pkg-config
Return metainformation about installed libraries
Synopsis
pkg-config
[--modversion] [--help]
[--print-errors] [--silence-errors]
[--cflags] [--libs]
[--libs-only-L] [--libs-only-l]
[--cflags-only-I]
[--variable=VARIABLENAME]
[--define-variable=VARIABLENAME=VARIABLEVALUE]
[--print-variables] [--uninstalled]
[--exists]
[--atleast-version=VERSION]
[--exact-version=VERSION]
[--max-version=VERSION]
[--list-all] [LIBRARIES...]
[--print-provides]
[--print-requires]
[--print-requires-private] [LIBRARIES...]
add an example, a script, a trick and tips
examples
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description
The
pkg-config program is used to retrieve information
about installed libraries in the system. It is typically
used to compile and link against one or more libraries. Here
is a typical usage scenario in a Makefile:
program:
program.c
cc program.c $(pkg-config --cflags --libs gnomeui)
pkg-config
retrieves information about packages from special metadata
files. These files are named after the package, and has a
.pc extension. On most systems, pkg-config
looks in /usr/lib/pkgconfig, /usr/share/pkgconfig,
/usr/local/lib/pkgconfig and
/usr/local/share/pkgconfig for these files. It will
additionally look in the colon-separated (on Windows,
semicolon-separated) list of directories specified by the
PKG_CONFIG_PATH environment variable.
The package
name specified on the pkg-config command line is
defined to be the name of the metadata file, minus the
.pc extension. If a library can install multiple
versions simultaneously, it must give each version its own
name (for example, GTK 1.2 might have the package name
"gtk+" while GTK 2.0 has
"gtk+-2.0").
In addition to
specifying a package name on the command line, the full path
to a given .pc file may be given instead. This allows
a user to directly query a particular .pc file.
options
The following
options are supported:
--modversion
Requests that the version
information of the libraries specified on the command line
be displayed. If pkg-config can find all the
libraries on the command line, each library’s version
string is printed to stdout, one version per line. In this
case pkg-config exits successfully. If one or more
libraries is unknown, pkg-config exits with a nonzero
code, and the contents of stdout are undefined.
--help
Displays a help message and terminates.
--print-errors
If one or more of the modules
on the command line, or their dependencies, are not found,
or if an error occurs in parsing a .pc file, then
this option will cause errors explaining the problem to be
printed. With "predicate" options such as
"--exists" pkg-config runs silently by
default, because it’s usually used in scripts that
want to control what’s output. This option can be used
alone (to just print errors encountered locating modules on
the command line) or with other options. The
PKG_CONFIG_DEBUG_SPEW environment variable overrides this
option.
--silence-errors
If one or more of the modules
on the command line, or their dependencies, are not found,
or if an error occurs in parsing a a .pc file, then
this option will keep errors explaining the problem from
being printed. With "predicate" options such as
"--exists" pkg-config runs silently by
default, because it’s usually used in scripts that
want to control what’s output. So this option is only
useful with options such as "--cflags" or
"--modversion" that print errors by default. The
PKG_CONFIG_DEBUG_SPEW environment variable overrides this
option.
--errors-to-stdout
If printing errors, print them
to stdout rather than the default stderr
The following
options are used to compile and link programs:
--cflags
This prints pre-processor and
compile flags required to compile the packages on the
command line, including flags for all their dependencies.
Flags are "compressed" so that each identical flag
appears only once. pkg-config exits with a nonzero
code if it can’t find metadata for one or more of the
packages on the command line.
--cflags-only-I
This prints the -I part of
"--cflags". That is, it defines the header search
path but doesn’t specify anything else.
--libs
This option is identical to "--cflags", only
it prints the link flags. As with "--cflags",
duplicate flags are merged (maintaining proper ordering),
and flags for dependencies are included in the output.
--libs-only-L
This prints the -L/-R part of
"--libs". That is, it defines the library search
path but doesn’t specify which libraries to link
with.
--libs-only-l
This prints the -l part of
"--libs" for the libraries specified on the
command line. Note that the union of
"--libs-only-l" and "--libs-only-L" may
be smaller than "--libs", due to flags such as
-rdynamic.
--variable=VARIABLENAME
This returns the value of a
variable defined in a package’s .pc file. Most
packages define the variable "prefix", for
example, so you can say:
$ pkg-config --variable=prefix glib-2.0
/usr/
--define-variable=VARIABLENAME=VARIABLEVALUE
This sets a global value for a
variable, overriding the value in any .pc files. Most
packages define the variable "prefix", for
example, so you can say:
$ pkg-config --print-errors --define-variable=prefix=/foo \
--variable=prefix glib-2.0
/foo
--print-variables
Returns a list of all variables
defined in the package.
--uninstalled
Normally if you request the
package "foo" and the package
"foo-uninstalled" exists, pkg-config will
prefer the "-uninstalled" variant. This allows
compilation/linking against uninstalled packages. If you
specify the "--uninstalled" option,
pkg-config will return successfully if any
"-uninstalled" packages are being used, and return
failure (false) otherwise. (The
PKG_CONFIG_DISABLE_UNINSTALLED environment variable keeps
pkg-config from implicitly choosing
"-uninstalled" packages, so if that variable is
set, they will only have been used if you pass a name like
"foo-uninstalled" on the command line
explicitly.)
--exists
--atleast-version=VERSION
--exact-version=VERSION
--max-version=VERSION
These options test whether the
package or list of packages on the command line are known to
pkg-config, and optionally whether the version number
of a package meets certain constraints. If all packages
exist and meet the specified version constraints,
pkg-config exits successfully. Otherwise it exits
unsuccessfully.
Rather than
using the version-test options, you can simply give a
version constraint after each package name, for example:
$ pkg-config --exists ’glib-2.0 >= 1.3.4 libxml =
1.8.3’
Remember to use --print-errors if you want error
messages.
--msvc-syntax
This option is available only
on Windows. It causes pkg-config to output -l and -L
flags in the form recognized by the Microsoft Visual C++
command-line compiler, cl. Specifically, instead of
-Lx:/some/path it prints /libpath:x/some/path,
and instead of -lfoo it prints foo.lib. Note
that the --libs output consists of flags for the linker, and
should be placed on the cl command line after a /link
switch.
--dont-define-prefix
This option is available only
on Windows. It prevents pkg-config from automatically
trying to override the value of the variable
"prefix" in each .pc file.
--prefix-variable=PREFIX
Also this option is available
only on Windows. It sets the name of the variable that
pkg-config automatically sets as described above.
--static
Output libraries suitable for
static linking. That means including any private libraries
in the output. This relies on proper tagging in the .pc
files, else a too large number of libraries will ordinarily
be output.
--list-all
List all modules found in the
pkg-config path.
-I
"--print-provides"
List all modules the given
packages provides.
--print-requires
List all modules the given
packages requires.
--print-requires-private
List all modules the given
packages requires for static linking (see --static).
autoconf macros
PKG_CHECK_MODULES(VARIABLE-PREFIX, MODULES
[,ACTION-IF-FOUND
[,ACTION-IF-NOT-FOUND]])
The macro PKG_CHECK_MODULES can be used in configure.ac to
check whether modules exist. A typical usage would be:
PKG_CHECK_MODULES([MYSTUFF], [gtk+-2.0 >= 1.3.5 libxml =
1.8.4])
This would result in MYSTUFF_LIBS and MYSTUFF_CFLAGS substitution
variables, set to the libs and cflags for the given module list.
If a module is missing or has the wrong version, by default
configure will abort with a message. To replace the default
action, specify an ACTION-IF-NOT-FOUND. PKG_CHECK_MODULES will
not print any error messages if you specify your own
ACTION-IF-NOT-FOUND. However, it will set the variable
MYSTUFF_PKG_ERRORS, which you can use to display what went wrong.
Note that if there is a possibility the first call to
PKG_CHECK_MODULES might not happen, you should be sure to include
an explicit call to PKG_PROG_PKG_CONFIG in your configure.ac.
PKG_PROG_PKG_CONFIG([MIN-VERSION])
Defines the PKG_CONFIG variable to the best pkg-config available,
useful if you need pkg-config but don’t want to use
PKG_CHECK_MODULES.
PKG_CHECK_EXISTS(MODULES, [ACTION-IF-FOUND],
[ACTION-IF-NOT-FOUND])
Check to see whether a particular set of modules exists. Similar
to PKG_CHECK_MODULES(), but does not set variables or print
errors.
Similar to PKG_CHECK_MODULES, make sure that the first instance
of this or PKG_CHECK_MODULES is called, or make sure to call
PKG_CHECK_EXISTS manually.
environment variables
PKG_CONFIG_PATH
A colon-separated (on Windows, semicolon-separated) list of
directories to search for .pc files. The default directory will
always be searched after searching the path; the default is
libdir/pkgconfig:datadir/pkgconfig where
libdir is the libdir for pkg-config and
datadir is the datadir for pkg-config when it was
installed.
PKG_CONFIG_DEBUG_SPEW
If set, causes pkg-config to print all kinds of debugging
information and report all errors.
PKG_CONFIG_TOP_BUILD_DIR
A value to set for the magic variable pc_top_builddir
which may appear in .pc files. If the environment variable
is not set, the default value ’$(top_builddir)’ will be used.
This variable should refer to the top builddir of the Makefile
where the compile/link flags reported by pkg-config will
be used. This only matters when compiling/linking against a
package that hasn’t yet been installed.
PKG_CONFIG_DISABLE_UNINSTALLED
Normally if you request the package "foo" and the package
"foo-uninstalled" exists, pkg-config will prefer the
"-uninstalled" variant. This allows compilation/linking against
uninstalled packages. If this environment variable is set, it
disables said behavior.
PKG_CONFIG_ALLOW_SYSTEM_CFLAGS
Don’t strip -I/usr/include out of cflags.
PKG_CONFIG_ALLOW_SYSTEM_LIBS
Don’t strip -L/usr/lib out of libs
PKG_CONFIG_SYSROOT_DIR
Modify -I and -L to use the directories located in target
sysroot. this option is useful when cross-compiling packages that
use pkg-config to determine CFLAGS and LDFLAGS. -I and -L are
modified to point to the new system root. this means that a
-I/usr/include/libfoo will become
-I/var/target/usr/include/libfoo with a PKG_CONFIG_SYSROOT_DIR
equal to /var/target (same rule apply to -L)
PKG_CONFIG_LIBDIR
Replaces the default pkg-config search directory, usually
/usr/lib/pkgconfig
metadata file syntax
To add a library to the set of packages pkg-config knows
about, simply install a .pc file. You should install this
file to libdir/pkgconfig.
Here is an example file:
# This is a comment
prefix=/home/hp/unst # this defines a variable
exec_prefix=${prefix} # defining another variable in terms of the
first
libdir=${exec_prefix}/lib
includedir=${prefix}/include
Name: GObject # human-readable name
Description: Object/type system for GLib # human-readable
description
Version: 1.3.1
URL: http://www.gtk.org
Requires: glib-2.0 = 1.3.1
Conflicts: foobar <= 4.5
Libs: -L${libdir} -lgobject-1.3
Libs.private: -lm
Cflags: -I${includedir}/glib-2.0 -I${libdir}/glib/include
You would normally generate the file using configure, so that the
prefix, etc. are set to the proper values. The GNU Autoconf
manual recommends generating files like .pc files at build time
rather than configure time, so when you build the .pc file is a
matter of taste and preference.
Files have two kinds of line: keyword lines start with a keyword
plus a colon, and variable definitions start with an alphanumeric
string plus an equals sign. Keywords are defined in advance and
have special meaning to pkg-config; variables do not, you
can have any variables that you wish (however, users may expect
to retrieve the usual directory name variables).
Note that variable references are written "${foo}"; you can
escape literal "${" as "$${".
Name:
This field should be a human-readable name for the package. Note
that it is not the name passed as an argument to
pkg-config.
Description:
This should be a brief description of the package
URL:
An URL where people can get more information about and download
the package
Version:
This should be the most-specific-possible package version string.
Requires:
This is a comma-separated list of packages that are required by
your package. Flags from dependent packages will be merged in to
the flags reported for your package. Optionally, you can specify
the version of the required package (using the operators =, <,
>, >=, <=); specifying a version allows
pkg-config to perform extra sanity checks. You may only
mention the same package one time on the Requires: line.
If the version of a package is unspecified, any version will be
used with no checking.
Requires.private:
A list of packages required by this package. The difference from
Requires is that the packages listed under
Requires.private are not taken into account when a flag
list is computed for dynamically linked executable (i.e., when
--static was not specified). In the situation where each .pc file
corresponds to a library, Requires.private shall be used
exclusively to specify the dependencies between the libraries.
Conflicts:
This optional line allows pkg-config to perform additional
sanity checks, primarily to detect broken user installations. The
syntax is the same as Requires: except that you can list
the same package more than once here, for example "foobar =
1.2.3, foobar = 1.2.5, foobar >= 1.3", if you have reason to
do so. If a version isn’t specified, then your package conflicts
with all versions of the mentioned package. If a user tries to
use your package and a conflicting package at the same time, then
pkg-config will complain.
Libs:
This line should give the link flags specific to your package.
Don’t add any flags for required packages; pkg-config will
add those automatically.
Libs.private:
This line should list any private libraries in use. Private
libraries are libraries which are not exposed through your
library, but are needed in the case of static linking. This
differs from Requires.private in that it references
libraries that do not have package files installed.
Cflags:
This line should list the compile flags specific to your package.
Don’t add any flags for required packages; pkg-config will
add those automatically.
querying pkg-config s defaults
pkg-config can be used to query itself for the default
search path, version number and other information, for instance
using:
$ pkg-config --variable pc_path pkg-config
or
$ pkg-config --modversion pkg-config
windows specialities
If a .pc file is found in a directory that matches the usual
conventions (i.e., ends with \lib\pkgconfig or \share\pkgconfig),
the prefix for that package is assumed to be the grandparent of
the directory where the file was found, and the prefix
variable is overridden for that file accordingly.
If the value of a variable in a .pc file begins with the
original, non-overridden, value of the prefix variable,
then the overridden value of prefix is used instead.
bugs
pkg-config
does not handle mixing of parameters with and without =
well. Stick with one.
Bugs can be
reported at http://bugs.freedesktop.org/ under the
pkg-config component.
author
pkg-config
was written by James Henstridge, rewritten by Martijn van
Beers, and rewritten again by Havoc Pennington. Tim Janik,
Owen Taylor, and Raja Harinath submitted suggestions and
some code. gnome-config was written by Miguel de
Icaza, Raja Harinath and various hackers in the GNOME team.
It was inspired by Owen Taylor’s gtk-config
program.