This section describes the set of utilities included with the Hyperscan library.

Quick Check: hscheck

The hscheck tool allows the user to quickly check whether Hyperscan supports a group of patterns. If a pattern is rejected by Hyperscan’s compiler, the compile error is provided on standard output.

For example, given the following three patterns (the last of which contains a syntax error) in a file called /tmp/test:


... the hscheck tool will produce the following output:

$ bin/hscheck -e /tmp/test

OK: 1:/foo.*bar/
OK: 2:/abc|def|ghi/
FAIL (compile): 3:/((foo|bar)/: Missing close parenthesis for group started at index 0.
SUMMARY: 1 of 3 failed.

Benchmarker: hsbench

The hsbench tool provides an easy way to measure Hyperscan’s performance for a particular set of patterns and corpus of data to be scanned.

Patterns are supplied in the format described below in Pattern Format, while the corpus must be provided in the form of a corpus database: this is a simple SQLite database format intended to allow for easy control of how a corpus is broken into blocks and streams.


A group of Python scripts for constructing corpora databases from various input types, such as PCAP network traffic captures or text files, can be found in the Hyperscan source tree in tools/hsbench/scripts.

Running hsbench

Given a file full of patterns specified with -e and a corpus database specified with -c, hsbench will perform a single-threaded benchmark and produce output like this:

$ hsbench -e /tmp/patterns -c /tmp/corpus.db

Signatures:        /tmp/patterns
Hyperscan info:    Version: 4.3.1 Features:  AVX2 Mode: STREAM
Expression count:  200
Bytecode size:     342,540 bytes
Database CRC:      0x6cd6b67c
Stream state size: 252 bytes
Scratch size:      18,406 bytes
Compile time:      0.153 seconds
Peak heap usage:   78,073,856 bytes

Time spent scanning:     0.600 seconds
Corpus size:             72,138,183 bytes (63,946 blocks in 8,891 streams)
Scan matches:            81 (0.001 matches/kilobyte)
Overall block rate:      2,132,004.45 blocks/sec
Overall throughput:      19,241.10 Mbit/sec

By default, the corpus is scanned twenty times, and the overall performance reported is computed based the total number of bytes scanned in the time it takes to perform all twenty scans. The number of repeats can be changed with the -n argument, and the results of each scan will be displayed if the --per-scan argument is specified.

To benchmark Hyperscan on more than one core, you can supply a list of cores with the -T argument, which will instruct hsbench to start one benchmark thread per core given and compute the throughput from the time taken to complete all of them.


For single-threaded benchmarks on multi-processor systems, we recommend using a utility like taskset to lock the hsbench process to one core and minimize jitter due to the operating system’s scheduler.

Correctness Testing: hscollider

The hscollider tool, or Pattern Collider, provides a way to verify Hyperscan’s matching behaviour. It does this by compiling and scanning patterns (either singly or in groups) against known corpora and comparing the results against another engine (the “ground truth”). Two sources of ground truth for comparison are available:

  • The PCRE library (
  • An NFA simulation run on Hyperscan’s compile-time graph representation. This is used if PCRE cannot support the pattern or if PCRE execution fails due to a resource limit.

Much of Hyperscan’s testing infrastructure is built on hscollider, and the tool is designed to take advantage of multiple cores and provide considerable flexibility in controlling the test. These options are described in the help (hscollider -h) and include:

  • Testing in streaming, block or vectored mode.
  • Testing corpora at different alignments in memory.
  • Testing patterns in groups of varying size.
  • Manipulating stream state or scratch space between tests.
  • Cross-compilation and serialization/deserialization of databases.
  • Synthetic generation of corpora given a pattern set.

Using hscollider to debug a pattern

One common use-case for hscollider is to determine whether Hyperscan will match a pattern in the expected location, and whether this accords with PCRE’s behaviour for the same case.

Here is an example. We put our pattern in a file in Hyperscan’s pattern format:

$ cat /tmp/pat

We put the corpus to be scanned in another file, with the same numeric identifier at the start to indicate that it should match pattern 1:

$ cat /tmp/corpus

Then we can run hscollider with its verbosity turned up (-vv) so that individual matches are displayed in the output:

$ bin/ue2collider -e /tmp/pat -c /tmp/corpus -Z 0 -T 1 -vv
ue2collider: The Pattern Collider Mark II

Number of threads:  1 (1 scanner, 1 generator)
Expression path:    /tmp/pat
Signature files:    none
Mode of operation:  block mode
UE2 scan alignment: 0
Corpora read from file: /tmp/corpus

Running single-pattern/single-compile test for 1 expressions.

PCRE Match @ (2,45)
PCRE Match @ (2,33)
PCRE Match @ (12,45)
PCRE Match @ (12,33)
UE2 Match @ (0,33) for 1
UE2 Match @ (0,45) for 1
Scan call returned 0
PASSED: id 1, alignment 0, corpus 0 (matched pcre:2, ue2:2)
Thread 0 processed 1 units.

Mode:                           Single/Block
Expressions processed:          1
Corpora processed:              1
Expressions with failures:      0
  Corpora generation failures:  0
  Compilation failures:         pcre:0, ng:0, ue2:0
  Matching failures:            pcre:0, ng:0, ue2:0
  Match differences:            0
  No ground truth:              0
Total match differences:        0

Total elapsed time: 0.00522815 secs.

We can see from this output that both PCRE and Hyperscan find matches ending at offset 33 and 45, and so hscollider considers this test case to have passed.

(In the example command line above, -Z 0 instructs us to only test at corpus alignment 0, and -T 1 instructs us to only use one thread.)


In default operation, PCRE produces only one match for a scan, unlike Hyperscan’s automata semantics. The hscollider tool uses libpcre’s “callout” functionality to match Hyperscan’s semantics.

Running a larger scan test

A set of patterns for testing purposes are distributed with Hyperscan, and these can be tested via hscollider on an in-tree build. Two CMake targets are provided to do this easily:

Make Target Description
make collide_quick_test Tests all patterns in streaming mode.
make collide_quick_test_block Tests all patterns in block mode.

Debugging: hsdump

When built in debug mode (using the CMake directive CMAKE_BUILD_TYPE set to Debug), Hyperscan includes support for dumping information about its internals during pattern compilation with the hsdump tool.

This information is mostly of use to Hyperscan developers familiar with the library’s internal structure, but can be used to diagnose issues with patterns and provide more information in bug reports.

Pattern Format

All of the Hyperscan tools accept patterns in the same format, read from plain text files with one pattern per line. Each line looks like this:

  • <integer id>:/<regex>/<flags>

For example:


The integer ID is the value that will be reported when a match is found by Hyperscan and must be unique.

The pattern itself is a regular expression in PCRE syntax; see Compiling Patterns for more information on supported features.

The flags are single characters that map to Hyperscan flags as follows:

Character API Flag Description
i HS_FLAG_CASELESS Case-insensitive matching
s HS_FLAG_DOTALL Dot (.) will match newlines
m HS_FLAG_MULTILINE Multi-line anchoring
H HS_FLAG_SINGLEMATCH Report match ID at most once
V HS_FLAG_ALLOWEMPTY Allow patterns that can match against empty buffers
8 HS_FLAG_UTF8 UTF-8 mode
W HS_FLAG_UCP Unicode property support
P HS_FLAG_PREFILTER Prefiltering mode
L HS_FLAG_SOM_LEFTMOST Leftmost start of match reporting
C HS_FLAG_COMBINATION Logical combination of patterns
Q HS_FLAG_QUIET Quiet at matching

In addition to the set of flags above, Extended Parameters can be supplied for each pattern. These are supplied after the flags as key=value pairs between braces, separated by commas. For example:


All Hyperscan tools will accept a pattern file (or a directory containing pattern files) with the -e argument. If no further arguments constraining the pattern set are given, all patterns in those files are used.

To select a subset of the patterns, a single ID can be supplied with the -z argument, or a file containing a set of IDs can be supplied with the -s argument.