The standard build environment in the Nix Packages collection provides a environment for building Unix packages that does a lot of common build tasks automatically. In fact, for Unix packages that use the standard ./configure; make; make install build interface, you don’t need to write a build script at all; the standard environment does everything automatically. If stdenv doesn’t do what you need automatically, you can easily customise or override the various build phases.

To build a package with the standard environment, you use the function stdenv.mkDerivation, instead of the primitive built-in function derivation, e.g. stdenv.mkDerivation { name = "libfoo-1.2.3"; src = fetchurl { url = http://example.org/libfoo-1.2.3.tar.bz2; md5 = "e1ec107956b6ddcb0b8b0679367e9ac9"; }; } (stdenv needs to be in scope, so if you write this in a separate Nix expression from pkgs/all-packages.nix, you need to pass it as a function argument.) Specifying a name and a src is the absolute minimum you need to do. Many packages have dependencies that are not provided in the standard environment. It’s usually sufficient to specify those dependencies in the buildInputs attribute: stdenv.mkDerivation { name = "libfoo-1.2.3"; ... buildInputs = [libbar perl ncurses]; } This attribute ensures that the bin subdirectories of these packages appear in the PATH environment variable during the build, that their include subdirectories are searched by the C compiler, and so on. (See for details.) Often it is necessary to override or modify some aspect of the build. To make this easier, the standard environment breaks the package build into a number of phases, all of which can be overriden or modified individually: unpacking the sources, applying patches, configuring, building, and installing. (There are some others; see .) For instance, a package that doesn’t supply a makefile but instead has to be compiled “manually” could be handled like this: stdenv.mkDerivation { name = "fnord-4.5"; ... buildPhase = '' gcc foo.c -o foo ''; installPhase = '' ensureDir $out/bin cp foo $out/bin ''; } (Note the use of ''-style string literals, which are very convenient for large multi-line script fragments because they don’t need escaping of " and \, and because indentation is intelligently removed.) There are many other attributes to customise the build. These are listed in . While the standard environment provides a generic builder, you can still supply your own build script: stdenv.mkDerivation { name = "libfoo-1.2.3"; ... builder = ./builder.sh; } where the builder can do anything it wants, but typically starts with source $stdenv/setup to let stdenv set up the environment (e.g., process the buildInputs). If you want, you can still use stdenv’s generic builder: source $stdenv/setup buildPhase() { echo "... this is my custom build phase ..." gcc foo.c -o foo } installPhase() { ensureDir $out/bin cp foo $out/bin } genericBuild

The standard environment provides the following packages: The GNU C Compiler, configured with C and C++ support. GNU coreutils (contains a few dozen standard Unix commands). GNU findutils (contains find). GNU diffutils (contains diff, cmp). GNU sed. GNU grep. GNU awk. GNU tar. gzip and bzip2. GNU Make. It has been patched to provide nested output that can be fed into the nix-log2xml command and log2html stylesheet to create a structured, readable output of the build steps performed by Make. Bash. This is the shell used for all builders in the Nix Packages collection. Not using /bin/sh removes a large source of portability problems. The patch command. On Linux, stdenv also includes the patchelf utility.

NIX_DEBUG If set, stdenv will print some debug information during the build. In particular, the gcc and ld wrapper scripts will print out the complete command line passed to the wrapped tools. buildInputs A list of dependencies used by stdenv to set up the environment for the build. For each dependency dir, the directory dir/bin, if it exists, is added to the PATH environment variable. Other environment variables are also set up via a pluggable mechanism. For instance, if buildInputs contains Perl, then the lib/site_perl subdirectory of each input is added to the PERL5LIB environment variable. See for details. propagatedBuildInputs Like buildInputs, but these dependencies are propagated: that is, the dependencies listed here are added to the buildInputs of any package that uses this package as a dependency. So if package Y has propagatedBuildInputs = [X], and package Z has buildInputs = [Y], then package X will appear in Z’s build environment automatically.

The generic builder has a number of phases. Package builds are split into phases to make it easier to override specific parts of the build (e.g., unpacking the sources or installing the binaries). Furthermore, it allows a nicer presentation of build logs in the Nix build farm. Each phase can be overriden in its entirety either by setting the environment variable namePhase to a string containing some shell commands to be executed, or by redefining the shell function namePhase. The former is convenient to override a phase from the derivation, while the latter is convenient from a build script.

There are a number of variables that control what phases are executed and in what order: phases Specifies the phases. You can change the order in which phases are executed, or add new phases, by setting this variable. If it’s not set, the default value is used, which is $prePhases unpackPhase patchPhase $preConfigurePhases configurePhase $preBuildPhases buildPhase checkPhase $preInstallPhases installPhase fixupPhase $preDistPhases distPhase $postPhases. Usually, if you just want to add a few phases, it’s more convenient to set one of the variables below (such as preInstallPhases), as you then don’t specify all the normal phases. prePhases Additional phases executed before any of the default phases. preConfigurePhases Additional phases executed just before the configure phase. preBuildPhases Additional phases executed just before the build phase. preInstallPhases Additional phases executed just before the install phase. preDistPhases Additional phases executed just before the distribution phase. postPhases Additional phases executed after any of the default phases.

The unpack phase is responsible for unpacking the source code of the package. The default implementation of unpackPhase unpacks the source files listed in the src environment variable to the current directory. It supports the following files by default: Tar files These can optionally be compressed using gzip (.tar.gz, .tgz or .tar.Z) or bzip2 (.tar.bz2 or .tbz2). Zip files Zip files are unpacked using unzip. However, unzip is not in the standard environment, so you should add it to buildInputs yourself. Directories in the Nix store These are simply copied to the current directory. The hash part of the file name is stripped, e.g. /nix/store/1wydxgby13cz...-my-sources would be copied to my-sources. Additional file types can be supported by setting the unpackCmd variable (see below). srcs / src The list of source files or directories to be unpacked or copied. One of these must be set. sourceRoot After running unpackPhase, the generic builder changes the current directory to the directory created by unpacking the sources. If there are multiple source directories, you should set sourceRoot to the name of the intended directory. setSourceRoot Alternatively to setting sourceRoot, you can set setSourceRoot to a shell command to be evaluated by the unpack phase after the sources have been unpacked. This command must set sourceRoot. preUnpack Hook executed at the start of the unpack phase. postUnpack Hook executed at the end of the unpack phase. dontMakeSourcesWritable If set to 1, the unpacked sources are not made writable. By default, they are made writable to prevent problems with read-only sources. For example, copied store directories would be read-only without this. unpackCmd The unpack phase evaluates the string $unpackCmd for any unrecognised file. The path to the current source file is contained in the curSrc variable.

The patch phase applies the list of patches defined in the patches variable. patches The list of patches. They must be in the format accepted by the patch command, and may optionally be compressed using gzip (.gz) or bzip2 (.bz2). patchFlags Flags to be passed to patch. If not set, the argument -p1 is used, which causes the leading directory component to be stripped from the file names in each patch. prePatch Hook executed at the start of the patch phase. postPatch Hook executed at the end of the patch phase.

The configure phase prepares the source tree for building. The default unpackPhase runs ./configure (typically an Autoconf-generated script) if it exists. configureScript The name of the configure script. It defaults to ./configure if it exists; otherwise, the configure phase is skipped. This can actually be a command (like perl ./Configure.pl). configureFlags Additional arguments passed to the configure script. configureFlagsArray A shell array containing additional arguments passed to the configure script. You must use this instead of configureFlags if the arguments contain spaces. dontAddPrefix By default, the flag --prefix=$prefix is added to the configure flags. If this is undesirable, set this variable to a non-empty value. prefix The prefix under which the package must be installed, passed via the --prefix option to the configure script. It defaults to $out. dontAddDisableDepTrack By default, the flag --disable-dependency-tracking is added to the configure flags to speed up Automake-based builds. If this is undesirable, set this variable to a non-empty value. dontFixLibtool By default, the configure phase applies some special hackery to all files called ltmain.sh before running the configure script in order to improve the purity of Libtool-based packagesIt clears the sys_lib_*search_path variables in the Libtool script to prevent Libtool from using libraries in /usr/lib and such.. If this is undesirable, set this variable to a non-empty value. preConfigure Hook executed at the start of the configure phase. postConfigure Hook executed at the end of the configure phase.

The build phase is responsible for actually building the package (e.g. compiling it). The default buildPhase simply calls make if a file named Makefile, makefile or GNUmakefile exists in the current directory (or the makefile is explicitly set); otherwise it does nothing. makefile The file name of the Makefile. makeFlags Additional flags passed to make. These flags are also used by the default install and check phase. For setting make flags specific to the build phase, use buildFlags (see below). makeFlagsArray A shell array containing additional arguments passed to make. You must use this instead of makeFlags if the arguments contain spaces, e.g. makeFlagsArray=(CFLAGS="-O0 -g" LDFLAGS="-lfoo -lbar") Note that shell arrays cannot be passed through environment variables, so you cannot set makeFlagsArray in a derivation attribute (because those are passed through environment variables): you have to define them in shell code. buildFlags / buildFlagsArray Additional flags passed to make. Like makeFlags and makeFlagsArray, but only used by the build phase. preBuild Hook executed at the start of the build phase. postBuild Hook executed at the end of the build phase. You can set flags for make through the makeFlags variable. Before and after running make, the hooks preBuild and postBuild are called, respectively.

The check phase checks whether the package was built correctly by running its test suite. The default checkPhase calls make check, but only if the doCheck variable is enabled. doCheck If set to a non-empty string, the check phase is executed, otherwise it is skipped (default). Thus you should set doCheck = true; in the derivation to enable checks. makeFlags / makeFlagsArray / makefile See the build phase for details. checkTarget The make target that runs the tests. Defaults to check. checkFlags / checkFlagsArray Additional flags passed to make. Like makeFlags and makeFlagsArray, but only used by the check phase. preCheck Hook executed at the start of the check phase. postCheck Hook executed at the end of the check phase.

The install phase is responsible for installing the package in the Nix store under out. The default installPhase creates the directory $out and calls make install. makeFlags / makeFlagsArray / makefile See the build phase for details. installTargets The make targets that perform the installation. Defaults to install. Example: installTargets = "install-bin install-doc"; installFlags / installFlagsArray Additional flags passed to make. Like makeFlags and makeFlagsArray, but only used by the install phase. preInstall Hook executed at the start of the install phase. postInstall Hook executed at the end of the install phase.

The fixup phase performs some (Nix-specific) post-processing actions on the files installed under $out by the install phase. The default fixupPhase does the following: It moves the man/, doc/ and info/ subdirectories of $out to share/. It strips libraries and executables of debug information. On Linux, it applies the patchelf command to ELF executables and libraries to remove unused directories from the RPATH in order to prevent unnecessary runtime dependencies. It rewrites the interpreter paths of shell scripts to paths found in PATH. E.g., /usr/bin/perl will be rewritten to /nix/store/some-perl/bin/perl found in PATH. dontStrip If set, libraries and executables are not stripped. By default, they are. stripAllList List of directories to search for libraries and executables from which all symbols should be stripped. By default, it’s empty. Stripping all symbols is risky, since it may remove not just debug symbols but also ELF information necessary for normal execution. stripAllFlags Flags passed to the strip command applied to the files in the directories listed in stripAllList. Defaults to -s (i.e. --strip-all). stripDebugList List of directories to search for libraries and executables from which only debugging-related symbols should be stripped. It defaults to lib bin sbin. stripDebugFlags Flags passed to the strip command applied to the files in the directories listed in stripDebugList. Defaults to -S (i.e. --strip-debug). dontPatchELF If set, the patchelf command is not used to remove unnecessary RPATH entries. Only applies to Linux. dontPatchShebangs If set, scripts starting with #! do not have their interpreter paths rewritten to paths in the Nix store. forceShare The list of directories that must be moved from $out to $out/share. Defaults to man doc info. setupHook A package can export a setup hook by setting this variable. The setup hook, if defined, is copied to $out/nix-support/setup-hook. Environment variables are then substituted in it using substituteAll. preFixup Hook executed at the start of the fixup phase. postFixup Hook executed at the end of the fixup phase.

The distribution phase is intended to produce a source distribution of the package. The default distPhase first calls make dist, then it copies the resulting source tarballs to $out/tarballs/. This phase is only executed if the attribute doDist is not set. distTarget The make target that produces the distribution. Defaults to dist. distFlags / distFlagsArray Additional flags passed to make. tarballs The names of the source distribution files to be copied to $out/tarballs/. It can contain shell wildcards. The default is *.tar.gz. dontCopyDist If set, no files are copied to $out/tarballs/. preDist Hook executed at the start of the distribution phase. postDist Hook executed at the end of the distribution phase.

The standard environment provides a number of useful functions. ensureDir args Creates the specified directories, including all necessary parent directories, if they do not already exist. substitute infile outfile subs Performs string substitution on the contents of infile, writing the result to outfile. The substitutions in subs are of the following form: --replace s1 s2 Replace every occurence of the string s1 by s2. --subst-var varName Replace every occurence of @varName@ by the contents of the environment variable varName. This is useful for generating files from templates, using @...@ in the template as placeholders. --subst-var-by varName s Replace every occurence of @varName@ by the string s. Example: substitute ./foo.in ./foo.out \ --replace /usr/bin/bar $bar/bin/bar \ --replace "a string containing spaces" "some other text" \ --subst-var someVar substitute is implemented using the replace command. Unlike with the sed command, you don’t have to worry about escaping special characters. It supports performing substitutions on binary files (such as executables), though there you’ll probably want to make sure that the replacement string is as long as the replaced string. substituteInPlace file subs Like substitute, but performs the substitutions in place on the file file. substituteAll infile outfile Replaces every occurence of @varName@, where varName is any environment variable, in infile, writing the result to outfile. For instance, if infile has the contents #! @bash@/bin/sh PATH=@coreutils@/bin echo @foo@ and the environment contains bash=/nix/store/bmwp0q28cf21...-bash-3.2-p39 and coreutils=/nix/store/68afga4khv0w...-coreutils-6.12, but does not contain the variable foo, then the output will be #! /nix/store/bmwp0q28cf21...-bash-3.2-p39/bin/sh PATH=/nix/store/68afga4khv0w...-coreutils-6.12/bin echo @foo@ That is, no substitution is performed for undefined variables. stripHash path Strips the directory and hash part of a store path, and prints (on standard output) only the name part. For instance, stripHash /nix/store/68afga4khv0w...-coreutils-6.12 print coreutils-6.12.

The following packages provide a setup hook: GCC wrapper Adds the include subdirectory of each build input to the NIX_CFLAGS_COMPILE environment variable, and the lib and lib64 subdirectories to NIX_LDFLAGS. Perl Adds the lib/site_perl subdirectory of each build input to the PERL5LIB environment variable. Python Adds the lib/python2.5/site-packages subdirectory of each build input to the PYTHONPATH environment variable. This should be generalised: the Python version shouldn’t be hard-coded. pkg-config Adds the lib/pkgconfig and share/pkgconfig subdirectories of each build input to the PKG_CONFIG_PATH environment variable. Automake Adds the share/aclocal subdirectory of each build input to the ACLOCAL_PATH environment variable. libxml2 Adds every file named catalog.xml found under the xml/dtd and xml/xsl subdirectories of each build input to the XML_CATALOG_FILES environment variable. teTeX / TeX Live Adds the share/texmf-nix subdirectory of each build input to the TEXINPUTS environment variable. Qt Sets the QTDIR environment variable to Qt’s path. GHC Creates a temporary package database and registers every Haskell build input in it (TODO: how?).

[measures taken to prevent dependencies on packages outside the store, and what you can do to prevent them] GCC doesn't search in locations such as /usr/include. In fact, attempts to add such directories through the -I flag are filtered out. Likewise, the linker (from GNU binutils) doesn't search in standard locations such as /usr/lib. Programs built on Linux are linked against a GNU C Library that likewise doesn't search in the default system locations.