tup(1)                            tup manual                            tup(1)

       tup - the updater

              tup [--debug-sql] [--debug-fuse] [SECONDARY_COMMAND] [ARGS]

       Tup is a file-based build system. You should use tup if you are
       developing software which needs to be translated from input files
       (written by you) into a different output format. For example, if you
       are writing a C program, you could use tup to determine which files
       need to be recompiled, archived, and linked based on a dependency

       Tup has no domain specific knowledge. You must tell tup how to build
       your program, such as by saying that all .c files are converted to .o
       files by using gcc. This is done by writing one or more Tupfiles.

       You can do all of your development with just 'tup', along with writing
       Tupfiles. See also the INI FILE, OPTIONS FILES and TUPFILES sections

       tup [<output_1> ... <output_n>]
              Updates the set of outputs based on the dependency graph and the
              current state of the filesystem. If no outputs are specified
              then the whole project is updated. This is what you run every
              time you make changes to your software to bring it up-to-date.
              You can run this anywhere in the tup hierarchy, and it will
              always update the requested output. By default, the list of
              files that are changed are determined by scanning the filesystem
              and checking modification times. For very large projects this
              may be slow, but you can skip the scanning time by running the
              file monitor (see SECONDARY COMMANDS for a description of the

              -jN    Temporarily override the updater.num_jobs option to 'N'.
                     This will run up to N jobs in parallel, subject to the
                     constraints of the DAG. Eg: 'tup -j2' will run up to two
                     jobs in parallel, whereas 'tup' will run up to
                     updater.num_jobs in parallel. See the option secondary
                     command below.

                     Causes tup to display the full command string instead of
                     just the pretty-printed string for commands that use the
                     ^ TEXT^ prefix.

                     Temporarily override the display.quiet option to '1'. See
                     the option secondary command below.

                     Temporarily override the updater.keep_going option to
                     '1'. See the option secondary command below.

                     Temporarily override the updater.keep_going option to
                     '0'. See the option secondary command below.

                     Do not scan the project for changed files. This is for
                     internal tup testing only, and should not be used during
                     normal development.

                     Do not check for updates to the environment variables
                     exported to sub-processes. Instead, the environment
                     variables will be used from the database. This is used by
                     the monitor in autoupdate/autoparse mode so that the most
                     recent environment variables are used, rather than the
                     settings when the monitor was initialized.

              -d     Output debug log to screen.

                     Output the :-rules generated by a run-script. See the
                     'run ./script args' feature in the TUPFILES section.
                     --debug-logging Save some debug output and build graphs
                     in .tup/log. Graphs are rotated on each invocation with

       These commands are used to modify the behavior of tup or look at its
       internals. You probably won't need these very often. Secondary commands
       are invoked as:

       tup [--debug-sql] [--debug-fuse] SECONDARY_COMMAND

       init [directory]
              Creates a '.tup' directory in the specified directory and
              initializes the tup database. If a directory name is
              unspecified, it defaults to creating '.tup' in the current
              directory. This defines the top of your project, as viewed by
              tup. Everything in the current directory and its subdirectories
              are known as the "tup hierarchy". You should not need to run
              this command directly, tup will automatically run init the first
              time it is run in a new directory, using Tupfile.ini to locate
              the project root.

                     Sets the 'db.sync' option of the project to '0'. By
                     default the 'db.sync' option will be set to '1'. This
                     flag is mostly used for test cases, but you could also
                     use this in any environment where you want to script tup
                     and use no synchronization by default.

       ref    The refactor command can be used to help refactor Tupfiles. This
              will cause tup to run through the parsing phase, but not execute
              any commands. If any Tupfiles that are parsed result in changes
              to the database, these are reported as errors. For example, we
              may have the following simple Tupfile:

              : foreach *.c |> gcc -c %f -o %o -Wall |> %B.o

              After an initial 'tup', we decide that we want to move the -Wall
              to a variable called CFLAGS. The Tupfile now looks like:

              CFLAGS = -Wall
              : foreach *.c |> gcc -c %f -o %o $(CFLAGS) |> %B.o

              Running 'tup refactor' will cause tup to parse the Tupfile, and
              if we made any mistakes, an error message will be displayed. The
              Tupfiles can then be modified to fix those errors, and keep
              running 'tup refactor' until all Tupfiles are parsed

              Errors are reported for adding or removing any of the following:
              commands, inputs that are generated files, outputs, the
              .gitignore directive, input or output <groups>, and directory
              level dependencies. Otherwise, you are able to move any strings
              out to $-variables, !-macros, and the like, so long as the end-
              result of the set of :-rules is the same.

              *LINUX ONLY* Starts the inotify-based file monitor. The monitor
              must scan the filesystem once and initialize watches on each
              directory. Then when you make changes to the files, the monitor
              will see them and write them directly into the database. With
              the monitor running, 'tup' does not need to do the initial scan,
              and can start constructing the build graph immediately. The
              "Scanning filesystem..." time from 'tup' is approximately equal
              to the time you would save by running the monitor. When the
              monitor is running, a 'tup' with no file changes should only
              take a few milliseconds (on my machines I get about 2 or 3ms
              when everything is in the disk cache). If you restart your
              computer, you will need to restart the monitor. The following
              arguments can be given on the command line. Any additional
              arguments not handled by the monitor will be passed along to the
              updater if either monitor.autoupdate or monitor.autoparse are
              enabled. For example, you could run the monitor as 'tup monitor
              -f -a -j2' to run the monitor in the foreground, and
              automatically update with 2 jobs when changes are detected. See
              also the option secondary command below.

              -d     Enable debugging of the monitor process.

                     Temporarily override the monitor.foreground option to 1.
                     The monitor will run in the foreground (don't daemonize).

                     Temporarily override the monitor.foreground option to 0.
                     The monitor will run in the background (daemonize).

                     Temporarily override the monitor.autoupdate option to 1.
                     This will automatically run an update when file changes
                     are detected.

                     Temporarily override the monitor.autoupdate option to 0.
                     This will prevent the monitor from automatically running
                     an update when file changes are detected.

                     Temporarily override the monitor.autoparse option to 1.
                     This will automatically run the parser when file changes
                     are detected.

                     Temporarily override the monitor.autoparse option to 0.
                     This will prevent the monitor from automatically running
                     the parser when file changes are detected.

       stop   Kills the monitor if it is running. Basically it saves you the
              trouble of looking up the PID and killing it that way.

       variant foo.config [bar.config] [...]
              For each argument, this command creates a variant directory with
              tup.config symlinked to the specified config file. For example,
              if a directory contained several variant configurations, one
              could easily create a variant for each config file:

              $ ls configs/
              $ tup variant configs/*.config
              tup: Added variant 'build-bar' using config file 'configs/bar.config'
              tup: Added variant 'build-foo' using config file 'configs/foo.config'

              This is equivalent to the following:

              $ mkdir build-bar
              $ ln -s ../configs/bar.config build-bar/tup.config
              $ mkdir build-foo
              $ ln -s ../configs/foo.config build-foo/tup.config

              For projects that commonly use several variants, the files in
              the configs/ directory could be checked in to source control.
              Each developer would run the 'tup variant' after 'tup init'
              during the initial checkout of the software. Variants can also
              be created manually by making a build directory and creating a
              tup.config file in it (see the VARIANTS section). This command
              merely helps save some steps, so that you don't have to make
              each build directory and tup.config symlink manually.

              Displays the current tup database configuration. These are
              internal values used by tup.

              Displays all of the current tup options, as well as where they

              For details on all of the available options and how to set them,
              see the OPTIONS FILES section below.

       graph [--dirs] [--ghosts] [--env] [--combine] [--stickies] [<output_1>
       ... <output_n>]
              Prints out a graphviz .dot format graph of the tup database to
              stdout. By default it only displays the parts of the graph that
              have changes. If you provide additional arguments, they are
              assumed to be files that you want to graph. This operates
              directly on the tup database, so unless you are running the file
              monitor you may want to run 'tup scan' first. This is generally
              used for debugging tup -- you may or may not find it helpful for
              trying to look at the structure of your program.

              --dirs Temporarily override the graph.dirs option to '1'. This
                     will show the directory nodes and Tupfiles.

                     Temporarily override the graph.ghosts option to '1'. This
                     will show ghost nodes (files that a command tried to
                     access, but don't actually exist).

              --env  Temporarily override the graph.environment option to '1'.
                     This will show the environment variables, such as PATH.

       todo [<output_1> ... <output_n>]
              Prints out the next steps in the tup process that will execute
              when updating the given outputs. If no outputs are specified
              then it prints the steps needed to update the whole project.
              Similar to the 'upd' command, 'todo' will automatically scan the
              project for file changes if a file monitor is not running.

                     Do not scan the project for changed files. This is for
                     internal tup testing only, and should not be used during
                     normal development.

                     Causes tup to display the full command string instead of
                     just the pretty-printed string for commands that use the
                     ^ TEXT^ prefix.

       generate [--config config-file] script.sh (or script.bat on Windows)
              The generate command will parse all Tupfiles and create a shell
              script that can build the program without running in a tup
              environment. The expected usage is in continuous integration
              environments that aren't compatible with tup's dependency
              checking (eg: if FUSE is not supported). On Windows, if the
              script filename has a ".bat" extension, then the output will be
              a batch script instead of a shell script. For example:

              git clone ... myproj
              cd myproj
              tup generate build.sh
              # Copy out build artifacts / logs here
              git clean -f -x -d

              The shell script does not work incrementally, so it is
              effectively a one-time use. You will need to clean up the tree
              before the next 'tup generate' and script invocation. This does
              not support variants, however the top-level tup.config file is
              used to define the configuration variables. Optionally, a
              separate configuration file can be passed in with the --config

       varsed The varsed command is used as a subprogram in a Tupfile; you
              would not run it manually at the command-line. It is used to
              read one file, and replace any variable references and write the
              output to a second file. Variable references are of the form
              @VARIABLE@, and are replaced with the corresponding value of the
              @-variable. For example, if foo.txt contains:

              The architecture is set to @ARCH@

              And you have a :-rule in a Tupfile like so:

              : foo.txt |> tup varsed %f %o |> foo-out.txt

              Then on an update, the output file will be identical to the
              input file, except the string @ARCH@ will be replaced with
              whatever CONFIG_ARCH is set to in tup.config. The varsed command
              automatically adds the dependency from CONFIG_ARCH to the
              particular command node that used it (so if CONFIG_ARCH changes,
              the output file will be updated with the new value).

       scan   You shouldn't ever need to run this, unless you want to make the
              database reflect the filesystem before running 'tup graph'. Scan
              is called automatically by 'upd' if the monitor isn't running.

       upd    Legacy secondary command. Calling 'tup upd' is equivalent to
              simply calling 'tup'.

       The tup command can be run from anywhere in the source tree. It uses
       the information from all Tupfiles (see the TUPFILES section) as well as
       it's own dynamic database, which is maintained in the .tup directory
       located at the root of the project. The .tup directory can be created
       manually with the "tup init" command, but it is much more common to use
       a Tupfile.ini, which can be added to the project's version control
       repository. Tup uses Tupfile.ini to identify the root of a project to
       automatically set up a .tup directory in the project root the first
       time it is run.

       The contents of the Tupfile.ini file are ignored.

       Tup allows for a variety of configuration files. These files affect the
       behavior of tup as a program, but not tup as a build system. That is to
       say, changing any of these options should not affect the end result of
       a successful build, but may affect how tup gets there (e.g. how many
       compile jobs to run in parallel).

       The options are read in the following precedence order:

         command-line overrides (eg: -j flag passed to 'tup')
         .tup/options file
         ~/.tupoptions file
         /etc/tup/options file
         tup's compiled in defaults

       For Windows, the options files are read in as follows:

         command-line overrides
         .tup/options file
         tup.ini in the Application Data path (usually C:\ProgramData\tup\tup.ini)
         tup's compiled in defaults

       For an exact list of paths on your platform, type 'tup options'.

       All files use the same .ini-style syntax. A section header is enclosed
       in square brackets, like so:

       The section header is followed by one or more variable definitions, of
       the form 'variable = value'. Comments start with a semi-colon and
       continue to the end of the line. The variable definitions can all be
       set to integers. For boolean flags, "true"/"yes" and "false"/"no" are
       synonyms for 1 and 0, respectively. For example, if you have a
       .tup/options file that contains:

            num_jobs = 2
            keep_going = true

       Then 'tup' will default to 2 jobs, and have the updater.keep_going flag
       set. The options listed below are of the form 'section.variable', so to
       set 'db.sync' you would need a '[db]' section followed by 'sync = 0',
       for example. The defaults listed here are the compiled-in defaults.

              db.sync (default '1')
                     Set to '1' if the SQLite synchronous feature is enabled.
                     When enabled, the database is properly synchronized to
                     the disk in a way that it is always consistent. When
                     disabled, it will run faster since writes are left in the
                     disk cache for a time before being written out. However,
                     if your computer crashes before everything is written
                     out, the tup database may become corrupted. See
                     http://www.sqlite.org/pragma.html for more information.

              updater.num_jobs (defaults to the number of processors on the
              system )
                     Set to the maximum number of commands tup will run
                     simultaneously. The default is dynamically determined to
                     be the number of processors on the system. If
                     updater.num_jobs is greater than 1, commands will be run
                     in parallel only if they are independent. See also the -j

              updater.keep_going (default '0')
                     Set to '1' to keep building as much as possible even if
                     errors are encountered. Anything dependent on a failed
                     command will not be executed, but other independent
                     commands will be. The default is '0', which will cause
                     tup to stop after the first failed command. See also the
                     -k option.

              updater.full_deps (defaults to '0')
                     Set to '1' to track dependencies on files outside of the
                     tup hierarchy. The default is '0', which only tracks
                     dependencies within the tup hierarchy. For example, if
                     you want all C files to be re-compiled when gcc is
                     updated on your system, you should set this to '1'. In
                     Linux and OSX, using full dependencies requires that the
                     tup binary is suid as root so that it can run sub-
                     processes in a chroot environment. Alternatively on
                     Linux, if your kernel supports user namespaces, then you
                     don't need to make the binary suid. Note that if this
                     value is set to '1' from '0', tup will rebuild the entire
                     project. Disabling this option when it was previously
                     enabled does not require a full rebuild, but does take
                     some time since the nodes representing external files are
                     cleared out. NOTE: This does not currently work with
                     ccache or other programs that may write to external files
                     due to issues with locking. This may be fixed in the

              updater.warnings (defaults to '1')
                     Set to '0' to disable warnings about writing to hidden
                     files. Tup doesn't track files that are hidden. If a sub-
                     process writes to a hidden file, then by default tup will
                     display a warning that this file was created. By
                     disabling this option, those warnings are not displayed.
                     Hidden filenames (or directories) include: ., .., .tup,
                     .git, .hg, .bzr, .svn.

              display.color (default 'auto')
                     Set to 'never' to disable ANSI escape codes for colored
                     output, or 'always' to always use ANSI escape codes for
                     colored output. The default is 'auto', which displays
                     uses colored output if stdout is connected to a tty, and
                     uses no colors otherwise (ie: if stdout is redirected to
                     a file).

              display.width (defaults to the terminal width)
                     Set to any number 10 or larger to force a fixed width for
                     the progress bar. This is assumed to be the total width,
                     some of which is used for spacing, brackets, and the
                     percentage complete. If this value is less than 10, the
                     progress bar is disabled.

              display.progress (defaults to '1' if stdout is a TTY)
                     Set to '1' to enable the progress bar, or '0' to turn it
                     off. By default it is enabled if stdout is a TTY, and
                     disabled if stdout is not a TTY.

              display.job_numbers (default '1')
                     Set to '0' to avoid displaying the "N) " string before
                     the results of a job. The default is to display this

              display.job_time (default '1')
                     Set to '0' to avoid displaying the runtime of a job along
                     with the results. The default is to display the runtime.
                     Note that the runtime displayed includes the time that
                     tup takes to save the dependencies. Therefore, this
                     runtime will likely be larger than the runtime when
                     executing the same job manually in the shell.

              display.quiet (default '0')
                     Set to '1' to prevent tup from displaying most output.
                     Tup will still display a banner and output from any job
                     that writes to stdout/stderr, or any job that returns a
                     non-zero exit code. The progress bar is still displayed;
                     see also display.progress for really quiet output.

              monitor.autoupdate (default '0')
                     Set to '1' to automatically rebuild if a file change is
                     detected. This only has an effect if the monitor is
                     running. The default is '0', which means you have to type
                     'tup' when you are ready to update.

              monitor.autoparse (default '0')
                     Set to '1' to automatically run the parser if a file
                     change is detected. This is similar to
                     monitor.autoupdate, except the update stops after the
                     parser stage - no commands are run until you manually
                     type 'tup'. This only has an effect if the monitor is
                     running. Note that if both autoupdate and autoparse are
                     set, then autoupdate takes precedence.

              monitor.foreground (default '0')
                     Set to '1' to run the monitor in the foreground, so
                     control will not return to the terminal until the monitor
                     is stopped (either by ctrl-C in the controlling terminal,
                     or running 'tup stop' in another terminal). The default
                     is '0', which means the monitor will run in the

              graph.dirs (default '0')
                     Set to '1' and the 'tup graph' command will show the
                     directory nodes and their ownership links. Tupfiles are
                     also displayed, since they point to directory nodes. By
                     default directories and Tupfiles are not shown since they
                     can clutter the graph in some cases, and are not always

              graph.ghosts (default '0')
                     Set to '1' to show ghost nodes. Some commands may try to
                     read from many files that don't exist, causing ghost
                     nodes to be created. By default, ghosts are not shown to
                     make the graph easier to understand.

              graph.environment (default '0')
                     Set to '1' to show the environment nodes (such as PATH)
                     and their dependencies. By default the environment
                     variables are not shown since nearly everything will
                     depend on PATH.

              graph.combine (default '0')
                     Set to '1' to try to combine similar nodes in the graph.
                     For example, instead of showing 10 separate compilation
                     commands that all have one .c file input and one .o file
                     output, this will combine them into one command to more
                     easily see the whole structure of the graph. By default
                     all nodes are shown separately.

       You must create a file called "Tupfile" anywhere in the tup hierarchy
       that you want to create an output file based on the input files. The
       input files can be anywhere else in the tup hierarchy, but the output
       file(s) must be written in the same directory as the Tupfile.

       : [foreach] [inputs] [ | order-only inputs] |> command |> [outputs] [ |
       extra outputs] [<group>] [{bin}]
              The :-rules are the primary means of creating commands, and are
              denoted by the fact that the ':' character appears in the first
              column of the Tupfile. The syntax is supposed to look somewhat
              like a pipeline, in that the input files on the left go into the
              command in the middle, and the output files come out on the

                     This is either the actual string "foreach", or it is
                     empty. The distinction is in how many commands are
                     generated when there are multiple input files. If
                     "foreach" is specified, one command is created for each
                     file in the inputs section. If it is not specified, one
                     command is created containing all of the files in the
                     inputs section. For example, the following Tupfiles are

                     # Tupfile 1
                     : foo.c |> gcc -c foo.c -o foo.o |> foo.o
                     : bar.c |> gcc -c bar.c -o bar.o |> bar.o

                     # Tupfile 2
                     : foreach foo.c bar.c |> gcc -c %f -o %o |> %B.o

                     Additionally, using "foreach" allows the use of the "%e"
                     flag (see below).

              inputs The input files for the command. An input file can be
                     anywhere in the tup hierarchy, and is specified relative
                     to the current directory. Input files affect the %-flags
                     (see below). Wildcarding is supported within a directory
                     by using the SQLite glob function. The special glob
                     characters are '*', '?', and '[]'. For example, "*.c"
                     would match any .c file, "fo?.c" would match any
                     3-character .c file that has 'f' and 'o' as the first two
                     characters, and "fo[xyz].c" would match fox.c, foy.c, and
                     foz.c. Globbing does not match directories, so "src/*.c"
                     will work, but "*/*.c" will not.

              order-only inputs
                     These are also used as inputs for the command, but will
                     not appear in any of the %-flags. They are separated from
                     regular inputs by use of the '|' character. In effect,
                     these can be used to specify additional inputs to a
                     command that shouldn't appear on the command line.
                     Globbing is supported as in the inputs section. For
                     example, one use for them is to specify auto-generated
                     header dependencies:

                     : |> echo "#define FOO 3" > %o |> foo.h
                     : foreach foo.c bar.c | foo.h |> gcc -c %f -o %o |> %B.o

                     This will add the foo.h dependency to the gcc commands
                     for foo.c and bar.c, so tup will know to generate the
                     header before trying to compile. The foreach command will
                     iterate over the regular inputs (here, foo.c and bar.c),
                     not the order-only inputs (foo.h). If you forget to add
                     such a dependency, tup will report an error when the
                     command is executed. Note that the foo.h dependency is
                     only listed here because it is created by another command
                     -- normal headers do not need to be specified.

                     The command string that will be passed to the system(3)
                     call by tup. This command is allowed to read from any
                     file specified as an input or order-only input, as well
                     as any other file in the tup hierarchy that is not the
                     output of another command. In other words, a command
                     cannot read from another command's output unless it is
                     specified as an input. This restriction is what allows
                     tup to be parallel safe. Additionally, the command must
                     write to all of the output files specified by the
                     "outputs" section, if any.

                     When executed, the command's file accesses are monitored
                     by tup to ensure that they conform to these rules. Any
                     files opened for reading that were generated from another
                     command but not specified as inputs are reported as
                     errors. Similarly, any files opened for writing that are
                     not specified as outputs are reported as errors. All
                     files opened for reading are recorded as dependencies to
                     the command. If any of these files change, tup will re-
                     execute the command during the next update. Note that if
                     an input listed in the Tupfile changes, it does not
                     necessarily cause the command to re-execute, unless the
                     command actually read from that input during the prior
                     execution. Inputs listed in the Tupfile only enforce
                     ordering among the commands, while file accesses during
                     execution determine when commands are re-executed.

                     A command string can begin with the special sequence
                     ^ TEXT^, which will tell tup to only print "TEXT" instead
                     of the whole command string when the command is being
                     executed. This saves the effort of using echo to pretty-
                     print a long command. The short-display behavior can be
                     overridden by passing the --verbose flag to tup, which
                     will cause tup to display the actual command string
                     instead of "TEXT". The space after the first '^' is
                     significant. Any characters immediately after the first
                     '^' are treated as flags. See the ^-flags section below
                     for details. For example, this command will print "CC
                     foo.c" when executing system(gcc -c foo.c -o foo.o) :

                     : foo.c |> ^ CC %f^ gcc -c %f -o %o |> foo.o

                     A command string can also begin with the special
                     character '!', in which case the !-macro specified will
                     be substituted in for the actual command. See the !-macro
                     definition later. Commands can also be blank, which is
                     useful to put all the input files in a {bin} for a later

                     The outputs section specifies the files that will be
                     written to by the command. Only one command can write to
                     a specific file, but a single command can output multiple
                     files (such as how a bison command will output both a .c
                     and .h file). The output can use any %-flags except %o.
                     Once a file is specified in an output section, it is put
                     into the tup database. Any following rules can use that
                     file as an input, even if it doesn't exist in the
                     filesystem yet.

                     The extra-outputs section is similar to the order-only
                     inputs section. It is separated from the regular outputs
                     by the '|' character. The extra-outputs behave exactly as
                     regular outputs, except they do not appear in the %o
                     flag. These can be used if a command generates files
                     whose names do not actually appear in the command line.
                     If there is exactly one output specified by the rule, the
                     extra-outputs section can use the %O flag to represent
                     the basename of the output. This can be useful in extra-
                     outputs for !-macros.

                     Output files can be grouped into global groups by
                     specifying a <group> after the outputs but before a bin.
                     Groups allow for order-only dependencies between folders.
                     Note that groups are directory specific, however, so when
                     referring to a group you must specify the path to where
                     it is assigned. For example, if a main project depends on
                     the output from several submodules you can structure Tup
                     like so to make sure the submodules are built before the
                     main project:

                     : foo.c |> gcc -c %f -o %o |> %B.o ../<submodgroup>

                     : bar.c |> gcc -c %f -o %o |> %B.o ../<submodgroup>

                     : baz.c | ../submodules/<submodgroup> |> gcc -c %f -o %o |> %B.o

                     Notice how groups are directory specific and the path is
                     specified outside of the <>. By specifying the
                     <submodgroup> as an order-only input Tup will build the
                     submodules before attempting to build the entire project.

              {bin}  Outputs can be grouped into a bin using the "{bin}"
                     syntax. A later rule can use "{bin}" as an input to use
                     all of the files in that bin. For example, the foreach
                     rule will put each .o file in the objs bin, which is used
                     as an input in the linker rule:

                     : foreach *.c |> gcc -c %f -o %o |> %B.o {objs}
                     : {objs} |> gcc %f -o %o |> program

                     In this case one could use *.o as the input instead, but
                     sometimes it is useful to separate outputs into groups
                     even though they have the same extension (such as if one
                     directory creates multiple binaries, using *.o wouldn't
                     be correct). If a {bin} is specified in the output
                     section of multiple rules, the bin will be the union of
                     all the outputs. You can't remove things from a bin, and
                     the bin disappears after the current Tupfile is parsed.

              In a command string that uses the ^ TEXT^ sequence, flag
              characters can be placed immediately after the ^ until the first
              space character or closing caret. For example:

              : foo.c |> ^c CC %f^ gcc --coverage %f -o %o |> foo | foo.gcno
              : bar.c |> ^c^ gcc --coverage %f -o %o |> bar | bar.gcno

              In the foo.c case, the command requires namespaces (or suid) and
              will display "CC foo.c". In the bar.c case, the command requires
              namespaces (or suid) and the "gcc --coverage bar.c -o bar"
              string is displayed. These are the supported flag characters:

              b      The 'b' flag causes the command to be run via
                     "/usr/bin/env bash -e -o pipefail -c <command>" instead
                     of the default "/bin/sh -e -c <command>". In addition to
                     allowing bash extensions in the :-rule, "-o pipefail"
                     dictates that "the return value of a pipeline is the
                     value of the last (rightmost) command to exit with a non-
                     zero status, or zero if all commands in the pipeline exit

              c      The 'c' flag causes the command to fail if tup does not
                     support user namespaces (on Linux) or is not suid root.
                     In these cases, tup runs in a degraded mode where the
                     fake working directories are visible in the sub-
                     processes, and some dependencies may be missed. If these
                     degraded behaviors will break your a particular command
                     in your build, add the 'c' flag so that users know they
                     need to add the suid bit or upgrade their kernel. This
                     flag is ignored on Windows.

              o      The 'o' flag causes the command to compare the new
                     outputs against the outputs from the previous run. Any
                     outputs that are the same will not cause dependent
                     commands in the DAG to be executed. For example, adding
                     this flag to a compilation command will skip the linking
                     step if the object file is the same from the last time it

              Within a command string or output string, the following %-flags
              may also be used to substitute values from the inputs or

              %%     Expands to a single "%" character in the command string.
                     This should be used when you want the percent character
                     to be interpreted by the command itself rather than by
                     tup's parser.

              %f     The filename from the "inputs" section. This includes the
                     path and extension. This is most useful in a command,
                     since it lists each input file name with the path
                     relative to the current directory. For example,
                     "src/foo.c" would be copied exactly as "src/foo.c"

              %b     Like %f, but is just the basename of the file. The
                     directory part is stripped off. For example, "src/foo.c"
                     would become "foo.c"

              %B     Like %b, but strips the extension. This is most useful in
                     converting an input file into an output file of the same
                     name but with a different extension, since the output
                     file needs to be in the same directory. For example,
                     "src/foo.c" would become "foo"

              %e     The file extension of the current file when used in a
                     foreach rule. This can be used for variables that can
                     have different values based on the suffix of the file.
                     For example, you could set certain flags for assembly
                     (.S) files that are different from .c files, and then use
                     a construct like $(CFLAGS_%e) to reference the CFLAGS_S
                     or CFLAGS_c variable depending on what type of file is
                     being compiled. For example, "src/foo.c" would become
                     "c", while "src/foo.S" would become "S"

              %o     The name of the output file(s). It is useful in a command
                     so that the filename passed to a command will always
                     match what tup thinks the output is. This only works in
                     the "command" section, not in the "outputs" section.

              %O     The name of the output file without the extension. This
                     only works in the extra-outputs section if there is
                     exactly one output file specified. A use-case for this is
                     if you have a !-macro that generates files not specified
                     on the command line, but are based off of the output that
                     is named. For example, if a linker creates a map file by
                     taking the specified output "foo.so", removing the ".so"
                     and adding ".map", then you may want a !-macro like so:

                     !ldmap = |> ld ... -o %o |> | %O.map
                     : foo1.o foo2.o |> !ldmap |> foo.so

              %d     The name of the lowest level of the directory. For
                     example, in foo/bar/Tupfile, this would be the string
                     "bar". One case where this can be useful is in naming
                     libraries based on the directory they are in, such as
                     with the following !-macro:

                     !ar = |> ar crs %o %f |> lib%d.a

                     Using this macro in foo/bar/Tupfile would then create

              %g     The string that a glob operator matched. For example with
                     the files a_text.txt and b_text.txt, the rule:

                     : foreach *_text.txt |> foo %f |> %g_binary.bin

                     will output the filenames a_binary.bin and b_binary.bin.
                     Only the first glob expanded will be substituted in for
                     %g. %g is only valid when there is a single input file or
                     foreach is used.

                     All of the files in "group". For example:

                     : foo.c |> gcc -c %f -o %o |> %B.o ../<submodgroup>

                     : bar.c |> gcc -c %f -o %o |> %B.o ../<submodgroup>

                     : ../submodules/<submodgroup> |> echo '%f' > %o |> submodules_f.txt
                     : ../submodules/<submodgroup> |> echo '%<submodgroup>' > %o |> submodules_group.txt

                     will produce "../submodules/<submodgroup>" in
                     submodules_f.txt, but "../submodules/sm1/foo.o
                     ../submodules/sm2/bar.o" in submodules_group.txt. If the
                     input contains multiple groups with the same name but
                     different directories, %<group> will be expanded to all
                     of the files in each listed group.

       var = value
       var := value
              Set the $-variable "var" to the value on the right-hand side.
              Both forms are the same, and are allowed to more easily support
              converting old Makefiles. The $-variable "var" can later be
              referenced by using "$(var)". Variables referenced here are
              always expanded immediately. As such, setting a variable to have
              a %-flag does not make sense, because a %-flag is only valid in
              a :-rule. The syntax $(var_%e) is allowed in a :-rule. Variable
              references do not nest, so something like $(var1_$(var2)) does
              not make sense. You also cannot pass variable definitions in the
              command line or through the environment. Any reference to a
              variable that has not had its value set returns an empty string.

              CFLAGS = -Dfoo
              : bar.c |> cc $(CFLAGS) $(other) -o %o -c %f |> %B.o

              will generate the command "cc -Dfoo  -o bar.o -c bar.c" when

       Any $-variable that begins with the string "CONFIG_" is automatically
       converted to the @-variable of the same name minus the "CONFIG_"
       prefix. In other words, $(CONFIG_FOO) and @(FOO) are interchangeable.
       Attempting to assign a value to a CONFIG_ variable in a Tupfile results
       in an error, since these can only be set in the tup.config file.

       Note that you may see a syntax using back-ticks when setting variables,
       such as:

       CFLAGS += `pkg-config fuse --cflags`

       Tup does not do any special processing for back-ticks, so the pkg-
       config command is not actually executed when the variable is set in
       this example. Instead, this is passed verbatim to any place that uses
       it. Therefore if a command later references $(CFLAGS), it will contain
       the string `pkg-config fuse --cflags`, so it will be parsed by the

       var += value
              Append "value" to the end of the current value of "var". If
              "var" has not been set, this is equivalent to a regular '='
              statement. If "var" already has a value, a space is appended to
              the $-variable before the new value is appended.

              The special $-variable TUP_CWD is always set to the path
              relative to the Tupfile currently parsed. It can change value
              when including a file in a different directory. For example, if
              you "include ../foo.tup", then TUP_CWD will be set to ".." when
              parsing foo.tup. This lets foo.tup specify flags like "CFLAGS +=
              -I$(TUP_CWD)", and CFLAGS will always have the -I directory
              where foo.tup is located, no matter if it was included as
              "../foo.tup" or "../../foo.tup" or "subdir/foo.tup". For an
              alternative to $(TUP_CWD) when referring to files, see the
              section on &-variables below.

       No other special $-variables exist yet, but to be on the safe side you
       should assume that all variables named TUP_* are reserved.

       &var = file
       &var := file
       &var += file
              p.PD 1 Set the &-variable to refer to the given file or
              directory. The file must be a normal file, not a generated file
              (an output from a :-rule). &-variables are used to refer to
              files in a similar way as $(TUP_CWD), except that instead of
              storing the relative path to the file, &-variables store tup's
              internal ID of the file. This means that the relative path to
              the file is determined when the &-variable is used, rather than
              when the variable is assigned as is the case with $(TUP_CWD).
              &-variables can only be used in the following locations: :-rule
              inputs, :-rule order-only inputs, :-rule commands, include
              lines, and run-script lines, and they are later be referenced by
              using "&(var)".

              # Tuprules.tup
              &libdir = src/lib
              !cc = |> cc -I&(libdir) -c %f -o %o |> %B.o

              # src/lib/Tupfile
              : foreach *.c |> !cc |>
              : *.o |> ar crs %o %f |> libstuff.a

              # src/lib/test/Tupfile
              : test_stuff.c |> !cc |>
              : test_stuff.o &(libdir)/libstuff.a |> cc -o %o %f |> test_stuff

              # src/Tupfile
              : main.c |> !cc |> main.o
              : main.o &(libdir)/libstuff.a |> cc -o %o %f |> main_app

              will generate the following build.sh commands (via "tup generate

              cd src/lib
              cc -I. -c lib1.c -o lib1.o
              cc -I. -c lib2.c -o lib2.o
              ar crs libstuff.a lib1.o lib2.o
              cd test
              cc -I.. -c test_stuff.c -o test_stuff.o
              cc -o test_stuff test_stuff.o ../libstuff.a
              cd ../..
              cc -Ilib -c main.c -o main.o
              cc -o main_app main.o lib/libstuff.a

       ifeq (lval,rval)
              Evaluates the 'lval' and 'rval' parameters (ie: substitutes all
              $-variables and @-variables), and does a string comparison to
              see if they match. If so, all lines between the 'ifeq' and
              following 'endif' statement are processed; otherwise, they are
              ignored. Note that no whitespace is pruned for the values - all
              text between the '(' and ',' comprise 'lval', and all text
              between the ',' and ')' comprise 'rval'. This means that ifeq
              (foo, foo) is false, while ifeq (foo,foo) is true. This is for
              compatibility with Makefile if statements.

              ifeq (@(FOO),y)
              CFLAGS += -DFOO
              CFLAGS += -g

       ifneq (lval,rval)
              Same as 'ifeq', but with the logic inverted.
       ifdef VARIABLE
              Tests of the @-variable named VARIABLE is defined at all in
              tup.config. If so, all lines between the 'ifdef' and following
              'endif' statement are processed; otherwise, they are ignored.
              For example, suppose tup.config contains:


              Then 'ifdef FOO' will evaluate to true. If tup.config doesn't
              exist, or does not set CONFIG_FOO in any way, then 'ifdef FOO'
              will be false.
       ifndef VARIABLE
              Same as 'ifdef', but with the logic inverted.
       else   Toggles the true/false-ness of the previous if-statement.
       endif  Ends the previous ifeq/ifdef/ifndef. Note that only 8 levels of
              nesting if-statements is supported.
       error [message]
              Causes tup to stop parsing and fail, printing message to the
              user as explanation.
       !macro = [inputs] | [order-only inputs] |> command |> [outputs]
              Set the !-macro to the given command string. This syntax is very
              similar to the :-rule, since a !-macro is basically a macro for
              those rules. The !-macro is not expanded until it is used in the
              command string of a :-rule. As such, the primary use of the
              !-macro is to have a place to store command strings with %-flags
              that may be re-used. For example, we could have a !cc macro in a
              top-level Tuprules.tup file like so:

              !cc = |> ^ CC %f^ gcc -c %f -o %o |>

              A Tupfile could then do as follows:

              : foreach *.c |> !cc |> %B.o

              You will only want to specify the output parameter in either the
              !-macro or the :-rule that uses it, but not both. If you specify
              any inputs in the !-macro, they would usually be order-only
              inputs. For example, if you have a !cc rule where you are using
              a compiler that has been generated by tup, you can list the
              compiler file in the order-only list of the !-macro. The
              compiler file will then become an input dependency for any
              :-rule that uses the macro.
       include file
              Reads the specified file and continues parsing almost as if that
              file was pasted inline in the current Tupfile. Only regular
              files are allowed to be included -- attempting to include a
              generated file is an error. Any include statements that occur in
              the included file will be parsed relative to the included file's
              Reads in Tuprules.tup files up the directory chain. The first
              Tuprules.tup file is read at the top of the tup hierarchy,
              followed by the next subdirectory, and so on through to the
              Tuprules.tup file in the current directory. In this way, the
              top-level Tuprules.tup file can specify general variable
              settings, and subsequent subdirectories can override them with
              more specific settings. You would generally specify
              include_rules as the first line in the Tupfile. The name is a
              bit of a misnomer, since you would typically use Tuprules.tup to
              define variables rather than :-rules.
       run ./script args
              Runs an external script with the given arguments to generate
              :-rules. This is an advanced feature that can be used when the
              standard Tupfile syntax is too simplistic for a complex program.
              The script is expected to write the :-rules to stdout. No other
              Tupfile commands are allowed - for example, the script cannot
              create $-variables or !-macros, but it can output :-rules that
              use those features. As a simple example, consider if a command
              must be executed 5 times, but there are no input files to use
              tup's foreach keyword. An external script called 'build.sh'
              could be written as follows:

              #! /bin/sh -e
              for i in `seq 1 5`; do
                   echo ": |> echo $i > %o |> $i.txt"

              A Tupfile can then be used to get these rules:

              run ./build.sh

              Tup will then treat this as if a Tupfile was written with 5
              lines like so:

              : |> echo 1 > %o |> 1.txt
              : |> echo 2 > %o |> 2.txt
              : |> echo 3 > %o |> 3.txt
              : |> echo 4 > %o |> 4.txt
              : |> echo 5 > %o |> 5.txt

              Since the Tupfile-parsing stage is watched for dependencies, any
              files that this script accesses within the tup hierarchy will
              cause the Tupfile to be re-parsed. There are some limitations,
              however. First, the readdir() call is instrumented to return the
              list of files that would be accessible at that time that the
              run-script starts executing. This means the files that you see
              in 'ls' on the command-line may be different from the files that
              your script sees when it is parsed. Tup essentially pretends
              that the generated files don't exist until it parses a :-rule
              that lists it as an output. Note that any :-rules executed by
              the run-script itself are not parsed until the script executes
              successfully. Second, due to some structural limitations in tup,
              the script cannot readdir() on any directory other than the
              directory of the Tupfile. In other words, a script can do 'for i
              in *.c', but not 'for i in sub/*.c'. The '--debug-run' flag can
              be passed to 'tup' in order to show the list of :-rules that tup
              receives from the script. Due to the readdir() instrumentation,
              this may be different than the script's output when it is run
              manually from the command-line.

       preload directory
              By default, a run-script can only use a readdir() (ie: use a
              wild-card) on the current directory. To specify a list of other
              allowable wild-card directories, use the preload keyword. For
              example, if a run script needs to look at *.c and src/*.c, the
              src directory needs to be preloaded:

              preload src
              run ./build.sh *.c src/*.c

       export VARIABLE
              The export directive adds the environment variable VARIABLE to
              the export list for future :-rules and run-scripts. The value
              for the variable comes from tup's environment, not from the
              Tupfile itself. Generally this means you will need to set the
              variable in your shell if you want to change the value used by
              commands and scripts. By default only PATH is exported. Windows
              additionally exports several variables suitable for building
              with the Visual Studio compiler suite. Tup will check the
              exported environment variables to see if they have changed
              values between updates, and re-execute any commands that that
              use those environment variables. Note that this means if PATH is
              changed, all commands will run again. For example:

              : |> command1 ... |>
              export FOO
              : |> command2 ... |>

              Tup will save the current value of FOO and pass it to the
              environment when executing command2. If FOO has a different
              value during the next update, then command2 will execute again
              with the new value in the environment. In this example, command1
              will not have FOO in its environment and will not re-execute
              when its value changes.

              Note that the FOO above is passed to the environment; it is not
              provided as an internal variable within tup. Thus, given the

              export FOO
              : |> echo myFOO=$(FOO) envFOO=${FOO} > %o |> foo.txt

              when run as "$ FOO=silly tup" would result in the contents of
              the foo.txt file being "myFOO= envFOO=silly". If the "export
              FOO" was removed from the Tupfile, the contents of the file
              would be "myFOO= envFOO=" because tup does not propagate
              environment variables unless they are explicitly exported. This
              helps preserve repeatable and deterministic builds.

              If you wish to export a variable to a specific value rather than
              get the value from the environment, you can do that in your
              shell instead of through tup. For example, in Linux you can do:

              : |> FOO=value command ... |>

              This usage will not create a dependency on the environment
              variable FOO, since it is controlled through the Tupfile.

              Tells tup to automatically generate a .gitignore file in the
              current directory which contains a list of the output files that
              are generated by tup. This can be useful if you are using git,
              since the set of files generated by tup matches exactly the set
              of files that you want git to ignore. If you are using
              Tuprules.tup files, you may just want to specify .gitignore in
              the top-level Tuprules.tup, and then have every other Tupfile
              use include_rules to pick up the .gitignore definition. In this
              way you never have to maintain the .gitignore files manually.
              Note that you may wish to ignore other files not created by tup,
              such as temporary files created by your editor. In this case
              case you will want to setup a global gitignore file using a
              command like 'git config --global core.excludesfile
              ~/.gitignore', and then setup ~/.gitignore with your personal
              list. For other cases, you can also simply add any custom ignore
              rules above the "##### TUP GITIGNORE #####" line.
       #      At the beginning of a line, a '#' character signifies a comment.
              A comment line is ignored by the parser. The comment can have
              leading whitespaces that is also ignored. If there is any non-
              whitespace before a '#' character, then the line is not a
              comment. It also means that if a previous line ended with '\'
              (line wrap) then '#' is interpreted as a regular symbol.

       Variable expansion in tup is immediate in every case except for
       !-macros. That is, if you see a :-rule or variable declaration, you can
       substitute the current values for the variables. The !-macros are only
       parsed when they used in a :-rule. In that case, the actual :-rule is a
       sort of a union between the :-rule as written and the current value of
       the !-macro.
       When tup parses a Tupfile, it makes a single pass through the file,
       parsing a line at a time. At the end of the Tupfile, all variable,
       !-macro, and {bin} definitions are discarded. The only lingering
       effects of parsing a Tupfile are the command nodes and dependencies
       that now exist in the tup database. Additionally, a .gitignore file may
       have been created if requested by the Tupfile.

       @-variables are special variables in tup. They are used as
       configuration variables, and can be read by Tupfiles or used by the
       varsed command. Commands are able to read them too, but the program
       executed by the command has to have direct knowledge of the variables.
       @-variables are specified in the tup.config file at the top of the tup
       hierarchy or in a variant directory. For example, tup.config may


       A Tupfile may then read the @-variable like so:

       srcs-@(FOO) += foo.c
       srcs-y += bar.c
       : foreach $(srcs-y) |> gcc -c %f -o %o |> %B.o

       In this example, if CONFIG_FOO is set to 'y', then the foo.c file will
       be included in the input list and therefore compiled. If CONFIG_FOO is
       unspecified or set to some other value, foo.c will not be included.
       The @-variables can be used similar to $-variables, with the following
       distinctions: 1) @-variables are read-only in Tupfiles, and 2)
       @-variables are in the DAG, which means reading from them creates a
       dependency from the @-variable to the Tupfile. Therefore any Tupfile
       that reads @(FOO) like the above example will be reparsed if the value
       of CONFIG_FOO in tup.config changes.
       The reason for prefixing with "CONFIG_" in the tup.config file is to
       maintain compatibility with kconfig, which can be used to generate this
       Note that the syntax for tup.config is fairly strict. For a statement
       like "CONFIG_FOO=y", tup will create an @-variable using the string
       starting after "CONFIG_", and up to the '=' sign. The value is
       everything immediately after the '=' sign until the newline, but if
       there is a surrounding pair of quotes, they are stripped. In this
       example, it would set "FOO" to "y". Note that if instead the line were
       "CONFIG_FOO = y", then the variable "FOO " would be set to " y".
       In tup.config, comments are determined by a '#' character in the first
       column. These are ignored, unless the comment is of the form:

       # CONFIG_FOO is not set

       In this case, the @-variable "FOO" is explicitly set to "n".
              TUP_PLATFORM is a special @-variable. If CONFIG_TUP_PLATFORM is
              not set in the tup.config file, it has a default value according
              to the platform that tup itself was compiled in. Currently the
              default value is one of "linux", "solaris", "macosx", "win32",
              or "freebsd".
              TUP_ARCH is another special @-variable. If CONFIG_TUP_ARCH is
              not set in the tup.config file, it has a default value according
              to the processor architecture that tup itself was compiled in.
              Currently the default value is one of "i386", "x86_64",
              "powerpc", "powerpc64", "ia64", "alpha", "sparc", "arm64", or

       Tup supports variants, which allow you to build your project multiple
       times with different configurations. Perhaps the most common case is to
       build a release and a debug configuration with different compiler
       flags, though any number of variants can be used to support whatever
       configurations you like. Each variant is built in its own directory
       distinct from each other and from the source tree. When building with
       variants, the in-tree build is disabled. To create a variant, make a
       new directory at the top of the tup hierarchy and create a "tup.config"
       file there. For example:

       $ mkdir build-default
       $ touch build-default/tup.config
       $ tup

       Here we created a directory called "build-default" and made an empty
       tup.config inside. Note that the build directory must be at the same
       level as the ".tup" directory. Upon updating, tup will parse all of the
       Tupfiles using the configuration file we created, and place all build
       products within subdirectories of build-default that mirror the source
       tree. We could then create another variant like so:

       $ mkdir build-debug
       $ echo "CONFIG_MYPROJ_DEBUG=y" > build-debug/tup.config
       $ tup

       This time all Tupfiles will be parsed with @(MYPROJ_DEBUG) set to "y",
       and all build products will be placed in the build-debug directory.
       Note that setting @(MYPROJ_DEBUG) only has any effect if the variable
       is actually used in a Tupfile (perhaps by adding debug flags to the
       compiler command-line).

       Running "tup" will update all variants. For example, updating after
       modifying a C file that is used in all configurations will cause it to
       be re-compiled for each variant. As with any command that is executed,
       this is done in parallel subject to the constraints of the DAG and the
       number of jobs specified. To build a single variant (or subset of
       variants), specify the build directory as the target to "tup", just
       like with any partial update. For example:

       $ tup build-default

       To delete a variant, just wipe out the build directory:

       $ rm -rf build-debug

       If you build with variants, it is recommended that you always have a
       default variant that contains an empty tup.config file. This helps
       check that your software is always able to be built by simply checking
       it out and doing 'tup init; tup' without relying on a specific

       When using in-tree builds, the resulting build outputs may rely on run-
       time files, placed in the source tree and not being processed by tup.
       Tup allows such files to be copied verbatim in the variant build
       directory by providing a built-in macro "!tup_preserve":

       :foreach *.png |> !tup_preserve |>

       Either a symbolic link or a copy of the source file will be created,
       depending on the OS and file system being used.

       Parsing a :-rule may be a little confusing at first. You may find it
       easy to think of the Tupfile as a shell script with additional
       input/output annotations for the commands. As an example, consider this

       WARNINGS += -W
       WARNINGS += -Wall
       CFLAGS = $(WARNINGS) -O2
       CFLAGS_foo.c = -DFOO
       : |> echo '#define BAR 3' > %o |> foo.h
       : foreach *.c | foo.h |> gcc -c %f -o %o $(CFLAGS) $(CFLAGS_%f) |> %B.o
       : *.o |> gcc %f -o %o |> program

       Tup begins parsing this Tupfile with an empty $-variable set. The first
       "WARNINGS += -W" line will set the WARNINGS variable to "-W". The
       second line will append, so WARNINGS will be set to "-W -Wall". The
       third line references this value, so CFLAGS will now equal "-W -Wall
       -O2". The fourth line sets a new variable, called CFLAGS_foo.c, and set
       it to -DFOO". The first rule will create a new node "foo.h" in the
       database, along with the corresponding command to create it. Note this
       file won't exist in the filesystem until the command is actually
       executed after all Tupfiles are parsed.
       The foreach :-rule will generate a command to compile each file. First
       tup will parse the input section, and use the glob operation on the
       database since a '*' is present. This glob matches foo.c and bar.c.
       Since it is a foreach rule, tup will run through the rule first using
       the input "foo.c", and again using the input "bar.c". The output
       pattern is parsed on each pass, followed by the command string.
       On the foo.c pass, the output pattern "%B.o" is parsed, which will
       equal "foo.o". Now the command string is parsed, replacing "foo.c" for
       "%f" and "foo.o" for "%o". The $-variables are then expanded, so
       $(CFLAGS) becomes "-W -Wall -O2", and $(CFLAGS_foo.c)" becomes "-DFOO".
       The final command string written to the database is "gcc -c foo.c -o
       foo.o -W -Wall -O2 -DFOO". An output link is written to the foo.o file,
       and input links are written from foo.c and foo.h (the order-only
       On the second pass through the foreach rule, the only difference is
       "bar.c" is the input. Therefore the output pattern becomes "bar.o", and
       the final command string becomes "gcc -c bar.c -o bar.o -W -Wall -O2 "
       since $(CFLAGS_bar.c) was unspecified.
       For more examples with corresponding DAGs, see
       Tup is a little bit different from other build systems. It uses a well-
       defined graph structure that is maintained in a separate database. A
       set of algorithms to operate on this graph were developed in order to
       handle cases such as modifying an existing file, creating or deleting
       files, changing command lines, etc. These algorithms are very efficient
       - in particular, for the case where a project is already built and one
       or more existing files are modified, tup is optimal among file-based
       build systems. For other cases, tup is at least very fast, but
       optimality has not been proved.
       The primary reason for the graph database is to allow the tup update
       algorithm to easily access the information it needs. As a very useful
       side-effect of the well-defined database structure, tup can determine
       when a generated file is no longer needed. What this means is there is
       no clean target. Nor is there a need to do a "fresh checkout" and build
       your software from scratch. Any number of iterations of updates always
       produces the same output as it would if everything was built anew.
       Should you find otherwise, you've likely found a bug in tup (not your
       Tupfiles), in which case you should notify the mailing list (see
       For more information on the theory behind tup, see

http://gittup.org/tup             2018/07/04                            tup(1)