BEAR(1) - man page online | user commands

Build ear.

February 16, 2016
BEAR(1)                              General Commands Manual                              BEAR(1)


bear - build ear


bear [options] [build commands]


Bear is a tool to generate compilation database for clang tooling. The JSON compilation database ( is used in clang project to provide information how a single compilation unit was processed. When that is available then it is easy to re-run the compilation with different programs. Bear execs the original build command and intercept the exec calls. To achieve that Bear uses the LD_PRELOAD or DYLD_INSERT_LIBRARIES mechanisms provided by the dynamic linker. There is a library which defines the exec methods and used in every child processes of the build command. The executable itself sets the environment up to child processes and writes the output file.


-o output, --cdb output Specify output file. Default value provided. -a, --append Use previously generated output file and append the new entries to it. This way you can run bear continuously during work, and it keeps the compilation database up to date. File deletion and addition are both considered. But build process change (modifying compiler flags) will cause duplicate entries. -v, --verbose Make bear more verbose. -l library Specify the preloaded library location. Default value provided. (This option mainly for development purposes.) -n Disable filter. The output is also a JSON formated file. But the result is not a compilation database. It contains all available information of the exec calls. (This option mainly for development purposes.)


There are two version of output formats. One is defined by the clang tooling. This goes like this: [ { "directory": "/home/user/llvm/build", "command": "clang++ -Irelative -c -o file.o", "file": "" }, ... ] To achieve this bear has to run some filtering and formating. Build tools exec many com‐ mands during the build process. Bear has to find was that a compiler call, and what was the source file? The other output format is generated by the -n flag. (This output is not formalized, it's used to debug bear itself.)


Bear exit status is the exit status of the build command. Except when bear crashes, then it sets to non zero.


BEAR_OUTPUT The place of the temporary files where client shall report exec calls. Value set by bear, overrides previous value for child processes. LD_PRELOAD Used by the dynamic loader on Linux, FreeBSD and other UNIX OS. Value set by bear, overrides previous value for child processes. DYLD_INSERT_LIBRARIES Used by the dynamic loader on OS X. Value set by bear, overrides previous value for child processes. DYLD_FORCE_FLAT_NAMESPACE Used by the dynamic loader on OS X. Value set by bear, overrides previous value for child processes.


/usr/lib/i386-linux-gnu/bear/ bear library to implement exec calls.

SEE ALSO, exec(3)


Because Bear uses LD_PRELOAD or DYLD_INSERT_LIBRARIES environment variables, it does not append to it, but overrides it. So builds which are using these variables might not work. (I don't know any build tool which does that, but please let me know if you do.) Security extension/modes on different operating systems might disable library preloads. This case Bear behaves normaly, but the result compilation database will be empty. (Please make sure it's not the case when reporting bugs.) Notable examples for enabled security modes are: SIP on OS X Captain and SELinux on Fedora, CentOS, RHEL.
Copyright (C) 2012-2016 by László Nagy <>


László Nagy.
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