreted as UTF-8
as a means of specifying wide characters. More details are given in "Input encoding" above.
Generating long repetitive patterns
Some tests use long patterns that are very repetitive. Instead of creating a very long input line for
such a pattern, you can use a special repetition feature, similar to the one described for subject lines
above. If the expand modifier is present on a pattern, parts of the pattern that have the form
\[<characters>]{<count>}
are expanded before the pattern is passed to pcre2_compile(). For example, \[AB]{6000} is expanded to
"ABAB..." 6000 times. This construction cannot be nested. An initial "\[" sequence is recognized only if
"]{" followed by decimal digits and "}" is found later in the pattern. If not, the characters remain in
the pattern unaltered. The expand and hex modifiers are mutually exclusive.
If part of an expanded pattern looks like an expansion, but is really part of the actual pattern,
unwanted expansion can be avoided by giving two values in the quantifier. For example, \[AB]{6000,6000}
is not recognized as an expansion item.
If the info modifier is set on an expanded pattern, the result of the expansion is included in the
information that is output.
JIT compilation
Just-in-time (JIT) compiling is a heavyweight optimization that can greatly speed up pattern matching.
See the pcre2jit documentation for details. JIT compiling happens, optionally, after a pattern has been
successfully compiled into an internal form. The JIT compiler converts this to optimized machine code. It
needs to know whether the match-time options PCRE2_PARTIAL_HARD and PCRE2_PARTIAL_SOFT are going to be
used, because different code is generated for the different cases. See the partial modifier in "Subject
Modifiers" below for details of how these options are specified for each match attempt.
JIT compilation is requested by the jit pattern modifier, which may optionally be followed by an equals
sign and a number in the range 0 to 7. The three bits that make up the number specify which of the three
JIT operating modes are to be compiled:
1 compile JIT code for non-partial matching
2 compile JIT code for soft partial matching
4 compile JIT code for hard partial matching
The possible values for the jit modifier are therefore:
0 disable JIT
1 normal matching only
2 soft partial matching only
3 normal and soft partial matching
4 hard partial matching only
6 soft and hard partial matching only
7 all three modes
If no number is given, 7 is assumed. The phrase "partial matching" means a call to pcre2_match() with
either the PCRE2_PARTIAL_SOFT or the PCRE2_PARTIAL_HARD option set. Note that such a call may return a
complete match; the options enable the possibility of a partial match, but do not require it. Note also
that if you request JIT compilation only for partial matching (for example, jit=2) but do not set the
partial modifier on a subject line, that match will not use JIT code because none was compiled for non-
partial matching.
If JIT compilation is successful, the compiled JIT code will automatically be used when an appropriate
type of match is run, except when incompatible run-time options are specified. For more details, see the
pcre2jit documentation. See also the jitstack modifier below for a way of setting the size of the JIT
stack.
If the jitfast modifier is specified, matching is done using the JIT "fast path" interface,
pcre2_jit_match(), which skips some of the sanity checks that are done by pcre2_match(), and of course
does not work when JIT is not supported. If jitfast is specified without jit, jit=7 is assumed.
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
compilation 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 in the match.
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_compile() 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
character tables are mutually exclusive.
Showing pattern memory
The memory modifier causes the size in bytes of the memory 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.
Here is an example:
re> /a(b)c/jit,memory
Memory allocation (code space): 21
Memory allocation (JIT code): 1910
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. The default for the library is set when PCRE2 is built, but
pcre2test sets its own default of 220, which is required for running the standard test suite.
Limiting the pattern length
The max_pattern_length modifier sets a limit, in code units, to the length of pattern that
pcre2_compile() will accept. Breaching the limit causes a compilation error. The default is the largest
number a PCRE2_SIZE variable can hold (essentially unlimited).
Using the POSIX wrapper API
The posix and posix_nosub modifiers cause pcre2test to call PCRE2 via the POSIX wrapper API rather than
its native API. When posix_nosub is used, the POSIX option REG_NOSUB is passed to regcomp(). The POSIX
wrapper supports only the 8-bit library. Note that it does not imply POSIX matching semantics; for more
detail see the pcre2posix documentation. The following pattern modifiers set options for the regcomp()
function:
caseless REG_ICASE
multiline REG_NEWLINE
dotall REG_DOTALL )
ungreedy REG_UNGREEDY ) These options are not part of
ucp REG_UCP ) the POSIX standard
utf REG_UTF8 )
The regerror_buffsize modifier specifies a size for the error buffer that is passed to regerror() in the
event of a compilation error. For example:
/abc/posix,regerror_buffsize=20
This provides a means of testing the behaviour of regerror() when the buffer is too small for the error
message. If this modifier has not been set, a large buffer is used.
The aftertext and allaftertext subject modifiers work as described below. All other modifiers are either
ignored, with a warning message, or cause an error.
The pattern is passed to regcomp() as a zero-terminated string by default, but if the use_length or hex
modifiers are set, the REG_PEND extension is used to pass it by length.
Testing the stack guard feature
The stackguard modifier is used to test the use of pcre2_set_compile_recursion_guard(), a function that
is provided to enable stack availability to be checked during compilation (see the pcre2api documentation
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 receives 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 value specified for the tables modifier must be one of the digits 0, 1, or 2. It causes a specific
set of built-in character tables to be passed to pcre2_compile(). This is used in the PCRE2 tests to
check behaviour with different 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 identified 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 under "Subject Modifiers" 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. These modifiers do not affect the compilation process.
aftertext show text after match
allaftertext show text after captures
allcaptures show all captures
allvector show the entire ovector
allusedtext show all consulted text
altglobal alternative global matching
/g global global matching
jitstack=<n> set size of JIT stack
mark show mark values
replace=<string> specify a replacement string
startchar show starting character when relevant
substitute_callout use substitution callouts
substitute_extended use PCRE2_SUBSTITUTE_EXTENDED
substitute_skip=<n> skip substitution number n
substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
substitute_stop=<n> skip substitution number n and greater
substitute_unknown_unset use PCRE2_SUBSTITUTE_UNKNOWN_UNSET
substitute_unset_empty use PCRE2_SUBSTITUTE_UNSET_EMPTY
These modifiers may not appear in a #pattern command. If you want them as defaults, set them in a
#subject command.
Specifying literal subject lines
If the subject_literal modifier is present on a pattern, all the subject lines that it matches are taken
as literal strings, with no interpretation of backslashes. It is not possible to set subject modifiers on
such lines, but any that are set as defaults by a #subject command are recognized.
Saving a compiled pattern
When a pattern with the push modifier is successfully compiled, it is pushed onto a stack of compiled
patterns, and pcre2test expects the next line to contain a new pattern (or a command) instead of a
subject line. This facility is used when saving compiled patterns to a file, as described in the section
entitled "Saving and restoring compiled patterns" below. If pushcopy is used instead of push, a copy of
the compiled pattern is stacked, leaving the original as current, ready to match the following input
lines. This provides a way of testing the pcre2_code_copy() function. The push and pushcopy modifiers
are incompatible with compilation modifiers such as global that act at match time. Any that are specified
are ignored (for the stacked copy), with a warning message, except for replace, which causes an error.
Note that jitverify, which is allowed, does not carry through to any subsequent matching that uses a
stacked pattern.
Testing foreign pattern conversion
The experimental foreign pattern conversion functions in PCRE2 can be tested by setting the convert
modifier. Its argument is a colon-separated list of options, which set the equivalent option for the
pcre2_pattern_convert() function:
glob PCRE2_CONVERT_GLOB
glob_no_starstar PCRE2_CONVERT_GLOB_NO_STARSTAR
glob_no_wild_separator PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR
posix_basic PCRE2_CONVERT_POSIX_BASIC
posix_extended PCRE2_CONVERT_POSIX_EXTENDED
unset Unset all options
The "unset" value is useful for turning off a default that has been set by a #pattern command. When one
of these options is set, the input pattern is passed to pcre2_pattern_convert(). If the conversion is
successful, the result is reflected in the output and then passed to pcre2_compile(). The normal utf and
no_utf_check options, if set, cause the PCRE2_CONVERT_UTF and PCRE2_CONVERT_NO_UTF_CHECK options to be
passed to pcre2_pattern_convert().
By default, the conversion function is allowed to allocate a buffer for its output. However, if the
convert_length modifier is set to a value greater than zero, pcre2test passes a buffer of the given
length. This makes it possible to test the length check.
The convert_glob_escape and convert_glob_separator modifiers can be used to specify the escape and
separator characters for glob processing, overriding the defaults, which are operating-system dependent.
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
endanchored set PCRE2_ENDANCHORED
dfa_restart set PCRE2_DFA_RESTART
dfa_shortest set PCRE2_DFA_SHORTEST
no_jit set PCRE2_NO_JIT
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 or posix_nosub 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(). The other modifiers
are ignored, with a warning message.
There is one additional modifier that can be used with the POSIX wrapper. It is ignored (with a warning)
if used for non-POSIX matching.
posix_startend=<n>[:<m>]
This causes the subject string to be passed to regexec() using the REG_STARTEND option, which uses
offsets to specify which part of the string is searched. If only one number is given, the end offset is
passed as the end of the subject string. For more detail of REG_STARTEND, see the pcre2posix
documentation. If the subject string contains binary zeros (coded as escapes such as \x{00} because
pcre2test does not support actual binary zeros in its input), you must use posix_startend to specify its
length.
Setting match controls
The following modifiers affect the matching process or request additional 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
allvector show the entire ovector
allusedtext show all consulted text (non-JIT only)
altglobal alternative global matching
callout_capture show captures at callout time
callout_data=<n> set a value to pass via callouts
callout_error=<n>[:<m>] control callout error
callout_extra show extra callout information
callout_fail=<n>[:<m>] control callout failure
callout_no_where do not show position of a callout
callout_none do not supply a callout function
copy=<number or name> copy captured substring
depth_limit=<n> set a depth limit
dfa use pcre2_dfa_match()
find_limits find match and depth limits
get=<number or name> extract captured substring
getall extract all captured substrings
/g global global matching
heap_limit=<n> set a limit on heap memory (Kbytes)
jitstack=<n> set size of JIT stack
mark show mark values
match_limit=<n> set a match limit
memory show heap memory usage
null_context match with a NULL context
offset=<n> set starting offset
offset_limit=<n> set offset limit
ovector=<n> set size of output vector
recursion_limit=<n> obsolete synonym for depth_limit
replace=<string> specify a replacement string
startchar show startchar when relevant
startoffset=<n> same as offset=<n>
substitute_callout use substitution callouts
substitute_extedded use PCRE2_SUBSTITUTE_EXTENDED
substitute_skip=<n> skip substitution number n
substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
substitute_stop=<n> skip substitution number n and greater
substitute_unknown_unset use PCRE2_SUBSTITUTE_UNKNOWN_UNSET
substitute_unset_empty use PCRE2_SUBSTITUTE_UNSET_EMPTY
zero_terminate pass the subject as zero-terminated
The effects of these modifiers are described in the following sections. When matching via the POSIX
wrapper API, the aftertext, allaftertext, and ovector subject modifiers work as described below. All
other modifiers are either ignored, with a warning message, or cause an error.
Showing more text
The aftertext modifier requests that as well as outputting the part of the subject 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 capture number.
The allusedtext modifier requests that all the text that was consulted during a successful pattern match
by the interpreter should be shown, for both full and partial matches. 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, for a complete match, 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 indicated in the output by '<' or '>' characters underneath them. Here is an
example:
re> /(?<=pqr)abc(?=xyz)/
data> 123pqrabcxyz456\=allusedtext
0: pqrabcxyz
<<< >>>
data> 123pqrabcxy\=ph,allusedtext
Partial match: pqrabcxy
<<<
The first, complete match shows that the matched string is "abc", with the preceding and following
strings "pqr" and "xyz" having been consulted during the match (when processing the assertions). The
partial match can indicate only the preceding string.
The startchar modifier requests that the starting character for the match be indicated, if it is
different to the start of the matched string. The only time when this occurs is when \K has been
processed as part of the match. In this situation, the output for the matched string is displayed from
the starting character instead of from the match point, with circumflex characters under the earlier
characters. For example:
re> /abc\Kxyz/
data> abcxyz\=startchar
0: abcxyz
^^^
Unlike allusedtext, the startchar modifier can be used with JIT. However, these two modifiers are
mutually exclusive.
Showing the value of all capture groups
The allcaptures modifier requests that the values of all potential captured 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
"<unset>". This modifier is not relevant for DFA matching (which does no capturing) and does not apply
when replace is specified; it is ignored, with a warning message, if present.
Showing the entire ovector, for all outcomes
The allvector modifier requests that the entire ovector be shown, whatever the outcome of the match.
Compare allcaptures, which shows only up to the maximum number of capture groups for the pattern, and
then only for a successful complete non-DFA match. This modifier, which acts after any match result, and
also for DFA matching, provides a means of checking that there are no unexpected modifications to ovector
fields. Before each match attempt, the ovector is filled with a special value, and if this is found in
both elements of a capturing pair, "<unchanged>" is output. After a successful match, this applies to all
groups after the maximum capture group for the pattern. In other cases it applies to the entire ovector.
After a partial match, the first two elements are the only ones that should be set. After a DFA match,
the amount of ovector that is used depends on the number of matches that were found.
Testing pattern callouts
A callout function is supplied when pcre2test calls the library matching functions, unless callout_none
is specified. Its behaviour can be controlled by various modifiers listed above whose names begin with
callout_. Details are given in the section entitled "Callouts" below. Testing callouts from
pcre2_substitute() is decribed separately in "Testing the substitution function" below.
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 subject. This makes a difference to the
matching process if the pattern begins with a lookbehind 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 characters occurs.
Testing substring extraction functions
The copy and get modifiers can be used to test the pcre2_substring_copy_xxx() and
pcre2_substring_get_xxx() functions. They can be given more than once, and each can specify a capture
group name or number, for example:
abcd\=copy=1,copy=3,get=G1
If the #subject command is used to set default copy and/or get lists, these can be unset by specifying a
negative number to cancel all numbered groups and an empty name to cancel all 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, followed by the name when the extraction was by name.
Testing the substitution function
If the replace modifier is set, the pcre2_substitute() function is called instead of one of the matching
functions. Note that replacement strings cannot contain commas, because a comma signifies the end of a
modifier. This is not thought to be an issue in a test program.
Unlike subject strings, pcre2test does not process replacement strings for escape sequences. In UTF mode,
a replacement string is checked to see if it is a valid UTF-8 string. If so, it is correctly converted to
a UTF string of the appropriate code unit width. If it is not a valid UTF-8 string, the individual code
units are copied directly. This provides a means of passing an invalid UTF-8 string for testing purposes.
The following modifiers set options (in additional to the normal match options) for pcre2_substitute():
global PCRE2_SUBSTITUTE_GLOBAL
substitute_extended PCRE2_SUBSTITUTE_EXTENDED
substitute_overflow_length PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
substitute_unknown_unset PCRE2_SUBSTITUTE_UNKNOWN_UNSET
substitute_unset_empty PCRE2_SUBSTITUTE_UNSET_EMPTY
After a successful substitution, the modified string is output, preceded by the number of replacements.
This may be zero if there were no matches. Here is a simple example of a substitution test:
/abc/replace=xxx
=abc=abc=
1: =xxx=abc=
=abc=abc=\=global
2: =xxx=xxx=
Subject and replacement strings should be kept relatively short (fewer than 256 characters) for
substitution tests, as fixed-size buffers are used. To make it easy to test for buffer overflow, if the
replacement string starts with a number in square brackets, that number is passed to pcre2_substitute()
as the size of the output buffer, with the replacement string starting at the next character. Here is an
example that tests the edge case:
/abc/
123abc123\=replace=[10]XYZ
1: 123XYZ123
123abc123\=replace=[9]XYZ
Failed: error -47: no more memory
The default action of pcre2_substitute() is to return PCRE2_ERROR_NOMEMORY when the output buffer is too
small. However, if the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set (by using the
substitute_overflow_length modifier), pcre2_substitute() continues to go through the motions of matching
and substituting (but not doing any callouts), in order to compute the size of buffer that is required.
When this happens, pcre2test shows the required buffer length (which includes space for the trailing
zero) as part of the error message. For example:
/abc/substitute_overflow_length
123abc123\=replace=[9]XYZ
Failed: error -47: no more memory: 10 code units are needed
A replacement string is ignored with POSIX and DFA matching. Specifying partial matching provokes an
error return ("bad option value") from pcre2_substitute().
Testing substitute callouts
If the substitute_callout modifier is set, a substitution callout function is set up. The null_context
modifier must not be set, because the address of the callout function is passed in a match context. When
the callout function is called (after each substitution), details of the the input and output strings are
output. For example:
/abc/g,replace=<$0>,substitute_callout
abcdefabcpqr
1(1) Old 0 3 "abc" New 0 5 "<abc>"
2(1) Old 6 9 "abc" New 8 13 "<abc>"
2: <abc>def<abc>pqr
The first number on each callout line is the count of matches. The parenthesized number is the number of
pairs that are set in the ovector (that is, one more than the number of capturing groups that were set).
Then are listed the offsets of the old substring, its contents, and the same for the replacement.
By default, the substitution callout function returns zero, which accepts the replacement and causes
matching to continue if /g was used. Two further modifiers can be used to test other return values. If
substitute_skip is set to a value greater than zero the callout function returns +1 for the match of that
number, and similarly substitute_stop returns -1. These cause the replacement to be rejected, and -1
causes no further matching to take place. If either of them are set, substitute_callout is assumed. For
example:
/abc/g,replace=<$0>,substitute_skip=1
abcdefabcpqr
1(1) Old 0 3 "abc" New 0 5 "<abc> SKIPPED"
2(1) Old 6 9 "abc" New 6 11 "<abc>"
2: abcdef<abc>pqr
abcdefabcpqr\=substitute_stop=1
1(1) Old 0 3 "abc" New 0 5 "<abc> STOPPED"
1: abcdefabcpqr
If both are set for the same number, stop takes precedence. Only a single skip or stop is supported,
which is sufficient for testing that the feature works.
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. The value is a number of
kibibytes (units of 1024 bytes). Setting zero reverts to the default of 32KiB. Providing a stack that is
larger than the default is necessary only for very complicated patterns. If jitstack is set non-zero on a
subject line it overrides any value that was set on the pattern.
Setting heap, match, and depth limits
The heap_limit, match_limit, and depth_limit modifiers set the appropriate limits 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 on a subject line, pcre2test calls the relevant matching function
several times, setting different values in the match context via pcre2_set_heap_limit(),
pcre2_set_match_limit(), or pcre2_set_depth_limit() until it finds the minimum values for each parameter
that allows the match to complete without error. If JIT is being used, only the match limit is relevant.
When using this modifier, the pattern should not contain any limit settings such as (*LIMIT_MATCH=...)
within it. If such a setting is present and is lower than the minimum matching value, the minimum value
cannot be found because pcre2_set_match_limit() etc. are only able to reduce the value of an in-pattern
limit; they cannot increase it.
For non-DFA matching, the minimum depth_limit number is a measure of how much nested backtracking happens
(that is, how deeply the pattern's tree is searched). In the case of DFA matching, depth_limit controls
the depth of recursive calls of the internal function that is used for handling pattern recursion,
lookaround assertions, and atomic groups.
For non-DFA matching, 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. In the case of DFA matching, match_limit controls the total number
of calls, both recursive and non-recursive, to the internal matching function, thus controlling the
overall amount of computing resource that is used.
For both kinds of matching, the heap_limit number, which is in kibibytes (units of 1024 bytes), limits
the amount of heap memory used for matching. A value of zero disables the use of any heap memory; many
simple pattern matches can be done without using the heap, so zero is not an unreasonable setting.
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 the sizes of all heap memory allocation and freeing calls
that occur during a call to pcre2_match() or pcre2_dfa_match(). These occur only when a match requires a
bigger vector than the default for remembering backtracking points (pcre2_match()) or for internal
workspace (pcre2_dfa_match()). In many cases there will be no heap memory used and therefore no
additional output. No heap memory is allocated during matching with JIT, so in that case the memory
modifier never has any effect. For this modifier to work, the null_context modifier must not be set on
both the pattern and the subject, though it can be set on one or the other.
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 an offset limit
The offset_limit modifier sets a limit for unanchored matches. If a match cannot be found starting at or
before this offset in the subject, a "no match" return is given. The data value is a number of code
units, not characters. When this modifier is used, the use_offset_limit modifier must have been set for
the pattern; if not, an error is generated.
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.
A value of zero is useful when testing the POSIX API because it causes regexec() to be called with a NULL
capture vector. When not testing the POSIX API, a value of zero is used to cause
pcre2_match_data_create_from_pattern() to be called, in order to create a match block of exactly the
right size for the pattern. (It is not possible to create a match block with a zero-length ovector; there
is always at least one pair of offsets.)
Passing the subject as zero-terminated
By default, the subject string is passed to a native API matching function with its correct length. In
order to test the facility for passing a zero-terminated string, the zero_terminate modifier is provided.
It causes the length to be passed as PCRE2_ZERO_TERMINATED. When matching via the POSIX interface, this
modifier is ignored, with a warning.
When testing pcre2_substitute(), this modifier also has the effect of passing the replacement string as
zero-terminated.
Passing a NULL context
Normally, pcre2test passes a context block to pcre2_match(), pcre2_dfa_match(), pcre2_jit_match() or
pcre2_substitute(). If the null_context modifier is set, however, NULL is passed. This is for testing
that the matching and substitution functions behave correctly in this case (they use default values).
This modifier cannot be used with the find_limits or substitute_callout modifiers.
THE ALTERNATIVE MATCHING FUNCTION
By default, pcre2test uses the standard PCRE2 matching function, pcre2_match() to match each subject
line. PCRE2 also supports an alternative matching function, pcre2_dfa_match(), which operates in a
different 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 subject. 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 substrings, 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 code unit offset of the start of the failing character is
also output. Here is an example of an interactive pcre2test run.
$ pcre2test
PCRE2 version 10.22 2016-07-29
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 shown by pcre2test unless the
allcaptures modifier is specified. 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 "<unset>", as for the second data line.
re> /(a)|(b)/
data> a
0: a
1: a
data> b
0: b
1: <unset>
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
definition 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 the offset modifier 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
assertion, \b, or \B was involved. (\K is not supported for DFA matching.)
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_PARTIAL 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\=ps,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 function is called during matching
unless callout_none is specified. This works with both matching functions, and with JIT, though there are
some differences in behaviour. The output for callouts with numerical arguments and those with string
arguments is slightly different.
Callouts with numerical arguments
By default, the callout function displays the callout number, the start and current positions in the
subject 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, or if the current
position precedes the start position, which can happen if the callout is in a lookbehind assertion.
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 whenever 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 "<unset>" is
output.
Callouts with string arguments
The output for a callout with a string argument is similar, except that instead of outputting a callout
number before the position indicators, the callout string and its offset in the pattern string are output
before the reflection of the subject string, and the subject string is reflected for each callout. For
example:
re> /^ab(?C'first')cd(?C"second")ef/
data> abcdefg
Callout (7): 'first'
--->abcdefg
^ ^ c
Callout (20): "second"
--->abcdefg
^ ^ e
0: abcdef
Callout modifiers
The callout function in pcre2test returns zero (carry on matching) by default, but you can use a
callout_fail modifier in a subject line to change this and other parameters of the callout (see below).
If the callout_capture modifier is set, the current captured groups are output when a callout occurs.
This is useful only for non-DFA matching, as pcre2_dfa_match() does not support capturing, so no captures
are ever shown.
The normal callout output, showing the callout number or pattern offset (as described above) is
suppressed if the callout_no_where modifier is set.
When using the interpretive matching function pcre2_match() without JIT, setting the callout_extra
modifier causes additional output from pcre2test's callout function to be generated. For the first
callout in a match attempt at a new starting position in the subject, "New match attempt" is output. If
there has been a backtrack since the last callout (or start of matching if this is the first callout),
"Backtrack" is output, followed by "No other matching paths" if the backtrack ended the previous match
attempt. For example:
re> /(a+)b/auto_callout,no_start_optimize,no_auto_possess
data> aac\=callout_extra
New match attempt
--->aac
+0 ^ (
+1 ^ a+
+3 ^ ^ )
+4 ^ ^ b
Backtrack
--->aac
+3 ^^ )
+4 ^^ b
Backtrack
No other matching paths
New match attempt
--->aac
+0 ^ (
+1 ^ a+
+3 ^^ )
+4 ^^ b
Backtrack
No other matching paths
New match attempt
--->aac
+0 ^ (
+1 ^ a+
Backtrack
No other matching paths
New match attempt
--->aac
+0 ^ (
+1 ^ a+
No match
Notice that various optimizations must be turned off if you want all possible matching paths to be
scanned. If no_start_optimize is not used, there is an immediate "no match", without any callouts,
because the starting optimization fails to find "b" in the subject, which it knows must be present for
any match. If no_auto_possess is not used, the "a+" item is turned into "a++", which reduces the number
of backtracks.
The callout_extra modifier has no effect if used with the DFA matching function, or with JIT.
Return values from callouts
The default return from the callout function is zero, which allows matching to continue. The callout_fail
modifier can be given one or two numbers. If there is only one number, 1 is returned instead of 0
(causing matching to backtrack) when a callout of that number is reached. If two numbers (<n>:<m>) are
given, 1 is returned when callout <n> is reached and there have been at least <m> callouts. The
callout_error modifier is similar, except that PCRE2_ERROR_CALLOUT is returned, causing the entire
matching process to be aborted. If both these modifiers are set for the same callout number,
callout_error takes precedence. Note that callouts with string arguments are always given the number
zero.
The callout_data modifier can be given an unsigned or a negative number. This is set as the "user data"
that is passed to the matching function, and passed back when the callout function is invoked. Any value
other than zero is used as a return from pcre2test's callout function.
Inserting callouts can be helpful when using pcre2test to check complicated 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.
SAVING AND RESTORING COMPILED PATTERNS
It is possible to save compiled patterns on disc or elsewhere, and reload them later, subject to a number
of restrictions. JIT data cannot be saved. The host on which the patterns are reloaded must be running
the same version of PCRE2, with the same code unit width, and must also have the same endianness, pointer
width and PCRE2_SIZE type. Before compiled patterns can be saved they must be serialized, that is,
converted to a stream of bytes. A single byte stream may contain any number of compiled patterns, but
they must all use the same character tables. A single copy of the tables is included in the byte stream
(its size is 1088 bytes).
The functions whose names begin with pcre2_serialize_ are used for serializing and de-serializing. They
are described in the pcre2serialize documentation. In this section we describe the features of pcre2test
that can be used to test these functions.
Note that "serialization" in PCRE2 does not convert compiled patterns to an abstract format like Java or
.NET. It just makes a reloadable byte code stream. Hence the restrictions on reloading mentioned above.
In pcre2test, when a pattern with push modifier is successfully compiled, it is pushed onto a stack of
compiled patterns, and pcre2test expects the next line to contain a new pattern (or command) instead of a
subject line. By contrast, the pushcopy modifier causes a copy of the compiled pattern to be stacked,
leaving the original available for immediate matching. By using push and/or pushcopy, a number of
patterns can be compiled and retained. These modifiers are incompatible with posix, and control modifiers
that act at match time are ignored (with a message) for the stacked patterns. The jitverify modifier
applies only at compile time.
The command
#save <filename>
causes all the stacked patterns to be serialized and the result written to the named file. Afterwards,
all the stacked patterns are freed. The command
#load <filename>
reads the data in the file, and then arranges for it to be de-serialized, with the resulting compiled
patterns added to the pattern stack. The pattern on the top of the stack can be retrieved by the #pop
command, which must be followed by lines of subjects that are to be matched with the pattern, terminated
as usual by an empty line or end of file. This command may be followed by a modifier list containing only
control modifiers that act after a pattern has been compiled. In particular, hex, posix, posix_nosub,
push, and pushcopy are not allowed, nor are any option-setting modifiers. The JIT modifiers are, however
permitted. Here is an example that saves and reloads two patterns.
/abc/push
/xyz/push
#save tempfile
#load tempfile
#pop info
xyz
#pop jit,bincode
abc
If jitverify is used with #pop, it does not automatically imply jit, which is different behaviour from
when it is used on a pattern.
The #popcopy command is analagous to the pushcopy modifier in that it makes current a copy of the topmost
stack pattern, leaving the original still on the stack.
SEE ALSO
pcre2(3), pcre2api(3), pcre2callout(3), pcre2jit, pcre2matching(3), pcre2partial(d), pcre2pattern(3),
pcre2serialize(3).
AUTHOR
Philip Hazel
University Computing Service
Cambridge, England.
REVISION
Last updated: 30 July 2019
Copyright (c) 1997-2019 University of Cambridge.