Package management Last updated Mar 18, 2025

The standard package manager for OCaml is opam.

Instruction for configuring an opam switch is beyond the scope of this guide, but here are some common useful commands:

  • $ opam switch show - prints the name of the current switch

  • $ opam switch - shows all installed switches

  • $ opam list - shows all packages installed in the current switch

  • $ opam pin list - shows all "pinned" packages

  • $ opam config list - lists all general configuration settings

  • $ opam config list ounit2 - lists all configuration settings for package ounit2

  • $ opam var - same as opam config list

  • $ opam var bin - print the value of the bin var of the current switch

  • $ opam var --package <pkg> - prints all variables for package <pkg> as <pkg>:<var>

  • $ opam var <pkg>:<var> - prints value of variable for package, e.g.

    • $ opam var ounit2:version - prints version string of package ounit2

"opam var --package …​" may be very, very slow.

OPAM switch names commonly match the version string of the installed compiler, but this is not required; you can name your switches however you wish. In that case, here are some useful commands, using --switch <s> to pick out a switch:

  • $ opam list --switch myswitch - list packages installed for switch myswitch

  • $ opam config list --switch myswitch - prints variables for switch myswitch.

  • $ opam var --package ocaml --switch myswitch - prints variables for the ocaml package of switch myswitch

    • $ opam var ocaml:version --switch myswitch - prints version variable of the ocaml package of switch myswitch

    • $ opam var ocaml:depends --switch myswitch - prints depends variable (i.e. compiler build options) of the ocaml package of switch myswitch

  • $ opam var --package ocaml-base-compiler --switch myswitch - prints variables for the ocaml-base-compiler package of switch myswitch

Compiler versions are treated as (pseudo) packages. When you run $ opam switch you will see that the "compiler" column lists strings of form <pkgname>.<varname>; for example, ocaml-base-compiler.4.12.0. If you have installed a compiler with +options the string will look like ocaml-variants.4.14.0+options. Use the <pkgname> part to obtain information about the compiler, e.g. $ opam var --package ocaml-base-compiler:version --switch myswitch.
The ocaml-base-compiler variable is unreliable! Don’t use it unless it is listed in the output of $ opam config list --switch myswitch.

  • If you use emacs, you probably want to install merlin.

  • Locally installed (system) libraries. Some OPAM packages depend on locally installed resources. For example, package bignum depends on package zarith, which depends on a local installation of libgmp (usually in /usr/local).