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<?xml version="1.0"?>
<guide self="ebuild-writing/variables/">
<chapter>
<title>Variables</title>
<body>
<p>
There are a number of special variables which must be set in ebuilds, and many
more which can optionally be specified. There are also some predefined variables
which are of use throughout the ebuild.
</p>
</body>
<section>
<title>Predefined Read-Only Variables</title>
<body>
<p>
The following variables are defined for you. You must not attempt to
set them. Developers must not rely on package manager specific values
for these variables when writing ebuilds.
</p>
<table>
<tr>
<th>Variable</th>
<th>Purpose</th>
</tr>
<tr>
<ti><c>P</c></ti>
<ti>Package name and version (excluding revision, if any), for example <c>vim-6.3</c>.</ti>
</tr>
<tr>
<ti><c>PN</c></ti>
<ti>Package name, for example <c>vim</c>.</ti>
</tr>
<tr>
<ti><c>PV</c></ti>
<ti>Package version (excluding revision, if any), for example <c>6.3</c>. It should reflect the upstream versioning scheme.</ti>
</tr>
<tr>
<ti><c>PR</c></ti>
<ti>Package revision, or <c>r0</c> if no revision exists.</ti>
</tr>
<tr>
<ti><c>PVR</c></ti>
<ti>Package version and revision (if any), for example <c>6.3</c>, <c>6.3-r1</c>.</ti>
</tr>
<tr>
<ti><c>PF</c></ti>
<ti>Full package name, <c>${PN}-${PVR}</c>, for example <c>vim-6.3-r1</c>.</ti>
</tr>
<tr>
<ti><c>A</c></ti>
<ti>
All the source files for the package (excluding those
which are not available because of <c>USE</c> flags).
</ti>
</tr>
<tr>
<ti><c>CATEGORY</c></ti>
<ti>Package's category, for example <c>app-editors</c>.</ti>
</tr>
<tr>
<ti><c>FILESDIR</c></ti>
<ti>
Path to the ebuild's <c>files/</c> directory, commonly used
for small patches and files. For example:
<c>"${PORTDIR}/${CATEGORY}/${PN}/files"</c>.
</ti>
</tr>
<tr>
<ti><c>WORKDIR</c></ti>
<ti>
Path to the ebuild's root build directory. For example:
<c>"${PORTAGE_BUILDDIR}/work"</c>.
</ti>
</tr>
<tr>
<ti><c>T</c></ti>
<ti>
Path to a temporary directory which may be used by the
ebuild. For example: <c>"${PORTAGE_BUILDDIR}/temp"</c>.
</ti>
</tr>
<tr>
<ti><c>D</c></ti>
<ti>
Path to the temporary install directory. For example:
<c>"${PORTAGE_BUILDDIR}/image"</c>.
</ti>
</tr>
<tr>
<ti><c>HOME</c></ti>
<ti>
Path to a temporary directory for use by any programs invoked by
an ebuild that may read or modify the home directory. For example:
<c>"${PORTAGE_BUILDDIR}/homedir"</c>.
</ti>
</tr>
<tr>
<ti><c>ROOT</c></ti>
<ti>
The absolute path to the root directory into which the package is to be
merged. Only allowed in pkg_* phases. See
<uri link="::ebuild-writing/variables#ROOT"/>
</ti>
</tr>
<tr>
<ti><c>DISTDIR</c></ti>
<ti>
Contains the path to the directory where all the files
fetched for the package are stored.
</ti>
</tr>
<tr>
<ti><c>EPREFIX</c></ti>
<ti>
The normalised offset-prefix path of an offset installation.
See <uri link="https://wiki.gentoo.org/wiki/Project:Prefix/Technical_Documentation">
Gentoo Prefix Technical Documentation</uri> for more information.
</ti>
</tr>
<tr>
<ti><c>ED</c></ti>
<ti>
Shorthand for <c>${D%/}${EPREFIX}/</c>.
</ti>
</tr>
<tr>
<ti><c>EROOT</c></ti>
<ti>
Shorthand for <c>${ROOT%/}${EPREFIX}/</c>.
</ti>
</tr>
<tr>
<ti><c>SYSROOT</c></ti>
<ti>
(EAPI=7) The absolute path to the root directory containing build dependencies
satisfied by <c>DEPEND</c>
</ti>
</tr>
<tr>
<ti><c>ESYSROOT</c></ti>
<ti>
(EAPI=7) Shorthand for <c>${SYSROOT%/}${EPREFIX}/</c>.
</ti>
</tr>
<tr>
<ti><c>BROOT</c></ti>
<ti>
(EAPI=7) The absolute path to the root directory containing build dependencies
satisfied by <c>BDEPEND</c>, typically executable build tools.
</ti>
</tr>
<tr>
<ti><c>MERGE_TYPE</c></ti>
<ti>
The type of package that is being merged. Possible values are:
<c>source</c> if building and installing a package from source,
<c>binary</c> if installing a binary package previously built from
the ebuild, <c>buildonly</c> if building a binary package without
installing it.
</ti>
</tr>
<tr>
<ti><c>REPLACING_VERSIONS</c></ti>
<ti>
A whitespace-separated list of all versions (<c>PVR</c>) of this package
that are being replaced (uninstalled or overwritten) as a result of this
install. It is a list, not a single optional value, to handle pathological
cases such as installing <c>foo-2:2</c> to replace <c>foo-2:1</c> and
<c>foo-3:2</c>. Available in <c>pkg_preinst</c> and <c>pkg_postinst</c>.
</ti>
</tr>
<tr>
<ti><c>REPLACED_BY_VERSION</c></ti>
<ti>
The single version (<c>PVR</c>) of this package that is replacing the
version provided by this ebuild, if it is being uninstalled as part of
an install. An empty string otherwise, i.e., if it is being uninstalled
without replacement. Available in <c>pkg_prerm</c> and <c>pkg_postrm</c>.
</ti>
</tr>
</table>
</body>
<subsection>
<title>ROOT</title>
<body>
<p>
The idea behind <c>ROOT</c> is that one can build a system with
<c>ROOT=/somewhere</c> and then chroot into it or tar up
<c>/somewhere</c> as a system image. It is not designed to allow the
user to run <c>/somewhere/usr/bin/foo</c>.
</p>
<p>
Ebuilds may reference <c>ROOT</c> only during <c>pkg_*</c> phases. It
can't be used correctly in <c>src_*</c> phases, since <c>ROOT</c> may
be different when merging a binary package. For example, a binary
package may be built with <c>ROOT=/</c> and then installed onto a
system using <c>ROOT=/somewhere</c>.
</p>
<p>
When building a package, <c>ROOT</c> should not be used to satisfy the
required dependencies on libraries, headers files etc. Instead, the
files on the build system should be specified using <c>/</c>.
</p>
<p>
In a cross compiling environment, ebuilds must not call any of the
binaries inside <c>ROOT</c> since they may not be executable on the
build system.
</p>
<p>
Below is an example of an ebuild that uses <c>ROOT</c> in
<c>pkg_postinst()</c> to conditionally print an error message if an
old and obsolete configuration file still exists:
</p>
<codesample lang="ebuild">
pkg_postinst() {
if [[ -e ${ROOT}/etc/oldconfig ]]; then
ewarn "You still have the obsolete config file"
ewarn " ${ROOT}/etc/oldconfig."
ewarn "Please migrate your settings to ${ROOT}/etc/newconfig"
ewarn "and remove ${ROOT}/etc/oldconfig."
fi
}
</codesample>
</body>
</subsection>
</section>
<section>
<title>Ebuild-defined Variables</title>
<body>
<p>
The following variables may or must be defined by every ebuild.
</p>
<table>
<tr>
<th>Variable</th>
<th>Purpose</th>
</tr>
<tr>
<ti><c>EAPI</c></ti>
<ti>
The EAPI. See <uri link="::ebuild-writing/eapi"/>.
</ti>
</tr>
<tr>
<ti><c>DESCRIPTION</c></ti>
<ti>
A short (not more than 80 characters) description of the package's
purpose. Mandatory.
</ti>
</tr>
<tr>
<ti><c>HOMEPAGE</c></ti>
<ti>
Package's homepage(s). Mandatory (except for virtuals), accepts
multiple values. In some contexts, it is customary to provide
package tracker and/or code hosting links besides the main homepage
(e.g. PyPI link for Python packages, GitHub link when code can't
easily be found on homepage) for convenience. If no homepage for
the package is available, please set it to
<c>https://wiki.gentoo.org/wiki/No_homepage</c>.
Never refer to a variable name in the string; include only raw text.
</ti>
</tr>
<tr>
<ti><c>SRC_URI</c></ti>
<ti>
A list of source URIs for the package. Can contain
<c>USE</c>-conditional parts, see
<uri link="::ebuild-writing/variables#SRC_URI"/>.
</ti>
</tr>
<tr>
<ti><c>LICENSE</c></ti>
<ti>
The package's license, corresponding exactly (including case)
to a file in <c>licenses/</c>. Mandatory (except for virtuals).
See <uri link="::ebuild-writing/variables#LICENSE"/>.
</ti>
</tr>
<tr>
<ti><c>SLOT</c></ti>
<ti>
The package's <c>SLOT</c>. Mandatory.
See <uri link="::ebuild-writing/variables#SLOT"/>.
</ti>
</tr>
<tr>
<ti><c>KEYWORDS</c></ti>
<ti>
See <uri link="::ebuild-writing/variables#KEYWORDS"/> and
<uri link="::keywording/"/>.
</ti>
</tr>
<tr>
<ti><c>IUSE</c></ti>
<ti>
A list of all <c>USE</c> flags (excluding arch flags, but
including <c>USE_EXPAND</c> flags) used within the ebuild. See
<uri link="::ebuild-writing/variables#IUSE"/>.
</ti>
</tr>
<tr>
<ti><c>REQUIRED_USE</c></ti>
<ti>
A list of assertions that must be met by the configuration of <c>USE</c>
flags to be valid for this ebuild.
See <uri link="::ebuild-writing/variables/#REQUIRED_USE"/>.
</ti>
</tr>
<tr>
<ti><c>PROPERTIES</c></ti>
<ti>
A space-delimited list of properties, with conditional syntax support.
<c>interactive</c>, <c>live</c>, and <c>test_network</c> are valid values.
</ti>
</tr>
<tr>
<ti><c>RESTRICT</c></ti>
<ti>
A space-delimited list of Portage features to restrict.
Valid values are <c>fetch</c>, <c>mirror</c>, <c>strip</c>, <c>test</c> and
<c>userpriv</c>. See <c>man 5 ebuild</c> for details.
</ti>
</tr>
<tr>
<ti><c>DEPEND</c></ti>
<ti>
A list of the package's build dependencies. See
<uri link="::general-concepts/dependencies"/>.
Starting with EAPI-7, applies to CHOST only.
</ti>
</tr>
<tr>
<ti><c>BDEPEND</c></ti>
<ti>
(EAPI=7) A list of the package's CBUILD build dependencies. See
<uri link="::general-concepts/dependencies"/>.
</ti>
</tr>
<tr>
<ti><c>RDEPEND</c></ti>
<ti>
A list of the package's runtime dependencies. See
<uri link="::general-concepts/dependencies"/>.
</ti>
</tr>
<tr>
<ti><c>PDEPEND</c></ti>
<ti>
A list of packages to be installed (if possible) after the package
is merged. Use this <e>only</e> when <c>RDEPEND</c> would cause cyclic
dependencies. See <uri link="::general-concepts/dependencies"/>.
</ti>
</tr>
<tr>
<ti><c>S</c></ti>
<ti>
Path to the temporary build directory, used by
<c>src_compile</c> and <c>src_install</c>. Default:
<c>"${WORKDIR}/${P}"</c>. Ebuilds should <b>not</b> provide a
value for this variable if it is the same as the default value.
</ti>
</tr>
<tr>
<ti><c>DOCS</c></ti>
<ti>
An array or whitespace-separated list of documentation files for
the default <c>src_install</c> function to install using <c>dodoc</c>.
If undefined, a reasonable default list is used. See the
<uri link="::ebuild-writing/functions/src_install/#Default src_install">
default <c>src_install</c> function</uri>.
</ti>
</tr>
<tr>
<ti><c>HTML_DOCS</c></ti>
<ti>
An array or space-delimited list of documentation files or
directories for the <c>einstalldocs</c> function to install
recursively. (Requires
<uri link="::ebuild-writing/eapi/#EAPI 6">EAPI>=6</uri>.)
</ti>
</tr>
</table>
</body>
<subsection>
<title>SRC_URI</title>
<subsubsection>
<title>Conditional Sources</title>
<body>
<p>
Conditional source files based upon USE flags are allowed using the usual
<c>flag? ( )</c> syntax. This is often useful for arch-specific code or for binary
packages <d/> downloading sparc binaries on ppc would be a waste of bandwidth.
</p>
<codesample lang="ebuild">
SRC_URI="https://example.com/files/${P}-core.tar.bz2
x86? ( https://example.com/files/${P}/${P}-sse-asm.tar.bz2 )
ppc? ( https://example.com/files/${P}/${P}-vmx-asm.tar.bz2 )
sparc? ( https://example.com/files/${P}/${P}-vis-asm.tar.bz2 )
doc? ( https://example.com/files/${P}/${P}-docs.tar.bz2 )"
</codesample>
</body>
</subsubsection>
<subsubsection>
<title>Renaming Sources</title>
<body>
<p>
Sometimes the upstream URI uses generic names that can easily clash with other
packages when creating a single mirror. Using the <c>-></c> syntax allows
you to rename the file when it's fetched from upstream for storing on mirrors
and in the local distdir.
</p>
<p>
Here we download a file from upstream which has a plain name like
<c>1.0.tar.gz</c> and save/mirror it with a better name like
<c>thepackage-1.0.tar.gz</c>. As usual, all tokens, including the operator
and the output file name, must be separated by whitespace.
</p>
<codesample lang="ebuild">
SRC_URI="https://example.com/files/${PV}.tar.gz -> ${P}.tar.gz"
</codesample>
</body>
</subsubsection>
<subsubsection>
<title>Third-party mirrors</title>
<body>
<p>
If the items in <c>SRC_URI</c> are available on multiple third-party mirrors,
and the same set of mirrors is shared across multiple ebuilds, then you
don't have to repeatedly list each of them in every ebuild.
The <c>profiles/thirdpartymirrors</c> file in the <c>::gentoo</c> repository
contains named groups of mirrors, in the format specified by the
Package Manager Specification (PMS), accessible through the
<c>mirror://</c>
pseudo-protocol.
</p>
<p>
One might define a set of "example" mirrors,
</p>
<pre>
example https://download.example.com https://mirror1.example.org/example
</pre>
<p>
that can afterwards be referenced through a <c>mirror://</c> URI:
</p>
<codesample lang="ebuild">
SRC_URI="mirror://example/${PN}/${P}.tar.gz"
</codesample>
<p>
There are two valid cases for using <c>thirdpartymirrors</c>:
</p>
<ol>
<li>
providing multiple download locations for mirror- or fetch-restricted
packages,
</li>
<li>
dealing with upstreams that distribute their distfiles via a network
of mirrors without a primary download location or a bouncer service.
</li>
</ol>
<p>
In any other case, the primary location must be used instead. The distfiles
will be <uri link="::general-concepts/mirrors">mirrored onto Gentoo
infrastructure</uri>; in that case, the benefit to using third-party mirror
list does not outweigh the burden of maintaining it.
</p>
</body>
</subsubsection>
<subsubsection>
<title>Lifting restrictions</title>
<body>
<p>
In EAPI 8, individual items in <c>SRC_URI</c> can be exempted from automatic
mirroring and fetching restrictions (imposed by <c>RESTRICT="mirror"</c> and
<c>RESTRICT="fetch"</c>) by prefixing the addresses with <c>mirror+</c> or
<c>fetch+</c>. For example, in the following ebuild,
</p>
<codesample lang="ebuild">
EAPI="8"
SRC_URI="${P}.tar.gz
mirror+https://dev.gentoo.org/~larry/distfiles/${P}-addons.tar.gz"
RESTRICT="fetch"
</codesample>
<p>
Portage will be prevented from trying to fetch <c>${P}.tar.gz</c> as expected,
but the <c>${P}-patches.tar.gz</c> file will be mirrored and fetched by Portage
without restriction.
</p>
<p>
The following table shows the effects of the prefixes when <c>RESTRICT="mirror"</c> and <c>RESTRICT="fetch"</c> are set:
</p>
<table>
<tr>
<th></th>
<th><e>(no prefix)</e></th>
<th><c>fetch+</c></th>
<th><c>mirror+</c></th>
</tr>
<tr>
<th><e>(no RESTRICT)</e></th>
<ti>fetch & mirror</ti>
<ti>fetch & mirror</ti>
<ti>fetch & mirror</ti>
</tr>
<tr>
<th><c>RESTRICT="mirror"</c></th>
<ti>fetch only</ti>
<ti>fetch only</ti>
<ti>fetch & mirror</ti>
</tr>
<tr>
<th><c>RESTRICT="fetch"</c></th>
<ti>unfetchable</ti>
<ti>fetch only</ti>
<ti>fetch & mirror</ti>
</tr>
</table>
</body>
</subsubsection>
</subsection>
<subsection>
<title>LICENSE</title>
<body>
<p>
It is possible to specify multiple <c>LICENSE</c> entries, and entries which only
apply if a particular <c>USE</c> flag is set. The format is the same as for
<c>DEPEND</c>. See <uri link="https://www.gentoo.org/glep/glep-0023.html">
GLEP 23</uri> for details.
</p>
</body>
</subsection>
<subsection>
<title>SLOT</title>
<body>
<p>
When slots are not needed, use <c>SLOT="0"</c>. Do <b>not</b> use
<c>SLOT=""</c>, because the variable must not be empty.
</p>
<p>
See <uri link="::general-concepts/slotting/" /> for more information on this
variable and see <uri link="::ebuild-maintenance/package-moves/" />.
</p>
</body>
</subsection>
<subsection>
<title>KEYWORDS</title>
<body>
<p>
The only valid construct involving a <c>*</c> inside <c>KEYWORDS</c> is a <c>-*</c>. Do
<b>not</b> use <c>KEYWORDS="*"</c> or <c>KEYWORDS="~*"</c>.
</p>
<p>
See <uri link="::keywording/"/> for how to handle this variable.
</p>
</body>
</subsection>
<subsection>
<title>IUSE</title>
<body>
<p>
Note that the <c>IUSE</c> variable is cumulative, so there is no need to specify
USE flags used only within inherited eclasses within the ebuild's IUSE.
</p>
<note>
You need not assign the IUSE variable in your ebuild if it is empty.
</note>
<p>
Arch USE flags (<c>sparc</c>, <c>mips</c>, <c>x64-macos</c> and so on) should
not be listed.
</p>
</body>
</subsection>
<subsection>
<title>REQUIRED_USE</title>
<body>
<p>
The <c>REQUIRED_USE</c> variable contains a list of assertions that must be
met by the configuration of USE flags to be valid for this ebuild. In order
to be matched, a USE flag in a terminal element must be enabled
(or disabled if it has an exclamation mark prefix).
</p>
<p>
Essentially, <c>REQUIRED_USE</c> is an analogue of <c>DEPEND</c> style syntax.
For example, to state that some combination is forbidden, i.e. "if foo is set,
bar must be unset":
</p>
<codesample lang="ebuild">
REQUIRED_USE="foo? ( !bar )"
</codesample>
<p>
To state "if foo is set, then at least one of bar, baz, and quux must be activated":
</p>
<codesample lang="ebuild">
REQUIRED_USE="foo? ( || ( bar baz quux ) )"
</codesample>
<p>
To state "exactly one of foo, bar, or baz must be set, but not several":
</p>
<codesample lang="ebuild">
REQUIRED_USE="^^ ( foo bar baz )"
</codesample>
<p>
Note that the last relationship is that of an Exclusive OR (XOR).
While an XOR could be formed from usual DEPEND syntax,
a specific ^^ operator has been added for this case.
</p>
<p>
Finally, to state "at least one of foo, bar, or baz must be set":
</p>
<codesample lang="ebuild">
REQUIRED_USE="|| ( foo bar baz )"
</codesample>
<important>
See section <uri link="::general-concepts/use-flags/#Conflicting USE Flags"/>
for when (and when not) to use <c>REQUIRED_USE</c>.
</important>
</body>
<subsubsection>
<title>EAPI 5</title>
<body>
<p>
EAPI 5 added an additional case to simplify conflicting USE flags.
</p>
<p>
To state "zero or one of foo, bar, or baz must be set, but not several":
</p>
<codesample lang="ebuild">
REQUIRED_USE="?? ( foo bar baz )"
</codesample>
<p>In the previous EAPI, this would be the same as:</p>
<codesample lang="ebuild">
REQUIRED_USE="foo? ( !bar !baz ) bar? ( !foo !baz ) baz? ( !foo !bar )"
</codesample>
</body>
</subsubsection>
</subsection>
<subsection>
<title>RESTRICT</title>
<body>
<p>
While Portage may recognise several different <c>RESTRICT</c> tokens, it is
important that you do not rely on them existing. That is, you should ensure
your ebuild does not fail if those tokens are not exposed or given a different
name by another package manager. You can make use of Portage-provided
<c>RESTRICT</c> tokens, but do not fail hard without them. See
<uri link="https://projects.gentoo.org/pms/7/pms.html#x1-810008.2.8">
PMS</uri> for the list of standardised <c>RESTRICT</c> tokens, or the above
table.
</p>
</body>
</subsection>
</section>
<section>
<title>Variables reserved for the package manager</title>
<body>
<p>
Variables and functions that begin with any of the following strings (ignoring
case) are reserved for package manager use. Ebuilds must neither use them nor
rely upon them:
</p>
<ul>
<li><c>__</c> (two underscores)</li>
<li><c>abort</c></li>
<li><c>dyn</c></li>
<li><c>prep</c></li>
</ul>
<p>
The same applies to functions and variables that contain any of the following
strings (ignoring case):
</p>
<ul>
<li>
<c>ebuild</c> (unless immediately preceded by another letter, and except
for the <c>EBUILD_PHASE</c> and <c>EBUILD_PHASE_FUNC</c> variables)
</li>
<li><c>hook</c></li>
<li><c>paludis</c></li>
<li><c>portage</c></li>
</ul>
</body>
</section>
<section>
<title>Version and Name Formatting Issues</title>
<body>
<p>
Often upstream's tarball versioning or naming format doesn't quite follow Gentoo
conventions. Using capital letters in names or differences in how underscores and hyphens
are used in versions are particularly common. For example, what Gentoo calls <c>foo-1.2.3b</c> may be
expecting a tarball named <c>Foo-1.2-3b.tar.bz2</c>. Rather than hard coding the package string,
it is preferable to make <c>MY_PN</c>, <c>MY_PV</c> and <c>MY_P</c> variables and use those to define the
upstream naming.
EAPI=7 debuted a new set of functions, ver_cut, ver_rs and ver_test.
These were backported into older EAPIs with the <c>eapi7-ver</c> eclass.
The easy way of redefining the version, which should be used unless you are sure
you know what you are doing, is to use these functions:
</p>
<codesample lang="ebuild">
inherit eapi7-ver
MY_PN="Foo"
# Replace the second period separator in PV with -
MY_PV=$(ver_rs 2 '-')
MY_P="${MY_PN}-${MY_PV}"
</codesample>
<p>
This code has the advantage that it will carry on working even if upstream
switches to a format like <c>Foo-1.3-4.5.tar.bz2</c> (yes, this really happens).
</p>
<p>
It is also possible to use bash substitution to achieve the same effect (this is
how eapi7-ver works internally), but this is complicated, error prone and hard
to read.
</p>
<p>
Some ebuilds use calls to <c>sed</c>, <c>awk</c> and / or <c>cut</c> to do this.
This must <e>not</e> be done for any new code and should be fixed to use
built-in version manipulation commands (for EAPI 7 or later), Bash substitution,
or in older EAPIs before 7, <c>eapi7-ver</c>. Global scope non-Bash code is
<e>strongly</e> discouraged.
</p>
<p>
The ver_ functions are used extract particular components
from a version string. See <c>man eapi7-ver.eclass</c> and the eclass source code
for further documentation and examples. A brief summary of the functions
follows.
</p>
<table>
<tr>
<th>Function</th>
<th>Purpose</th>
</tr>
<tr>
<ti><c>ver_rs [range] ' '</c></ti>
<ti>Get important version components, excluding '.', '-' and '_'.</ti>
</tr>
<tr>
<ti><c>ver_cut 1</c></ti>
<ti>Get the major version.</ti>
</tr>
<tr>
<ti><c>ver_cut [range]</c></ti>
<ti>Extract a range of subparts from a version string.</ti>
</tr>
<tr>
<ti><c>ver_cut 2-</c></ti>
<ti>Get everything after the major version.</ti>
</tr>
<tr>
<ti><c>ver_rs [range] [char]</c></ti>
<ti>Replace a particular version separator.</ti>
</tr>
<tr>
<ti><c>ver_rs 1- [char]</c></ti>
<ti>Replace all version separators.</ti>
</tr>
<tr>
<ti><c>ver_rs [range] ''</c></ti>
<ti>Delete a version separator.</ti>
</tr>
<tr>
<ti><c>ver_rs 1- ''</c></ti>
<ti>Delete all version separators.</ti>
</tr>
</table>
<note>
A helpful guide to the newer complements of the old <c>versionator.eclass</c>
functions can be found
<uri link="https://mgorny.pl/articles/the-ultimate-guide-to-eapi-7.html#replacing-versionator-eclass-uses">
here</uri>, courtesy of Gentoo developer mgorny.
</note>
</body>
</section>
<section>
<title>Trailing Slashes in Variables</title>
<body>
<p>
The following variables never end with a trailing slash in EAPI 7:
<c>D</c>, <c>ED</c>, <c>ROOT</c>, <c>EROOT</c>. Conversely, in EAPIs
preceeding EAPI 7, these variables are guaranteed to end with a
trailing slash. When working with EAPIs prior to EAPI 7, developers
are encouraged to use the bash suffix removal for the trailing slash
and add an explicit <c>/</c> when joining paths. For example:
<c>${D%/}/</c>, <c>${ED%/}/</c>, <c>${ROOT%/}/</c>,
<c>${EROOT%/}/</c>.
</p>
</body>
</section>
<section>
<title>Use of constant-value variables in ebuilds</title>
<body>
<p>
Variables have significant value in ebuilds, making it possible to avoid
unnecessary repetitions and make maintenance easier. However,
references to constant-value variables should be used with care as their
excessive use can harm readability and increase maintenance burden (e.g.
when renaming a package). In particular, using variables whose values
have no direct correlation with the expected string should be avoided.
</p>
<p>The examples of beneficial constant-value variable references are:</p>
<ul>
<li>
using <c>${PV}</c> and the variables derived from it (<c>${P}</c>,
<c>${MY_P}</c>…) in <c>SRC_URI</c> and <c>S</c> to avoid having
to update those variables for every version bump (assuming that
<c>${PV}</c> is used to indicate the upstream version);
</li>
<li>
using <c>${PF}</c> in <c>--docdir</c> path — this is a canonical
Gentoo path that is always required to match <c>${PF}</c>.
</li>
</ul>
<p>The examples of bad constant-value variable references are:</p>
<ul>
<li>
using <c>${PN}</c> in <c>HOMEPAGE</c>, <c>EGIT_REPO_URI</c>
or the domain of <c>SRC_URI</c> — it breaks URL parsing in editors
and terminals, and makes it hard to copy the link for external use
(e.g. while reviewing via gitweb),
</li>
<li>
using <c>${HOMEPAGE}</c> in <c>SRC_URI</c> — it breaks when homepage
changes or additional entry is added,
</li>
<li>
using <c>${PN}</c> (or other unnecessary helper variables)
excessively in <c>src_install()</c> — it impairs readability for
little benefit and causes a lot of trouble when the package needs to
be renamed.
</li>
</ul>
</body>
</section>
<section>
<title>User environment</title>
<body>
<p>
The following variables may be set in the user's environment and should be
respected by all ebuilds. The purpose of each variable within Gentoo is listed
alongside an example of a valid value. Upstream usage may diverge, but ebuilds
should ensure that these variables are interpreted consistently within Gentoo.
The chosen meanings are inspired by a few real and de-facto standards:
</p>
<ul>
<li>
<uri link="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/make.html">
The POSIX (2018) make specification</uri>
</li>
<li>
<uri link="https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html">
The GNU make (v4.3) implementation</uri>
</li>
<li>
<uri link="https://www.gnu.org/software/libtool/manual/libtool.html#LT_005fINIT">
The GNU libtool (v2.4.6) package</uri>
</li>
</ul>
<p>
Many of these variables only have an effect if they are invoked directly.
For example, your compiler driver is usually responsible for assembling object
files rather than a direct call to <c>${AS}</c>. In that case, setting
<c>ASFLAGS</c> will have no effect on the build process; instead, you would set
something like <c>CFLAGS="-Wa,-alh,-L"</c> to tell the C compiler to pass those
flags to the assembler. The <c>LDFLAGS</c> variable is the exception to this
rule, as it is intended to be passed to the compiler driver rather than
<c>${LD}</c>.
</p>
<table>
<tr>
<th>Variable</th>
<th>Purpose</th>
<th>Origin</th>
<th>Example</th>
</tr>
<tr>
<ti><c>AR</c></ti>
<ti>
<uri link="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ar.html">
ar</uri>-compatible library archiver
</ti>
<ti>POSIX make</ti>
<ti><c>x86_64-pc-linux-gnu-ar</c></ti>
</tr>
<tr>
<ti><c>ARFLAGS</c></ti>
<ti>flags for <c>${AR}</c></ti>
<ti>POSIX make</ti>
<ti><c>-v</c></ti>
</tr>
<tr>
<ti><c>AS</c></ti>
<ti>as-compatible assembler</ti>
<ti>GNU make</ti>
<ti><c>x86_64-pc-linux-gnu-as</c></ti>
</tr>
<tr>
<ti><c>ASFLAGS</c></ti>
<ti>flags for <c>${AS}</c></ti>
<ti>GNU make</ti>
<ti><c>--reduce-memory-overheads</c></ti>
</tr>
<tr>
<ti><c>CC</c></ti>
<ti>C compiler driver (also usually used for linking)</ti>
<ti>POSIX make</ti>
<ti><c>clang-9</c></ti>
</tr>
<tr>
<ti><c>CFLAGS</c></ti>
<ti>flags for <c>${CC}</c></ti>
<ti>POSIX make</ti>
<ti><c>-march=native</c></ti>
</tr>
<tr>
<ti><c>CPPFLAGS</c></ti>
<ti>flags for the C preprocessor</ti>
<ti>GNU make</ti>
<ti><c>-D_GNU_SOURCE</c></ti>
</tr>
<tr>
<ti><c>CXX</c></ti>
<ti>C++ compiler driver (also usually used for linking)</ti>
<ti>GNU make</ti>
<ti><c>clang++</c></ti>
</tr>
<tr>
<ti><c>CXXFLAGS</c></ti>
<ti>flags for <c>${CXX}</c></ti>
<ti>GNU make</ti>
<ti><c>-fvisibility=hidden</c></ti>
</tr>
<tr>
<ti><c>LD</c></ti>
<ti>dynamic linker</ti>
<ti>GNU libtool</ti>
<ti><c>x86_64-pc-linux-gnu-ld</c></ti>
</tr>
<tr>
<ti><c>LDFLAGS</c></ti>
<ti>flags for the <e>compiler driver</e> to pass to its linker</ti>
<ti>POSIX make</ti>
<ti><c>-Wl,-O1 -Wl,--as-needed</c></ti>
</tr>
<tr>
<ti><c>LEX</c></ti>
<ti>
<uri link="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/lex.html">
lex</uri>-compatible lexer
</ti>
<ti>POSIX make</ti>
<ti><c>/usr/bin/flex</c></ti>
</tr>
<tr>
<ti><c>LFLAGS</c></ti>
<ti>flags for <c>${LEX}</c></ti>
<ti>POSIX make</ti>
<ti><c>--8bit --posix-compat</c></ti>
</tr>
<tr>
<ti><c>NM</c></ti>
<ti>
<uri link="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/nm.html">
nm</uri>-compatible symbol extractor
</ti>
<ti>GNU libtool</ti>
<ti><c>x86_64-pc-linux-gnu-nm</c></ti>
</tr>
<tr>
<ti><c>RANLIB</c></ti>
<ti>archive index generator</ti>
<ti>GNU libtool</ti>
<ti><c>x86_64-pc-linux-gnu-ranlib</c></ti>
</tr>
<tr>
<ti><c>YACC</c></ti>
<ti>
<uri link="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/yacc.html">
yacc</uri>-compatible compiler-compiler
</ti>
<ti>POSIX make</ti>
<ti><c>/usr/bin/bison</c></ti>
</tr>
<tr>
<ti><c>YFLAGS</c></ti>
<ti>flags for <c>${YACC}</c></ti>
<ti>POSIX make</ti>
<ti><c>-d</c></ti>
</tr>
</table>
</body>
</section>
</chapter>
</guide>
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