「pkg-config」

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pkg-config – Return metainformation about installed libraries

SYNOPSIS

pkg-config [–modversion] [–version] [–help] [–atleast-pkgconfig-version=VERSION] [–print-errors]
[–short-errors] [–silence-errors] [–errors-to-stdout] [–debug] [–cflags] [–libs] [–libs-only-L]
[–libs-only-l] [–cflags-only-I] [–libs-only-other] [–cflags-only-other] [–variable=VARIABLENAME]
[–define-variable=VARIABLENAME=VARIABLEVALUE] [–print-variables] [–uninstalled] [–exists] [–atleast-ver‐
sion=VERSION] [–exact-version=VERSION] [–max-version=VERSION] [–validate] [–list-all] [–print-provides]
[–print-requires] [–print-requires-private] [LIBRARIES…]

DESCRIPTION

The pkg-config program is used to retrieve information about installed libraries in the system. It is typi‐
cally used to compile and link against one or more libraries. Here is a typical usage scenario in a Make‐
file:

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/pkg‐
config, /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.

–version

Displays the version of pkg-config and terminates.

–atleast-pkgconfig-version=VERSION

Requires at least the given version of pkg-config.

–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_CON‐

FIG_DEBUG_SPEW environment variable overrides this option.

–short-errors

Print short error messages.

–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_CON‐

FIG_DEBUG_SPEW environment variable overrides this option.

–errors-to-stdout

If printing errors, print them to stdout rather than the default stderr

–debug

Print debugging information. This is slightly different than the PKG_CONFIG_DEBUG_SPEW environment

variable, which also enable “–print-errors”.

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 pack‐

ages 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.

–cflags-only-other

This prints parts of “–cflags” not covered by “–cflags-only-I”.

–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 spec‐

ify 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 -rdy‐

namic.

–libs-only-other

This prints the parts of “–libs” not covered by “–libs-only-L” and “–libs-only-l”, such as

“–pthread”.

–variable=VARIABLENAME

This returns the value of a variable defined in a package’s .pc file. Most packages define the vari‐

able “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 com‐

mand 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-con‐

fig, and optionally whether the version number of a package meets certain constraints. If all pack‐

ages exist and meet the specified version constraints, pkg-config exits successfully. Otherwise it

exits unsuccessfully. Only the first VERSION comparing option will be honored. Subsequent options of

this type will be ignored.

Rather than using the version-test options, you can simply give a version constraint after each pack‐

age 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. When no output options are supplied to pkg-

config, –exists is implied.

–validate

Checks the syntax of a package’s .pc file for validity. This is the same as –exists except that

dependencies are not verified. This can be useful for package developers to test their .pc file prior

to release:
$ pkg-config –validate ./my-package.pc

–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.

–define-prefix
–dont-define-prefix

These options control whether pkg-config overrides the value of the variable prefix in each .pc file.

With –define-prefix, pkg-config uses the installed location of the .pc file to determine the prefix.

–dont-define-prefix prevents this behavior. The default is usually –define-prefix.

When this feature is enabled and a .pc file is found in a directory named pkgconfig, the prefix for

that package is assumed to be the grandparent of the directory where the file was found, and the pre‐

fix 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. This allows the feature to work even

when the variables have been expanded in the .pc file.

–prefix-variable=PREFIX

Set the name of the variable that pkg-config overrides instead of prefix when using the –define-pre‐

fix feature.

–static

Output libraries suitable for static linking. That means including any private libraries in the out‐

put. This relies on proper tagging in the .pc files, else a too large number of libraries will ordi‐

narily be output.

–list-all

List all modules found in the pkg-config path.

–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).

PKG-CONFIG DERIVED VARIABLES

pkg-config sets a few metadata variables that can be used in .pc files or queried at runtime.

pc_path

The default search path used by pkg-config when searching for .pc files. This can be used in a query

for the pkg-config module itself itself:
$ pkg-config –variable pc_path pkg-config

pcfiledir

The installed location of the .pc file. This can be used to query the location of the .pc file for a

particular module, but it can also be used to make .pc files relocatable. For instance:

prefix=${pcfiledir}/../..

exec_prefix=${prefix}

libdir=${exec_prefix}/lib

includedir=${prefix}/include

pc_sysrootdir

The sysroot directory set by the user. When the sysroot directory has not been set, this value is /.

See the PKG_CONFIG_SYSROOT_DIR environment variable for more details.

pc_top_builddir

Location of the user’s top build directory when calling pkg-config. This is useful to dynamically set

paths in uninstalled .pc files. See the PKG_CONFIG_TOP_BUILD_DIR environment variable for more

details.

WINDOWS SPECIALITIES

The pkg-config default search path is ignored on Windows. Instead, the search path is constructed by using
the installed directory of pkg-config and then appending lib\pkgconfig and share\pkgconfig. This can be aug‐
mented or replaced using the standard environment variables described above.

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 config‐

ure 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. How‐

ever, 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.

Also note that repeated usage of VARIABLE-PREFIX is not recommended. After the first successful

usage, subsequent calls with the same VARIABLE-PREFIX will simply use the _LIBS and _CFLAGS variables

set from the previous usage without calling pkg-config again.

PKG_PREREQ(MIN-VERSION)

Checks that the version of the pkg-config autoconf macros in use is at least MIN-VERSION. This can be

used to ensure a particular pkg-config macro will be available.

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_MODULES_STATIC(VARIABLE-PREFIX, MODULES [,ACTION-IF-FOUND [,ACTION-IF-NOT-FOUND]])

Enables static linking through –static prior to calling 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.

PKG_INSTALLDIR(DIRECTORY)

Substitutes the variable pkgconfigdir as the location where a module should install pkg-config .pc

files. By default the directory is $libdir/pkgconfig, but the default can be changed by passing DIREC‐

TORY. The user can override through the –with-pkgconfigdir parameter.

PKG_NOARCH_INSTALLDIR(DIRECTORY)

Substitutes the variable noarch_pkgconfigdir as the location where a module should install arch-inde‐

pendent pkg-config .pc files. By default the directory is $datadir/pkgconfig, but the default can be

changed by passing DIRECTORY. The user can override through the –with-noarch-pkgconfigdir parameter.

PKG_CHECK_VAR(VARIABLE, MODULE, CONFIG-VARIABLE, [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])

Retrieves the value of the pkg-config variable CONFIG-VARIABLE from MODULE and stores it in VARIABLE.

Note that repeated usage of VARIABLE is not recommended as the check will be skipped if the variable

is already set.

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 pack‐

ages; 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.

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.

参考文献

man 1 pkg-config, version 0.29