walkero
/
pcre2
1
0
Fork 0
Code Issues Pull Requests Projects Releases 1 Wiki Activity
pcre2/doc/pcre2test.txt

1074 lines
48 KiB
Plaintext
Raw Normal View History

Documentation scripts
2014-09-23 13:35:51 +02:00
PCRE2TEST(1) General Commands Manual PCRE2TEST(1)
NAME
pcre2test - a program for testing Perl-compatible regular expressions.
SYNOPSIS
pcre2test [options] [input file [output file]]
pcre2test is a test program for the PCRE2 regular expression libraries,
but it can also be used for experimenting with regular expressions.
This document describes the features of the test program; for details
of the regular expressions themselves, see the pcre2pattern documenta-
tion. For details of the PCRE2 library function calls and their
options, see the pcre2api documentation.
The input for pcre2test is a sequence of regular expression patterns
and subject strings to be matched. The output shows the result of each
match attempt. Modifiers on the command line, the patterns, and the
subject lines specify PCRE2 function options, control how the subject
is processed, and what output is produced.
As the original fairly simple PCRE library evolved, it acquired many
different features, and as a result, the original pcretest program
ended up with a lot of options in a messy, arcane syntax, for testing
all the features. The move to the new PCRE2 API provided an opportunity
to re-implement the test program as pcre2test, with a cleaner modifier
syntax. Nevertheless, there are still many obscure modifiers, some of
which are specifically designed for use in conjunction with the test
script and data files that are distributed as part of PCRE2. All the
modifiers are documented here, some without much justification, but
many of them are unlikely to be of use except when testing the
libraries.
PCRE2's 8-BIT, 16-BIT AND 32-BIT LIBRARIES
Different versions of the PCRE2 library can be built to support charac-
ter strings that are encoded in 8-bit, 16-bit, or 32-bit code units.
One, two, or all three of these libraries may be simultaneously
installed. The pcre2test program can be used to test all the libraries.
However, its own input and output are always in 8-bit format. When
testing the 16-bit or 32-bit libraries, patterns and subject strings
are converted to 16- or 32-bit format before being passed to the
library functions. Results are converted back to 8-bit code units for
output.
In the rest of this document, the names of library functions and struc-
tures are given in generic form, for example, pcre_compile(). The
actual names used in the libraries have a suffix _8, _16, or _32, as
appropriate.
INPUT ENCODING
Input to pcre2test is processed line by line, either by calling the C
library's fgets() function, or via the libreadline library (see below).
In Unix-like environments, fgets() treats any bytes other than newline
as data characters. However, in some Windows environments character 26
(hex 1A) causes an immediate end of file, and no further data is read.
For maximum portability, therefore, it is safest to avoid non-printing
characters in pcre2test input files.
COMMAND LINE OPTIONS
-8 If the 8-bit library has been built, this option causes it to
be used (this is the default). If the 8-bit library has not
been built, this option causes an error.
-16 If the 16-bit library has been built, this option causes it
to be used. If only the 16-bit library has been built, this
is the default. If the 16-bit library has not been built,
this option causes an error.
-32 If the 32-bit library has been built, this option causes it
to be used. If only the 32-bit library has been built, this
is the default. If the 32-bit library has not been built,
this option causes an error.
-b Behave as if each pattern has the /fullbincode modifier; the
full internal binary form of the pattern is output after com-
pilation.
-C Output the version number of the PCRE2 library, and all
available information about the optional features that are
included, and then exit with zero exit code. All other
options are ignored.
-C option Output information about a specific build-time option, then
exit. This functionality is intended for use in scripts such
as RunTest. The following options output the value and set
the exit code as indicated:
ebcdic-nl the code for LF (= NL) in an EBCDIC environment:
0x15 or 0x25
0 if used in an ASCII environment
exit code is always 0
linksize the configured internal link size (2, 3, or 4)
exit code is set to the link size
newline the default newline setting:
CR, LF, CRLF, ANYCRLF, or ANY
exit code is always 0
bsr the default setting for what \R matches:
ANYCRLF or ANY
exit code is always 0
The following options output 1 for true or 0 for false, and
set the exit code to the same value:
ebcdic compiled for an EBCDIC environment
jit just-in-time support is available
pcre16 the 16-bit library was built
pcre32 the 32-bit library was built
pcre8 the 8-bit library was built
unicode Unicode support is available
If an unknown option is given, an error message is output;
the exit code is 0.
-d Behave as if each pattern has the debug modifier; the inter-
nal form and information about the compiled pattern is output
after compilation; -d is equivalent to -b -i.
-dfa Behave as if each subject line has the dfa modifier; matching
is done using the pcre2_dfa_match() function instead of the
default pcre2_match().
-help Output a brief summary these options and then exit.
-i Behave as if each pattern has the /info modifier; information
about the compiled pattern is given after compilation.
-jit Behave as if each pattern line has the jit modifier; after
successful compilation, each pattern is passed to the just-
in-time compiler, if available.
-pattern modifier-list
Behave as if each pattern line contains the given modifiers.
-q Do not output the version number of pcre2test at the start of
execution.
-S size On Unix-like systems, set the size of the run-time stack to
size megabytes.
-subject modifier-list
Behave as if each subject line contains the given modifiers.
-t Run each compile and match many times with a timer, and out-
put the resulting times per compile or match. You can control
the number of iterations that are used for timing by follow-
ing -t with a number (as a separate item on the command
line). For example, "-t 1000" iterates 1000 times. The
default is to iterate 500,000 times.
-tm This is like -t except that it times only the matching phase,
not the compile phase.
-T -TM These behave like -t and -tm, but in addition, at the end of
a run, the total times for all compiles and matches are out-
put.
-version Output the PCRE2 version number and then exit.
DESCRIPTION
If pcre2test is given two filename arguments, it reads from the first
and writes to the second. If it is given only one filename argument, it
reads from that file and writes to stdout. Otherwise, it reads from
stdin and writes to stdout, and prompts for each line of input, using
"re>" to prompt for regular expression patterns, and "data>" to prompt
for subject lines.
When pcre2test is built, a configuration option can specify that it
should be linked with the libreadline or libedit library. When this is
done, if the input is from a terminal, it is read using the readline()
function. This provides line-editing and history facilities. The output
from the -help option states whether or not readline() will be used.
The program handles any number of tests, each of which consists of a
set of input lines. Each set starts with a regular expression pattern,
followed by any number of subject lines to be matched against that pat-
tern. In between sets of test data, command lines that begin with a
hash (#) character may appear. This file format, with some restric-
tions, can also be processed by the perltest.pl script that is distrib-
uted with PCRE2 as a means of checking that the behaviour of PCRE2 and
Perl is the same.
Each subject line is matched separately and independently. If you want
to do multi-line matches, you have to use the \n escape sequence (or \r
or \r\n, etc., depending on the newline setting) in a single line of
input to encode the newline sequences. There is no limit on the length
of subject lines; the input buffer is automatically extended if it is
too small. There is a replication feature that makes it possible to
generate long subject lines without having to supply them explicitly.
An empty line or the end of the file signals the end of the subject
lines for a test, at which point a new pattern or command line is
expected if there is still input to be read.
COMMAND LINES
In between sets of test data, a line that begins with a hash (#) char-
acter is interpreted as a command line. If the first character is fol-
lowed by white space or an exclamation mark, the line is treated as a
comment, and ignored. Otherwise, the following commands are recog-
nized:
#forbid_utf
Subsequent patterns automatically have the PCRE2_NEVER_UTF and
PCRE2_NEVER_UCP options set, which locks out the use of UTF and Unicode
property features. This is a trigger guard that is used in test files
to ensure that UTF/Unicode tests are not accidentally added to files
that are used when UTF support is not included in the library. This
effect can also be obtained by the use of #pattern; the difference is
that #forbid_utf cannot be unset, and the automatic options are not
displayed in pattern information, to avoid cluttering up test output.
#pattern <modifier-list>
This command sets a default modifier list that applies to all subse-
quent patterns. Modifiers on a pattern can change these settings.
#perltest
The appearance of this line causes all subsequent modifier settings to
be checked for compatibility with the perltest.pl script, which is used
to confirm that Perl gives the same results as PCRE2. Also, apart from
comment lines, none of the other command lines are permitted, because
they and many of the modifiers are specific to pcre2test, and should
not be used in test files that are also processed by perltest.pl. The
#perltest command helps detect tests that are accidentally put in the
wrong file.
#subject <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-
tings.
MODIFIER SYNTAX
Modifier lists are used with both pattern and subject lines. Items in a
list are separated by commas and optional white space. Some modifiers
may be given for both patterns and subject lines, whereas others are
valid for one or the other only. Each modifier has a long name, for
example "anchored", and some of them must be followed by an equals sign
and a value, for example, "offset=12". Modifiers that do not take val-
ues may be preceded by a minus sign to turn off a previous default set-
ting.
A few of the more common modifiers can also be specified as single let-
ters, for example "i" for "caseless". In documentation, following the
Perl convention, these are written with a slash ("the /i modifier") for
clarity. Abbreviated modifiers must all be concatenated in the first
item of a modifier list. If the first item is not recognized as a long
modifier name, it is interpreted as a sequence of these abbreviations.
For example:
/abc/ig,newline=cr,jit=3
This is a pattern line whose modifier list starts with two one-letter
modifiers (/i and /g). The lower-case abbreviated modifiers are the
same as used in Perl.
PATTERN SYNTAX
A pattern line must start with one of the following characters (common
symbols, excluding pattern meta-characters):
/ ! " ' ` - = _ : ; , % & @ ~
This is interpreted as the pattern's delimiter. A regular expression
may be continued over several input lines, in which case the newline
characters are included within it. It is possible to include the delim-
iter within the pattern by escaping it with a backslash, for example
/abc\/def/
If you do this, the escape and the delimiter form part of the pattern,
but since the delimiters are all non-alphanumeric, this does not affect
its interpretation. If the terminating delimiter is immediately fol-
lowed by a backslash, for example,
/abc/\
then a backslash is added to the end of the pattern. This is done to
provide a way of testing the error condition that arises if a pattern
finishes with a backslash, because
/abc\/
is interpreted as the first line of a pattern that starts with "abc/",
causing pcre2test to read the next line as a continuation of the regu-
lar expression.
A pattern can be followed by a modifier list (details below).
SUBJECT LINE SYNTAX
Before each subject line is passed to pcre2_match() or
pcre2_dfa_match(), leading and trailing white space is removed, and the
line is scanned for backslash escapes. The following provide a means of
encoding non-printing characters in a visible way:
\a alarm (BEL, \x07)
\b backspace (\x08)
\e escape (\x27)
\f form feed (\x0c)
\n newline (\x0a)
\r carriage return (\x0d)
\t tab (\x09)
\v vertical tab (\x0b)
\nnn octal character (up to 3 octal digits); always
a byte unless > 255 in UTF-8 or 16-bit or 32-bit mode
\o{dd...} octal character (any number of octal digits}
\xhh hexadecimal byte (up to 2 hex digits)
\x{hh...} hexadecimal character (any number of hex digits)
The use of \x{hh...} is not dependent on the use of the utf modifier on
the pattern. It is recognized always. There may be any number of hexa-
decimal digits inside the braces; invalid values provoke error mes-
sages.
Note that \xhh specifies one byte rather than one character in UTF-8
mode; this makes it possible to construct invalid UTF-8 sequences for
testing purposes. On the other hand, \x{hh} is interpreted as a UTF-8
character in UTF-8 mode, generating more than one byte if the value is
greater than 127. When testing the 8-bit library not in UTF-8 mode,
\x{hh} generates one byte for values less than 256, and causes an error
for greater values.
In UTF-16 mode, all 4-digit \x{hhhh} values are accepted. This makes it
possible to construct invalid UTF-16 sequences for testing purposes.
In UTF-32 mode, all 4- to 8-digit \x{...} values are accepted. This
makes it possible to construct invalid UTF-32 sequences for testing
purposes.
There is a special backslash sequence that specifies replication of one
or more characters:
\[<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 marke the end of the subject
string and the start of a modifier list. For example:
abc\=notbol,notempty
A backslash followed by any other non-alphanumeric character just
escapes that character. A backslash followed by anything else causes an
error. However, if the very last character in the line is a backslash
(and there is no modifier list), it is ignored. This gives a way of
passing an empty line as data, since a real empty line terminates the
data input.
PATTERN MODIFIERS
There are three types of modifier that can appear in pattern lines, two
of which may also be used in a #pattern command. A pattern's modifier
list can add to or override default modifiers that were set by a previ-
ous #pattern command.
Setting compilation options
The following modifiers set options for pcre2_compile(). The most com-
mon ones have single-letter abbreviations. See pcreapi for a descrip-
tion of their effects.
allow_empty_class set PCRE2_ALLOW_EMPTY_CLASS
alt_bsux set PCRE2_ALT_BSUX
anchored set PCRE2_ANCHORED
auto_callout set PCRE2_AUTO_CALLOUT
/i caseless set PCRE2_CASELESS
dollar_endonly set PCRE2_DOLLAR_ENDONLY
/s dotall set PCRE2_DOTALL
dupnames set PCRE2_DUPNAMES
/x extended set PCRE2_EXTENDED
firstline set PCRE2_FIRSTLINE
match_unset_backref set PCRE2_MATCH_UNSET_BACKREF
/m multiline set PCRE2_MULTILINE
never_ucp set PCRE2_NEVER_UCP
never_utf set PCRE2_NEVER_UTF
no_auto_capture set PCRE2_NO_AUTO_CAPTURE
no_auto_possess set PCRE2_NO_AUTO_POSSESS
no_start_optimize set PCRE2_NO_START_OPTIMIZE
no_utf_check set PCRE2_NO_UTF_CHECK
ucp set PCRE2_UCP
ungreedy set PCRE2_UNGREEDY
utf set PCRE2_UTF
As well as turning on the PCRE2_UTF option, the utf modifier causes all
non-printing characters in output strings to be printed using the
\x{hh...} notation. Otherwise, those less than 0x100 are output in hex
without the curly brackets.
Setting compilation controls
The following modifiers affect the compilation process or request
information about the pattern:
bsr=[anycrlf|unicode] specify \R handling
/B bincode show binary code without lengths
debug same as info,fullbincode
fullbincode show binary code with lengths
/I info show info about compiled pattern
hex pattern is coded in hexadecimal
jit[=<number>] use JIT
locale=<name> use this locale
memory show memory used
newline=<type> set newline type
parens_nest_limit=<n> set maximum parentheses depth
perlcompat lock out non-Perl modifiers
posix use the POSIX API
stackguard=<number> test the stackguard feature
tables=[0|1|2] select internal tables
use_length use the pattern's length
The effects of these modifiers are described in the following sections.
FIXME: Give more examples.
Newline and \R handling
The bsr modifier specifies what \R in a pattern should match. If it is
set to "anycrlf", \R matches CR, LF, or CRLF only. If it is set to
"unicode", \R matches any Unicode newline sequence. The default is
specified when PCRE2 is built, with the default default being Unicode.
The newline modifier specifies which characters are to be interpreted
as newlines, both in the pattern and (by default) in subject lines. The
type must be one of CR, LF, CRLF, ANYCRLF, or ANY.
Both the \R and newline settings can be changed at match time, but if
this is done, JIT matching is disabled.
Information about a pattern
The debug modifier is a shorthand for info,fullbincode, requesting all
available information.
The bincode modifier causes a representation of the compiled code to be
output after compilation. This information does not contain length and
offset values, which ensures that the same output is generated for dif-
ferent internal link sizes and different code unit widths. By using
bincode, the same regression tests can be used in different environ-
ments.
The fullbincode modifier, by contrast, does include length and offset
values. This is used in a few special tests and is also useful for one-
off tests.
The info modifier requests information about the compiled pattern
(whether it is anchored, has a fixed first character, and so on). The
information is obtained from the pcre2_pattern_info() function.
Specifying a pattern in hex
The hex modifier specifies that the characters of the pattern are to be
interpreted as pairs of hexadecimal digits. White space is permitted
between pairs. For example:
/ab 32 59/hex
This feature is provided as a way of creating patterns that contain
binary zero characters. When hex is set, it implies use_length.
Using the pattern's length
By default, pcre2test passes patterns as zero-terminated strings to
pcre2_compile(), giving the length as -1. If use_length is set, the
length of the pattern is passed. This is implied if hex is set.
JIT compilation
The /jit modifier may optionally be followed by a number in the range 0
to 7:
0 disable JIT
1 normal match only
2 soft partial match only
3 normal match and soft partial match
4 hard partial match only
6 soft and hard partial match
7 all three modes
If no number is given, 7 is assumed. If JIT compilation is successful,
the compiled JIT code will automatically be used when pcre2_match() is
run, 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 jitverify modifier is specified, the text "(JIT)" is added to
the first output line after a match or non match when JIT-compiled code
was actually used. This modifier can also be set on a subject line.
Setting a locale
The /locale modifier must specify the name of a locale, for example:
/pattern/locale=fr_FR
The given locale is set, pcre2_maketables() is called to build a set of
character tables for the locale, and this is then passed to pcre2_com-
pile() when compiling the regular expression. The same tables are used
when matching the following subject lines. The /locale modifier applies
only to the pattern on which it appears, but can be given in a #pattern
command if a default is needed. Setting a locale and alternate charac-
ter tables are mutually exclusive.
Showing pattern memory
The /memory modifier causes the size in bytes of the memory block used
to hold the compiled pattern to be output. This does not include the
size of the pcre2_code block; it is just the actual compiled data. If
the pattern is subsequently passed to the JIT compiler, the size of the
JIT compiled code is also output.
Limiting nested parentheses
The parens_nest_limit modifier sets a limit on the depth of nested
parentheses in a pattern. Breaching the limit causes a compilation
error.
Using the POSIX wrapper API
The /posix modifier causes pcre2test to call PCRE2 via the POSIX wrap-
per API rather than its native API. This supports only the 8-bit
library. When the POSIX API is being used, the following pattern modi-
fiers set options for the regcomp() function:
caseless REG_ICASE
multiline REG_NEWLINE
no_auto_capture REG_NOSUB
dotall REG_DOTALL )
ungreedy REG_UNGREEDY ) These options are not part of
ucp REG_UCP ) the POSIX standard
utf REG_UTF8 )
The aftertext and allaftertext subject modifiers work as described
below. All other modifiers cause an error.
Testing the stack guard feature
The /stackguard modifier is used to test the use of pcre2_set_com-
pile_recursion_guard(), a function that is provided to enable stack
availability to be checked during compilation (see the pcre2api docu-
mentation for details). If the number specified by the modifier is
greater than zero, pcre2_set_compile_recursion_guard() is called to set
up callback from pcre2_compile() to a local function. The argument it
is passed is the current nesting parenthesis depth; if this is greater
than the value given by the modifier, non-zero is returned, causing the
compilation to be aborted.
Using alternative character tables
The /tables modifier must be followed by a single digit. It causes a
specific set of built-in character tables to be passed to pcre2_com-
pile(). This is used in the PCRE2 tests to check behaviour with differ-
ent character tables. The digit specifies the tables as follows:
0 do not pass any special character tables
1 the default ASCII tables, as distributed in
pcre2_chartables.c.dist
2 a set of tables defining ISO 8859 characters
In table 2, some characters whose codes are greater than 128 are iden-
tified as letters, digits, spaces, etc. Setting alternate character
tables and a locale are mutually exclusive.
Setting certain match controls
The following modifiers are really subject modifiers, and are described
below. However, they may be included in a pattern's modifier list, in
which case they are applied to every subject line that is processed
with that pattern. They do not affect the compilation process.
aftertext show text after match
allaftertext show text after captures
allcaptures show all captures
allusedtext show all consulted text
/g global global matching
jitverify verify JIT usage
mark show mark values
These modifiers may not appear in a #pattern command. If you want them
as defaults, set them in a #subject command.
SUBJECT MODIFIERS
The modifiers that can appear in subject lines and the #subject command
are of two types.
Setting match options
The following modifiers set options for pcre2_match() or
pcre2_dfa_match(). See pcreapi for a description of their effects.
anchored set PCRE2_ANCHORED
dfa_restart set PCRE2_DFA_RESTART
dfa_shortest set PCRE2_DFA_SHORTEST
no_start_optimize set PCRE2_NO_START_OPTIMIZE
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
altglobal alternative global matching
bsr=[anycrlf|unicode] specify \R handling
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
jitverify verify JIT usage
mark show mark values
match_limit=>n> set a match limit
memory show memory usage
newline=<type> set newline type
offset=<n> set starting offset
ovector=<n> set size of output vector
recursion_limit=<n> set a recursion limit
The effects of these modifiers are described in the following sections.
FIXME: Give more examples.
Newline and \R handling
These modifiers set the newline and \R processing conventions for the
subject line, overriding any values that were set at compile time (as
described above). JIT matching is disabled if these settings are
changed at match time.
Showing more text
The aftertext modifier requests that as well as outputting the sub-
string that matched the entire pattern, pcre2test should in addition
output the remainder of the subject string. This is useful for tests
where the subject contains multiple copies of the same substring. The
allaftertext modifier requests the same action for captured substrings
as well as the main matched substring. In each case the remainder is
output on the following line with a plus character following the cap-
ture number.
The allusedtext modifier requests that all the text that was consulted
during a successful pattern match be shown. This 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 indicated in the output by
'<' or '>' characters underneath them. Here is an example:
/(?<=pqr)abc(?=xyz)/
123pqrabcxyz456\=allusedtext
0: pqrabcxyz
<<< >>>
This shows that the matched string is "abc", with the preceding and
following strings "pqr" and "xyz" also consulted during the match.
Showing the value of all capture groups
The allcaptures modifier requests that the values of all potential cap-
tured parentheses be output after a match. By default, only those up to
the highest one actually used in the match are output (corresponding to
the return code from pcre2_match()). Groups that did not take part in
the match are output as "<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.
The callout_data modifier can be given an unsigned or a negative num-
ber. Any value other than zero is used as a return from pcre2test's
callout function.
Testing substring extraction functions
The copy and get modifiers can be used to test the pcre2_sub-
string_copy_xxx() and pcre2_substring_get_xxx() functions. They can be
given more than once, and each can specify a group name or number, for
example:
abcd\=copy=1,copy=3,get=G1
If the #subject command is used to set default copy and get lists,
these can be unset by specifying a negative number for numbered groups
and an empty name for named groups.
The getall modifier tests pcre2_substring_list_get(), which extracts
all captured substrings.
If the subject line is successfully matched, the substrings extracted
by the convenience functions are output with C, G, or L after the
string number instead of a colon. This is in addition to the normal
full list. The string length (that is, the return from the extraction
function) is given in parentheses after each substring.
Finding all matches in a string
Searching for all possible matches within a subject can be requested by
the global or /altglobal modifier. After finding a match, the matching
function is called again to search the remainder of the subject. The
difference between global and altglobal is that the former uses the
start_offset argument to pcre2_match() or pcre2_dfa_match() to start
searching at a new point within the entire string (which is what Perl
does), whereas the latter passes over a shortened substring. This makes
a difference to the matching process if the pattern begins with a look-
behind assertion (including \b or \B).
If an empty string is matched, the next match is done with the
PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED flags set, in order to search
for another, non-empty, match at the same point in the subject. If this
match fails, the start offset is advanced, and the normal match is
retried. This imitates the way Perl handles such cases when using the
/g modifier or the split() function. Normally, the start offset is
advanced by one character, but if the newline convention recognizes
CRLF as a newline, and the current character is CR followed by LF, an
advance of two is used.
Setting the JIT stack size
The jitstack modifier provides a way of setting the maximum stack size
that is used by the just-in-time optimization code. It is ignored if
JIT optimization is not being used. Providing a stack that is larger
than the default 32K is necessary only for very complicated patterns.
Setting match and recursion limits
The match_limit and recursion_limit modifiers set the appropriate lim-
its in the match context. These values are ignored when the find_limits
modifier is specified.
Finding minimum limits
If the find_limits modifier is present, pcre2test calls pcre2_match()
several times, setting different values in the match context via
pcre2_set_match_limit() and pcre2_set_recursion_limit() until it finds
the minimum values for each parameter that allow pcre2_match() to com-
plete without error.
The match_limit number is a measure of the amount of backtracking that
takes place, and learning the minimum value can be instructive. For
most simple matches, the number is quite small, but for patterns with
very large numbers of matching possibilities, it can become large very
quickly with increasing length of subject string. The
match_limit_recursion number is a measure of how much stack (or, if
PCRE2 is compiled with NO_RECURSE, how much heap) memory is needed to
complete the match attempt.
Showing MARK names
The mark modifier causes the names from backtracking control verbs that
are returned from calls to pcre2_match() to be displayed. If a mark is
returned for a match, non-match, or partial match, pcre2test shows it.
For a match, it is on a line by itself, tagged with "MK:". Otherwise,
it is added to the non-match message.
Showing memory usage
The memory modifier causes pcre2test to log all memory allocation and
freeing calls that occur during a match operation.
Setting a starting offset
The offset modifier sets an offset in the subject string at which
matching starts. Its value is a number of code units, not characters.
Setting the size of the output vector
The ovector modifier applies only to the subject line in which it
appears, though of course it can also be used to set a default in a
#subject command. It specifies the number of pairs of offsets that are
available for storing matching information. The default is 15.
THE ALTERNATIVE MATCHING FUNCTION
By default, pcre2test uses the standard PCRE2 matching function,
pcre2_match() to match each subject line. PCRE2 also supports an alter-
native matching function, pcre2_dfa_match(), which operates in a dif-
ferent way, and has some restrictions. The differences between the two
functions are described in the pcre2matching documentation.
If the dfa modifier is set, the alternative matching function is used.
This function finds all possible matches at a given point in the sub-
ject. If, however, the dfa_shortest modifier is set, processing stops
after the first match is found. This is always the shortest possible
match.
DEFAULT OUTPUT FROM pcre2test
This section describes the output when the normal matching function,
pcre2_match(), is being used.
When a match succeeds, pcre2test outputs the list of captured sub-
strings, starting with number 0 for the string that matched the whole
pattern. Otherwise, it outputs "No match" when the return is
PCRE2_ERROR_NOMATCH, or "Partial match:" followed by the partially
matching substring when the return is PCRE2_ERROR_PARTIAL. (Note that
this is the entire substring that was inspected during the partial
match; it may include characters before the actual match start if a
lookbehind assertion, \K, \b, or \B was involved.)
For any other return, pcre2test outputs the PCRE2 negative error number
and a short descriptive phrase. If the error is a failed UTF string
check, the offset of the start of the failing character and the reason
code are also output. Here is an example of an interactive pcre2test
run.
$ pcre2test
PCRE2 version 9.00 2014-05-10
re> /^abc(\d+)/
data> abc123
0: abc123
1: 123
data> xyz
No match
Unset capturing substrings that are not followed by one that is set are
not returned by pcre2_match(), and are not shown by pcre2test. In the
following example, there are two capturing substrings, but when the
first data line is matched, the second, unset substring is not shown.
An "internal" unset substring is shown as "<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 \>4 is
past the end of the subject string):
re> /xyz/
data> xyz\=offset=4
Error -24 (bad offset value)
Note that whereas patterns can be continued over several lines (a plain
">" prompt is used for continuations), subject lines may not. However
newlines can be included in a subject by means of the \n escape (or \r,
\r\n, etc., depending on the newline sequence setting).
OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION
When the alternative matching function, pcre2_dfa_match(), is used, the
output consists of a list of all the matches that start at the first
point in the subject where there is at least one match. For example:
re> /(tang|tangerine|tan)/
data> yellow tangerine\=dfa
0: tangerine
1: tang
2: tan
(Using the normal matching function on this data finds only "tang".)
The longest matching string is always given first (and numbered zero).
After a PCRE2_ERROR_PARTIAL return, the output is "Partial match:",
followed by the partially matching substring. (Note that this is the
entire substring that was inspected during the partial match; it may
include characters before the actual match start if a lookbehind asser-
tion, \K, \b, or \B was involved.)
If global matching is requested, the search for further matches resumes
at the end of the longest match. For example:
re> /(tang|tangerine|tan)/g
data> yellow tangerine and tangy sultana\=dfa
0: tangerine
1: tang
2: tan
0: tang
1: tan
0: tan
The alternative matching function does not support substring capture,
so the modifiers that are concerned with captured substrings are not
relevant.
RESTARTING AFTER A PARTIAL MATCH
When the alternative matching function has given the PCRE2_ERROR_PAR-
TIAL return, indicating that the subject partially matched the pattern,
you can restart the match with additional subject data by means of the
dfa_restart modifier. For example:
re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
data> 23ja\=P,dfa
Partial match: 23ja
data> n05\=dfa,dfa_restart
0: n05
For further information about partial matching, see the pcre2partial
documentation.
CALLOUTS
If the pattern contains any callout requests, pcre2test's callout func-
tion is called during matching. This works with both matching func-
tions. By default, the called function displays the callout number, the
start and current positions in the text at the callout time, and the
next pattern item to be tested. For example:
--->pqrabcdef
0 ^ ^ \d
This output indicates that callout number 0 occurred for a match
attempt starting at the fourth character of the subject string, when
the pointer was at the seventh character, and when the next pattern
item was \d. Just one circumflex is output if the start and current
positions are the same.
Callouts numbered 255 are assumed to be automatic callouts, inserted as
a result of the /auto_callout pattern modifier. In this case, instead
of showing the callout number, the offset in the pattern, preceded by a
plus, is output. For example:
re> /\d?[A-E]\*/auto_callout
data> E*
--->E*
+0 ^ \d?
+3 ^ [A-E]
+8 ^^ \*
+10 ^ ^
0: E*
If a pattern contains (*MARK) items, an additional line is output when-
ever a change of latest mark is passed to the callout function. For
example:
re> /a(*MARK:X)bc/auto_callout
data> abc
--->abc
+0 ^ a
+1 ^^ (*MARK:X)
+10 ^^ b
Latest Mark: X
+11 ^ ^ c
+12 ^ ^
0: abc
The mark changes between matching "a" and "b", but stays the same for
the rest of the match, so nothing more is output. If, as a result of
backtracking, the mark reverts to being unset, the text "<unset>" is
output.
The callout function in pcre2test returns zero (carry on matching) by
default, but you can use a callout_fail modifier in a subject line (as
described above) to change this and other parameters of the callout.
Inserting callouts can be helpful when using pcre2test to check compli-
cated regular expressions. For further information about callouts, see
the pcre2callout documentation.
NON-PRINTING CHARACTERS
When pcre2test is outputting text in the compiled version of a pattern,
bytes other than 32-126 are always treated as non-printing characters
and are therefore shown as hex escapes.
When pcre2test is outputting text that is a matched part of a subject
string, it behaves in the same way, unless a different locale has been
set for the pattern (using the /locale modifier). In this case, the
isprint() function is used to distinguish printing and non-printing
characters.
SEE ALSO
pcre2(3), pcre16(3), pcre32(3), pcre2api(3), pcre2callout(3), pcre2jit,
pcre2matching(3), pcre2partial(d), pcre2pattern(3), pcre2precompile(3).
AUTHOR
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
REVISION
Last updated: 19 August 2014
Copyright (c) 1997-2014 University of Cambridge.