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.

If set, causes pkg-config to print all kinds of debugging information and report all errors.

A value to set for the magic variable pc_top_builddir which may appear in .pc files. If the environ‐
ment 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.

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.

Don’t strip -I/usr/include out of cflags.

Don’t strip -L/usr/lib or -L/lib out of libs.

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/tar‐
get/usr/include/libfoo with a PKG_CONFIG_SYSROOT_DIR equal to /var/target (same rule apply to -L)

Replaces the default pkg-config search directory, usually /usr/lib/pkgconfig:/usr/share/pkgconfig.