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UniversalCodeGrep (ucg) is an extremely fast grep-like tool specialized for searching large bodies of source code.

Table of Contents


UniversalCodeGrep (ucg) is an extremely fast grep-like tool specialized for searching large bodies of source code. It is intended to be largely command-line compatible with Ack, to some extent with ag, and where appropriate with grep. Search patterns are specified as PCRE regexes.


ucg is intended to address the impatient programmer's code searching needs. ucg is written in C++20 and takes advantage of the concurrency (and other) support of the language to increase scanning speed while reducing reliance on third-party libraries and increasing portability. Regex scanning is provided by the PCRE2 library, with its JIT compilation feature providing a huge performance gain on most platforms. Directory tree traversal is performed by multiple threads, reducing the impact of waiting for I/O completions. Critical functions are implemented with hand-rolled vectorized (SSE2/4.2/etc.) versions selected at program load-time based on what the system supports, with non-vectorized fallbacks.

As a consequence of its overall design for maximum concurrency and speed, ucg is extremely fast. As an example, under Fedora 25, one of the benchmarks in the test suite which scans the Boost 1.58.0 source tree with ucg and a selection of similar utilities yields the following results:

Benchmark: '#include\s+".*"' on Boost source

Command Program Version Elapsed Real Time, Average of 10 Runs Num Matched Lines Num Diff Chars
/usr/bin/ucg --noenv --cpp '#include\s+.*' ~/src/boost_1_58_0 0.3.0 0.228973 9511 189
/usr/bin/rg -Lun -t cpp '#include\s+.*' ~/src/boost_1_58_0 0.2.9 0.167586 9509 0
/usr/bin/ag --cpp '#include\s+.*' ~/src/boost_1_58_0 0.32.0 2.29074 9511 189
grep -Ern --color --include=\*.cpp --include=\*.hpp --include=\*.h --include=\*.cc --include=\*.cxx '#include\s+.*' ~/src/boost_1_58_0 grep (GNU grep) 2.26 0.370082 9509 0

Note that UniversalCodeGrep is in fact somewhat faster than grep itself, even when grep is only using Extended Regular Expressions. And ucg certainly wins the ease-of-use contest.


GPL (Version 3 only)


UniversalCodeGrep packages are currently available for Fedora 23/24/25/26, Arch Linux, and OS X.

Fedora Copr Repository

If you are a Fedora user, the easiest way to install UniversalCodeGrep is from the Fedora Copr-hosted dnf/yum repository here. Installation is as simple as:

# Add the Copr repo to your system:
sudo dnf copr enable grvs/UniversalCodeGrep
# Install UniversalCodeGrep:
sudo dnf install universalcodegrep

Arch Linux User Repository

If you are a Arch Linux user, the easiest way to install UniversalCodeGrep is from the Arch Linux User Repository (AUR) here. Installation is as simple as:

# Install using yaourt:
yaourt -S ucg

Or you can install manually:

# Install manually:
cd /tmp/
curl -L -O
tar -xvf ucg.tar.gz
cd ycg
makepkg -sri


ucg has been accepted into homebrew-core, so installing it is as easy as:

brew install ucg

Building the Source Tarball

If a ucg package is not available for your platform, UniversalCodeGrep can be built and installed from the distribution tarball (available here) in the standard autotools manner:

tar -xaf universalcodegrep-0.3.3.tar.gz
cd universalcodegrep-0.3.3
make install

This will install the ucg executable in /usr/local/bin. If you wish to install it elsewhere or don't have permissions on /usr/local/bin, specify an installation prefix on the ./configure command line:

./configure --prefix=~/<install-root-dir>

*BSD Note

On at least PC-BSD 10.3, g++48 can't find its own libstdc++ without a little help. Configure the package like this:

./configure LDFLAGS='-Wl,-rpath=/usr/local/lib/gcc48'

Build Prerequisites

gcc and g++ versions 4.8 or greater.

Versions of gcc prior to 4.8 do not have sufficiently complete C++11 support to build ucg. clang/clang++ is also known to work, but is not the primary development compiler.

PCRE: libpcre2-8 version 10.20 or greater, or libpcre version 8.21 or greater.

One or both of these should be available from your Linux/OS X/*BSD distro's package manager. You'll need the -devel versions if they're packaged separately. Prefer libpcre2-8; while ucg will currently work with either PCRE2 or PCRE, you'll get better performance with PCRE2, and further development will be concentrated on PCRE2.

OS X Prerequisites

OS X additionally requires the installation of argp-standalone, which is normally part of the glibc library on Linux systems. This can be installed along with a pcre2 library from Homebrew:

$ brew update
$ brew install pcre2 argp-standalone

Supported OSes and Distributions

UniversalCodeGrep 0.3.3 should build and run on any reasonably POSIX-compliant platform where the prerequisites are available. It has been built and tested on the following OSes/distros:

  • Linux:
    • Fedora 23, 24, 25, 26
    • Arch Linux
    • Ubuntu 16.04 (Xenial), 14.04 (Trusty Tahr)
  • OS X:
    • OS X 10.10, 10.11, 10.12, with Xcode 6.4, 7.3.1, 8gm, 8.1, and 8.2 resp.
  • *BSDs:
    • TrueOS (nee PC-BSD) 12.0 (FreeBSD 12.0)
  • Windows:
    • Windows 7 + Cygwin 64-bit

Note that at this time, only x86-64/amd64 architectures are fully supported. 32-bit x86 builds are also occasionally tested.


Invoking ucg is the same as with ack or ag:


...where PATTERN is a PCRE-compatible regular expression.

If no FILES OR DIRECTORIES are specified, searching starts in the current directory.

Command Line Options

Version 0.3.3 of ucg supports a significant subset of the options supported by ack. In general, options specified later on the command line override options specified earlier on the command line.


Option Description
--[no]smart-case Ignore case if PATTERN is all lowercase (default: enabled).
-i, --ignore-case Ignore case distinctions in PATTERN.
-Q, --literal Treat all characters in PATTERN as literal.
-w, --word-regexp PATTERN must match a complete word.

Search Output

Option Description
--column Print column of first match after line number.
--nocolumn Don't print column of first match (default).

File presentation

Option Description
--color, --colour Render the output with ANSI color codes.
--nocolor, --nocolour Render the output without ANSI color codes.

File/directory inclusion/exclusion:

Option Description
--[no]ignore-dir=name, --[no]ignore-directory=name [Do not] exclude directories with this name.
--exclude=GLOB, --ignore=GLOB Files matching GLOB will be ignored.
--ignore-file=FILTER:FILTERARGS Files matching FILTER:FILTERARGS (e.g. ext:txt,cpp) will be ignored.
--include=GLOB Only files matching GLOB will be searched.
-k, --known-types Only search in files of recognized types (default: on).
-n, --no-recurse Do not recurse into subdirectories.
-r, -R, --recurse Recurse into subdirectories (default: on).
--type=[no]TYPE Include only [exclude all] TYPE files. Types may also be specified as --[no]TYPE: e.g., --cpp is equivalent to --type=cpp. May be specified multiple times.

File type specification:

Option Description
--type-add=TYPE:FILTER:FILTERARGS Files FILTERed with the given FILTERARGS are treated as belonging to type TYPE. Any existing definition of type TYPE is appended to.
--type-del=TYPE Remove any existing definition of type TYPE.
--type-set=TYPE:FILTER:FILTERARGS Files FILTERed with the given FILTERARGS are treated as belonging to type TYPE. Any existing definition of type TYPE is replaced.

Performance Tuning:

Option Description
--dirjobs=NUM_JOBS Number of directory traversal jobs (std::thread<>s) to use. Default is 2.
-j, --jobs=NUM_JOBS Number of scanner jobs (std::thread<>s) to use. Default is the number of cores on the system.


Option Description
--noenv Ignore .ucgrc files.

Informational options:

Option Description
-?, --help give this help list
--help-types, --list-file-types Print list of supported file types.
--usage give a short usage message
-V, --version print program version

Configuration (.ucgrc) Files

UniversalCodeGrep supports configuration files with the name .ucgrc, in which command-line options can be stored on a per-user and per-directory-hierarchy basis.


.ucgrc files are text files with a simple format. Each line of text can be either:

  1. A single-line comment. The line must start with a # and the comment continues for the rest of the line.
  2. A command-line parameter. This must be exactly as if it was given on the command line.

Location and Read Order

When ucg is invoked, it looks for command-line options from the following locations in the following order:

  1. The .ucgrc file in the user's $HOME directory, if any.
  2. The first .ucgrc file found, if any, by walking up the component directories of the current working directory. This traversal stops at either the user's $HOME directory or the root directory. This is called the project config file, and is intended to live in the top-level directory of a project directory hierarchy.
  3. The command line itself.

Options read later will override earlier options.

User-Defined File Types

ucg supports user-defined file types with the --type-set=TYPE:FILTER:FILTERARGS and --type-add=TYPE:FILTER:FILTERARGS command-line options. Three FILTERs are currently supported, ext (extension list), is (literal filename), and glob (glob pattern).

Extension List Filter

The extension list filter allows you to specify a comma-separated list of file extensions which are to be considered as belonging to file type TYPE. Example: --type-set=type1:ext:abc,xqz,def

Literal Filename Filter

The literal filename filter simply specifies a single literal filename which is to be considered as belonging to file type TYPE. Example:

Glob filter

The glob filter allows you to specify a glob pattern to match against filenames. If the glob matches, the file is considered as belonging to the file type TYPE. Example: --type-set=mk:glob:?akefile*


Gary R. Van Sickle