DUNE-EXEC(1)

📦
version 3.24.1 · 15 versions
, in ubuntu stonking

💖 dune-exec — the dune exec glow-up guide 💖

okay bestie, sit down, hydrate, and let me tell you about dune-exec from the Dune Manual. This is the one where you get to run your stuff in basically the same environment as if you'd actually installed it. iconic behaviour honestly. 🎀

✨ NAME ✨

dune-exec — run a command in an environment that's ~basically~ the same as if an installation had actually gone down. no cap.

🌸 SYNOPSIS 🌸

dune exec [OPTION]… PROG [ARGS]…

🦋 DESCRIPTION 🦋

so here's the tea: dune exec -- COMMAND should behave exactly like if you did this whole ritual:

$ dune install
$ COMMAND

like, same energy, same outcome. fr fr.

and specifically? if you run dune exec ocaml, you get access to all the libraries defined in your workspace using your usual directives (think #require and friends). yes bestie, it just works. 💅

now, the path girlies need to pay attention:

  • When a leading / is present in the command (absolute path), then the path is interpreted as an absolute path.
  • When a / is present at any other position (relative path), then the path is interpreted as relative to the build context + current working directory (or the value of --root when you run it outside of the project root).

it's giving "know where you are before you run things." 🧚

👑 OPTIONS 👑

okay this is the long part, but every single one matters, so we're doing all of them. no skipping. periodt.

  • --action-stderr-on-success=VAL — literally the same as --action-stdout-on-success except it's for standard error instead of standard output. and if you're in a big ol' mono-repo, the slay combo is --action-stdout-on-success=swallow --action-stderr-on-success=must-be-empty. that combo guarantees a successful build has a "clean" empty output. chef's kiss. ✨
  • --action-stdout-on-success=VAL — this one controls how Dune deals with the standard output of actions when they ~succeed~. the possible values are:
    • print — just print it to Dune's output
    • swallow — completely ignore it
    • must-be-empty — enforce that the action printed nothing. with must-be-empty, Dune will consider the action failed if it printed anything to its standard output. 😭

the default is print.

  • --build-info — show build information. simple. cute. useful.
  • --context=CONTEXT (absent=default) — run the command in this build context.
  • --display-separate-messages — separate error messages with a blank line. breathing room for your errors, we love to see it.
  • --error-reporting=VAL (absent=deterministic) — controls when build errors get reported. the options:
    • early — reports errors as soon as they are discovered
    • deterministic — reports errors at the end of the build, in a deterministic order
    • twice — reports each error twice: once as soon as it's discovered, and then again at the end of the build, in a deterministic order
  • -f, --force — force actions associated to aliases to be re-executed even if their dependencies haven't changed. pushing through regardless, respect. 💪
  • --file-watcher=VAL (absent=automatic) — the mechanism to detect changes in the source. Automatic makes dune run an external program to detect changes. Manual means you notify dune that files have changed manually. you're in charge, bestie.
  • --no-build — don't rebuild target before executing. straight to the good part.
  • --passive-watch-mode — similar to [--watch], but it only starts a build when instructed externally by an RPC. it waits for the signal like a good student. 🫶
  • --sandbox=VAL (absent DUNE_SANDBOX env) — set sandboxing mode. some actions require a certain sandboxing mode, so they will ignore this setting. the allowed values are: none, symlink, copy, hardlink.
  • --stop-on-first-error — stop the build as soon as an error is encountered. no dragging it out.
  • -w, --watch — instead of terminating the build after completion, it waits continuously for file changes. she's committed. 👀
  • --wait-for-filesystem-clock — Dune digests file contents for better incrementality, and these digests are themselves cached. in some cases, Dune needs to drop some digest cache entries in order for things to be reliable. this option makes Dune wait for the file system clock to advance, so it doesn't need to drop anything. you should probably not care about this option; it is mostly useful for Dune developers to make Dune tests of the digest cache more reproducible. (iykyk, if you're not a Dune dev, this is not your problem, bestie. 😌)

🌈 COMMON OPTIONS 🌈

these ones are common to all commands, so they show up everywhere like that one friend who's at every party. 💜

  • --always-show-command-line — always show the full command lines of programs executed by dune.
  • --auto-promote — automatically promote files. this is similar to running dune promote after the build.
  • --build-dir=FILE (absent DUNE_BUILD_DIR env) — specified build directory. _build if unspecified.
  • --cache=VAL (absent DUNE_CACHE env) — enable or disable Dune cache. one of disabled, enabled-except-user-rules or enabled. default is enabled-except-user-rules.
  • --cache-check-probability=VAL (absent DUNE_CACHE_CHECK_PROBABILITY env) — check build reproducibility by re-executing randomly chosen rules and comparing their results with those stored in Dune cache. 👀
note: by increasing the probability of such checks you slow down the build. the default probability is zero, i.e. no rules are checked.
  • --cache-storage-mode=VAL (absent DUNE_CACHE_STORAGE_MODE env) — Dune cache storage mode. one of auto, hardlink or copy. default is hardlink.
  • --config-file=FILE — load this configuration file instead of the default one.
  • --debug-backtraces — always print exception backtraces. the receipts, forever.
  • --debug-dependency-path — in case of error, print the dependency path from the targets on the command line to the rule that failed. detective mode. 🔍
  • --debug-package-logs (absent DUNE_DEBUG_PACKAGE_LOGS env) — always print the standard logs when building packages.
  • --default-target=TARGET (absent=@@default) — set the default target that is used when none is specified to dune build.
  • --diff-command=VAL (absent DUNE_DIFF_COMMAND env) — shell command to use to diff files. use - to disable printing the diff.
  • --disable-promotion (absent DUNE_DISABLE_PROMOTION env) — disable all promotion rules.
  • --display=MODE — control the display mode of Dune. see dune-config(5) for more details. valid values for this option are progress, verbose, short, quiet or tui.
  • --dump-gc-stats=FILE — dump the garbage collector stats to a file after the build is complete. garbage collection data?? we love an informed queen. 🗑️✨
  • --help[=FMT] (default=auto) — show this help in format FMT. the value FMT must be one of auto, pager, groff or plain. with auto, the format is pager or plain whenever the TERM env var is dumb or undefined.
  • --ignore-promoted-rules — ignore rules with (mode promote), except ones with (only ...). the variable %{ignoring_promoted_rules} in dune files reflects whether this option was passed or not.
  • --instrument-with=BACKENDS (absent DUNE_INSTRUMENT_WITH env) — enable instrumentation by BACKENDS. BACKENDS is a comma-separated list of library names, each one of which must declare an instrumentation backend.
  • -j JOBS (absent DUNE_JOBS env) — run no more than JOBS commands simultaneously. JOBS must be a positive integer or auto to auto-detect the number of cores (the default).
  • --no-buffer — do not buffer the output of commands executed by dune. by default dune buffers the output of subcommands, in order to prevent interleaving when multiple commands are executed in parallel. however, this can be an issue when debugging long running tests. with --no-buffer, commands have direct access to the terminal. note that as a result their output won't be captured in the log file. you should use this option in conjunction with -j 1, to avoid interleaving. additionally you should use --verbose as well, to make sure that commands are printed before they are being executed.
  • --no-config — do not load the configuration file.
  • --no-print-directory — suppress "Entering directory" messages.
  • --only-packages=PACKAGES — ignore stanzas referring to a package that is not in PACKAGES. PACKAGES is a comma-separated list of package names. note that this has the same effect as deleting the relevant stanzas from dune files. it is mostly meant for releases. during development, it is likely that what you want instead is to build a particular <package>.install target.
  • -p PACKAGES, --for-release-of-packages=PACKAGES (required) — shorthand for --release --pkg=disabled --only-packages PACKAGE. you must use this option in your <package>.opam files, in order to build only what's necessary when your project contains multiple packages, as well as getting reproducible builds. mandatory, bestie. 👑
  • --pkg=VAL — enable or disable package management. the default behaviour depends on whether a lock directory exists.
  • --profile=VAL (absent DUNE_PROFILE env) — select the build profile, for instance dev or release. the default is dev.
  • --promote-install-files[=VAL] (default=true) — promote any generated <package>.install files to the source tree.
  • --release — put dune into a reproducible release mode. shorthand for --root . --ignore-promoted-rules --no-config --profile release --always-show-command-line --promote-install-files --require-dune-project-file --default-target @install. you should use this option for release builds. for instance, you must use this option in your <package>.opam files. except if you already use -p, as -p implies this option.
  • --require-dune-project-file[=VAL] (default=true) — fail if a dune-project file is missing.
  • --root=DIR (absent DUNE_ROOT env) — use this directory as workspace root instead of guessing it. note that this option doesn't change the interpretation of targets given on the command line. it is only intended for scripts.
  • --store-orig-source-dir (absent DUNE_STORE_ORIG_SOURCE_DIR env) — store original source location in dune-package metadata.
  • --target-exec=TOOLCHAIN=CMD (absent DUNE_TARGET_EXEC env) — wrapper command for running target binaries when cross-compiling. format: TOOLCHAIN=CMD (e.g., 'windows=wine').
  • --terminal-persistence=MODE — change how the log of build results are displayed to the console between rebuilds while in --watch mode. supported modes: preserve, clear-on-rebuild, clear-on-rebuild-and-flush-history.
  • --trace-file=FILE — output trace data in catapult format (compatible with chrome://tracing).
  • --verbose — same as --display verbose.
  • --version — show version information.
  • --watch-exclusions=REGEX — adds a POSIX regular expression that will exclude matching directories from dune build --watch. the option --watch-exclusions can be repeated to add multiple exclusions. semicolons can be also used as a separator. if no exclusions are provided, then a standard set of exclusions is used; however, if one or more --watch-exclusions are used, none of the standard exclusions are used. the standard exclusions are:
^_opam /_opam ^_esy /_esy ^\.#.* /\.#.* ~$ ^#[^#]*#$ /#[^#]*#$ ^4913$ /4913$ /.git /.hg :/windows
  • --workspace=FILE (absent DUNE_WORKSPACE env) — use this specific workspace file instead of looking it up.
  • -x VAL (absent DUNE_CROSS_TARGET env) — cross-compile using this toolchain.

🎀 MORE HELP 🎀

use dune COMMAND --help for help on a single command. like, if you want the deep lore on just one command, that's your girl. 💖

💀 EXIT STATUS 💀

so when dune exec finishes, here's the vibe check on what it hands back to you:

  • 0 — it worked bestie!! success, slay, everything ate ✨
  • 1 — okay so something went wrong, an error happened 😭
  • 130 — it got interrupted by a signal 🙈 (yes this is the classic "someone hit Ctrl+C" number)

🌈 ENVIRONMENT 🌈

these env vars are the little backstage crew that changes how exec behaves. know them, love them 👑

  • DUNE_BUILD_DIR — tells Dune which build directory to use. if you don't say anything it's _build, periodt.
  • DUNE_CACHE — turns the Dune cache on or off. pick one of disabled, enabled-except-user-rules, or enabled. the default is enabled-except-user-rules 💅
  • DUNE_CACHE_CHECK_PROBABILITY — this one checks whether your builds are reproducible by re-running randomly chosen rules and comparing the results to what's stored in the Dune cache. > ⚠️ heads up bestie: cranking up this probability slows your build down. the default probability is zero, meaning literally no rules get checked.
  • DUNE_CACHE_STORAGE_MODE — how the Dune cache stores stuff. pick one of auto, hardlink, or copy. default is hardlink ✨
  • DUNE_CROSS_TARGET — cross-compile using this toolchain.
  • DUNE_DEBUG_PACKAGE_LOGS — always prints the standard logs when building packages. no crumbs hidden 🍓
  • DUNE_DIFF_COMMAND — the shell command used to diff files. use - to disable printing the diff entirely.
  • DUNE_DISABLE_PROMOTION — disables all promotion rules, every single one 🚫
  • DUNE_INSTRUMENT_WITH — enables instrumentation by BACKENDS. BACKENDS is a comma-separated list of library names, and every single one of them has to declare an instrumentation backend. no backend, no dice.
  • DUNE_JOBS — run no more than JOBS commands at the same time. JOBS has to be a positive integer, or auto to auto-detect the number of cores (which is the default, and honestly a very good default 👑).
  • DUNE_PROFILE — the build profile. it's dev if unspecified, or release if -p is set.
  • DUNE_ROOT — use this directory as the workspace root instead of letting Dune guess. > ngl this one's a little special: it doesn't change how targets given on the command line are interpreted. it is only intended for scripts. iykyk.
  • DUNE_SANDBOX — the sandboxing mode to use by default. (peep --sandbox for the details 🫶)
  • DUNE_STORE_ORIG_SOURCE_DIR — stores the original source location inside the dune-package metadata.
  • DUNE_TARGET_EXEC — a wrapper command for running target binaries when you're cross-compiling. format: TOOLCHAIN=CMD (like, for example, 'windows=wine').
  • DUNE_WORKSPACE — use this specific workspace file instead of looking one up.

🐛 BUGS 🐛

found something cursed? check the bug reports at https://github.com/ocaml/dune/issues — the devs wanna hear it fr fr

👀 SEE ALSO 👀

  • dune(1) — the main character, go read it

🌸 EXAMPLES 🌸

  1. run the executable named my_exec:
dune exec my_exec
  1. run the executable defined in foo.ml with the argument arg:
dune exec -- ./foo.exe arg

and that's the whole page bestie, you made it to the end 🎀 this was Dune 3.24.1, page DUNE-EXEC(1), so go forth and dune exec your little heart out. obsessed with you. bye!! 💖✨🦋

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