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PCRE2TEST(1) General Commands Manual PCRE2TEST(1)
pcre2test - a program for testing Perl-compatible regular expressions.
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. 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 func-
tion options, control how the subject is processed, and what output is
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
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
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
Input to pcre2test is processed line by line, either by calling the C
library's fgets() function, or via the libreadline library (see below).
The input is processed using using C's string functions, so must not
contain binary zeroes, even though in Unix-like environments, fgets()
treats any bytes other than newline as data characters. 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. There is a facility for specifying
a pattern's characters as hexadecimal pairs, thus making it possible to
include binary zeroes in a pattern for testing purposes. Subject lines
are processed for backslash escapes, which makes it possible to include
any data value.
-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-
-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:
exit code is always 0
bsr the default setting for what \R matches:
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 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
-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. 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 out-
-version Output the PCRE2 version number and then exit.
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 pat-
tern. 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 script that is distributed with PCRE2 as a means of
checking that the behaviour of PCRE2 and Perl is the same.
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.
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:
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 informa-
tion, 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 con-
tain 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 com-
piled 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, ANY-
CRLF, or ANY (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. Oth-
erwise, 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
modifier is used when #newline_default would set a default for the non-
#pattern <modifier-list>
This command sets a default modifier list that applies to all subse-
quent patterns. Modifiers on a pattern can change these settings.
The appearance of this line causes all subsequent modifier settings to
be checked for compatibility with the 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 The
#perltest command helps detect tests that are accidentally put in the
wrong file.
#pop [<modifiers>]
This command is used to manipulate the stack of compiled patterns, as
described in the section entitled "Saving and restoring compiled pat-
terns" 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 pat-
terns" below.
#subject <modifier-list>
This command sets a default modifier list that applies to all subse-
quent subject lines. Modifiers on a subject line can change these set-
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 charac-
ters, 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 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:
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.
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
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,
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
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).
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-
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
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:
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:
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
\= 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.
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(). The most com-
mon ones have single-letter abbreviations. See pcre2api for a descrip-
tion of their effects.
allow_empty_class set PCRE2_ALLOW_EMPTY_CLASS
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
/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_backslash_c set PCRE2_NEVER_BACKSLASH_C
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_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 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
callout_info show callout information
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[=<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
push push compiled pattern onto the stack
stackguard=<number> test the stackguard feature
tables=[0|1|2] select internal tables
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 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 in subject lines. The type must be
one of CR, LF, CRLF, ANYCRLF, or ANY (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 dif-
ferent internal link sizes and different code unit widths. By using
bincode, the same regression tests can be used in different environ-
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
Capturing subpattern 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
Capturing subpattern 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 callout_info modifier requests information about all the callouts
in the pattern. A list of them is output at the end of any other infor-
mation 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 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 and other non-printing characters. By default, pcre2test
passes patterns as zero-terminated strings to pcre2_compile(), giving
the length as PCRE2_ZERO_TERMINATED. However, for patterns specified in
hexadecimal, the actual length of the pattern is passed.
Generating long repetitive patterns
Some tests use long patterns that are very repetitive. Instead of cre-
ating 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
are expanded before the pattern is passed to pcre2_compile(). For exam-
ple, \[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.
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 rec-
ognized 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 com-
plete 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 automati-
cally 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 san-
ity 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 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 in the match.
Setting a locale
The /locale modifier must specify the name of a locale, for example:
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 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 modifier causes pcre2test to call PCRE2 via the POSIX wrap-
per API rather than its native API. This supports only the 8-bit
library. Note that it does not imply POSIX matching semantics; for
more detail see the pcre2posix documentation. When the POSIX API is
being used, the following pattern modifiers set options for the reg-
comp() 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 regerror_buffsize modifier specifies a size for the error buffer
that is passed to regerror() in the event of a compilation error. For
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 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
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 be-
haviour 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
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 may not appear in #pattern commands. These mod-
ifiers 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
replace=<string> specify a replacement string
startchar show starting character when relevant
substitute_extended use PCRE2_SUBSTITUTE_EXTENDED
substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
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.
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 pat-
terns" below. The push modifier is incompatible with compilation modi-
fiers such as global that act at match time. Any that are specified are
ignored, 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 this pattern.
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=<n> set a value to pass via callouts
callout_fail=<n>[:<m>] control callout failure
callout_none do not supply a callout function
copy=<number or name> copy captured substring
dfa use pcre2_dfa_match()
find_limits find match and recursion limits
get=<number or name> extract captured substring
getall extract all captured substrings
/g global global matching
jitstack=<n> set size of JIT stack
mark show mark values
match_limit=<n> set a match limit
memory show 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> set a recursion limit
replace=<string> specify a replacement string
startchar show startchar when relevant
startoffset=<n> same as offset=<n>
substitute_extedded use PCRE2_SUBSTITUTE_EXTENDED
substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
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.
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 sub-
strings as well as the main matched substring. In each case the remain-
der 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.
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:
re> /(?<=pqr)abc(?=xyz)/
data> 123pqrabcxyz456\=allusedtext
0: pqrabcxyz
<<< >>>
This 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 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
re> /abc\Kxyz/
data> abcxyz\=startchar
0: abcxyz
Unlike allusedtext, the startchar modifier can be used with JIT. How-
ever, these two modifiers are mutually exclusive.
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 "<unset>".
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
<n> is reached for the <m>th time. Note that callouts with string argu-
ments are always given the number zero. See "Callouts" below for a
description of the output when a callout it taken.
The callout_data modifier can be given an unsigned or a negative num-
ber. 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
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 lookbe-
hind 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_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
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 num-
bered 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 pro-
vides 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():
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, pre-
ceded by the number of replacements. This may be zero if there were no
matches. Here is a simple example of a substitution test:
1: =xxx=abc=
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:
1: 123XYZ123
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 sub-
stitute_overflow_length modifier), pcre2_substitute() continues to go
through the motions of matching and substituting, 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:
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
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 kilobytes.
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 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 modi-
fier 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_cre-
ate_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 func-
tion 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 has no effect, as there is no
facility for passing a length.)
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() or pcre2_jit_match(). If the null_context modifier is
set, however, NULL is passed. This is for testing that the matching
functions behave correctly in this case (they use default values). This
modifier cannot be used with the find_limits modifier or when testing
the substitution 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
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 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 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 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 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 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).
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, \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
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
If the pattern contains any callout requests, pcre2test's callout func-
tion is called during matching unless callout_none is specified. This
works with both matching functions.
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.
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:
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*
+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
re> /a(*MARK:X)bc/auto_callout
data> 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
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'
^ ^ c
Callout (20): "second"
^ ^ e
0: abcdef
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
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, con-
verted to a stream of bytes. A single byte stream may contain any num-
ber 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 pcre2serial-
ize documentation. In this section we describe the features of
pcre2test that can be used to test these functions.
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 this means, a number of patterns can be compiled and retained.
The push modifier is incompatible with posix, and control modifiers
that act at match time are ignored (with a message). The jitverify mod-
ifier 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
#load <filename>
reads the data in the file, and then arranges for it to be de-serial-
ized, with the resulting compiled patterns added to the pattern stack.
The pattern on the top of the stack can be retrieved by the #pop com-
mand, 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, and push 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.
#save tempfile
#load tempfile
#pop info
#pop jit,bincode
If jitverify is used with #pop, it does not automatically imply jit,
which is different behaviour from when it is used on a pattern.
pcre2(3), pcre2api(3), pcre2callout(3), pcre2jit, pcre2matching(3),
pcre2partial(d), pcre2pattern(3), pcre2serialize(3).
Philip Hazel
University Computing Service
Cambridge, England.
Last updated: 12 December 2015
Copyright (c) 1997-2015 University of Cambridge.