[{"_1":2,"_169":-5,"_170":-5},"loaderData",{"_3":4,"_13":14,"_21":22,"_144":145},"root",{"_5":-5,"_6":-7,"_7":8,"_9":-7,"_10":11,"_12":-7},"currentUser","primaryEmail","siteVerification","6LeIxAcTAAAAAJcZVRqyHh71UMIEGNQ_MXjiZKhI","toast","enableDev",false,"incidentStatus","routes/_layout",{"_15":-5,"_16":17,"_18":17,"_19":11,"_20":11},"username","isAskGordonEnabled",true,"isUsingNewTemplate","showMinimalLanding","showHoneypotTrap","routes/_layout.r.$namespace.$reponame",{"_23":24,"_25":-5,"_26":11,"_27":11,"_28":29,"_30":31,"_32":-5,"_33":11,"_34":35,"_84":-5,"_85":86,"_135":-5,"_136":11,"_137":17,"_138":11,"_139":-5,"_140":11,"_141":-5,"_142":143},"canonicalUrl","https://hub.docker.com/r/mqsoh/watcherl/tags","mcpServer","canSeeDockerfile","canSeeAutobuilds","namespace","mqsoh","reponame","watcherl","cloudBuildSource","isAutobuildsAvailable","repo",{"_36":37,"_38":39,"_41":42,"_43":44,"_45":11,"_46":47,"_48":49,"_50":51,"_53":31,"_28":29,"_54":55,"_56":40,"_57":58,"_59":60,"_61":62,"_63":-5,"_64":58,"_65":66,"_67":11,"_68":29,"_69":70,"_75":17,"_76":77,"_81":29,"_82":83},"categories",[],"content_types",[40],"image","date_registered","2016-04-15T13:21:51.913796Z","description","An image to start an Erlang shell that automatically compiles and reloads modules.","is_private","last_updated","2017-01-09T01:44:11.120355Z","last_modified","2024-10-16T13:48:34.145251Z","media_types",[52],"application/vnd.docker.container.image.v1+json","name","pull_count",1247,"repository_type","star_count",0,"status",1,"status_description","active","source","collaborator_count","full_description","# Watcherl\n\nThis is a Docker image that will start an Erlang shell. It watches `src/` for\nchanges and recompiles them. It checks for changes in `ebin/` and reloads\nmodules.\n\nI'm using [`compile:file/2`](http://erlang.org/doc/man/compile.html#file-2).\nYou can specify compiler arguments in the environment variable\n`WATCHERL_COMPILER_OPTIONS`. The default value is `[verbose, report, {outdir,\n\"ebin\"}]`; if you define new options they override the default so I recommend\nadding to that list. For example, if you use eunit for testing and need do\ndefine the `TEST` macro:\n\n [verbose, report, {outdir, \"ebin\"}, {d, 'TEST'}]\n\nYou can augment the code path with the environment variable\n[ERL_LIBS](http://erlang.org/doc/man/code.html) but there's no code reloading.\n\nHere's the minimal `docker run` command you need to run.\n\n docker run --interactive --tty --rm --volume $(pwd):/workdir mqsoh/watcherl\n\nHere's one where I'm developing an application with dependencies in `deps/` and\nhave eunit tests.\n\n docker run --interactive --tty --rm --volume $(pwd):/workdir --env \"ERL_LIBS=$(find deps -type d -name ebin)\" --env \"WATCHERL_COMPILER_OPTIONS=[verbose, report, {outdir, \\\"ebin\\\"}, {d, 'TEST'}]\" mqsoh/watcherl\n\n\n\n# Outline of the Dockerfile\n\nI'm going to use `inotify-tools` to watch the `workdir`. It will send messages\nto a process in the shell that's started.\n\n\n###### file:Dockerfile\n # This file was generated from the README.md in the GitHub repository.\n FROM erlang:19.2\n\n <>\n <>\n <>\n\n\n\n# Install inotify-tools.\n\nThe official Erlang image is based on Debian Jessie; `inotify-tools` is in the\npackage manager.\n\n###### Install inotify-tools.\n RUN apt-get update \\\n && apt-get install -y inotify-tools \\\n && apt-get clean \\\n && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*\n\nThe `apt-get clean` and `rm ...` cleans up any unnecessary `apt` stuff. I saw\nthis suggested in an article, but I didn't save the link.\n\n\n\n# The Bash side.\n\nThe `WORKDIR /workdir` line is a convention I like to use in my images; I\nalways have a `--volume $(pwd):/workdir`. The script to start the shell will be\ninstalled in the image from `files/watcherl.sh`\n\n###### The Bash side.\n WORKDIR /workdir\n COPY files/watcherl.sh /usr/local/bin/watcherl.sh\n RUN chmod +x /usr/local/bin/watcherl.sh\n CMD [\"watcherl.sh\"]\n\nI can use `inotifywait` to be notified of changes in `src` and `ebin`.\n\n###### file:files/watcherl.sh\n #!/bin/bash\n # This file was generated from the README.md.\n\n inotifywait --monitor --event close_write,moved_to --format '%w%f' ebin src | while read file; do\n case $file in\n <>\n esac\n done &\n\n <>\n\nI've used inotifywait before, and I usually just use the `close_write` event to\nidentify changes to a file. However, it seems that the Erlang compiler's\nsequence of events is this:\n\n src/ OPEN foo.erl\n src/ ACCESS foo.erl\n src/ ACCESS foo.erl\n src/ CLOSE_NOWRITE,CLOSE foo.erl\n ebin/ CREATE foo.bea#\n ebin/ OPEN foo.bea#\n ebin/ MODIFY foo.bea#\n ebin/ CLOSE_WRITE,CLOSE foo.bea#\n ebin/ MOVED_FROM foo.bea#\n ebin/ MOVED_TO foo.beam\n\nIt initially writes to `foo.bea#` and them moves that to the `.beam` extension.\nThat's why `moved_to` is included in the list of events.\n\n### Sending Messages to the Shell\n\nWhen files are changed I need to send a message to the running shell. I'll\nenumerate those processes below, but first I have to be able to send a message\nto them! Here is [an example of sending a message between processes on the same\nnode][]. And here's my abbreviated example with a bash one-liner.\n\n erl -sname one\n > register(my_process, spawn(fun () -> receive Any -> io:format(\"Got: ~w~n\", [Any]) end end)).\n true\n\nAnd from the bash prompt:\n\n $ erl -noshell -sname two -eval '{my_process, list_to_atom(\"one@\" ++ net_adm:localhost())} ! from_the_shell' -s init stop\n\nIn the Erlang shell, you'll see:\n\n Got: from_the_shell\n\nThe `-sname ` puts Erlang in distributed mode and lets me send a message.\nSo, all I need to do is pick names for the process that will compile and reload\nfiles. I'll call them `watcherl_compiler` and `watcherl_reloader`.\n\nRemember, these following sections are inside the `case` statement in `watcherl.sh`.\n\n###### Handle changes.\n *.erl)\n erlang_code=\"{watcherl_compiler, list_to_atom(\\\"watcherl@\\\" ++ net_adm:localhost())} ! \\\"$file\\\"\"\n erl -noshell -sname \"watcherl_sh_src_$RANDOM\" -eval \"$erlang_code\" -s init stop &\n ;;\n\n *.beam)\n module_name=$(basename \"$file\" .beam)\n erlang_code=\"{watcherl_reloader, list_to_atom(\\\"watcherl@\\\" ++ net_adm:localhost())} ! \\\"$module_name\\\"\"\n\n erl -noshell -sname \"watcherl_sh_beam_$RANDOM\" -eval \"$erlang_code\" -s init stop &\n ;;\n\nThe `erl ...` calls need to be backgrounded because, in my experience, it will\nblock the processing of other inotifywait events if you don't.\n\nI called the shell `watcherl` above (the `watcherl@` parts), so I need to call\nit that when I start the shell. Also, I'm going to start these processes in the\n`.erlang`, but I want the image to be useful in other ways so I'll set up a\ncommand line flag to turn them on.\n\n###### Start the shell.\n erl -watcherl_on -sname watcherl -pa ebin\n\n\n\n# The Erlang side.\n\n[Erlang supports shell configuration in a `.erlang` file.][] The commands in\nthis file are run in the shell as if a user had typed them (in the same\ncontext). You can define helper functions here!\n\nI need to add the `.erlang` to the Docker image.\n\n###### The Erlang side.\n COPY files/dot_erlang /root/.erlang\n\nThe file itself needs to start the compiler and reloader processes if they're\nturned on from the command line.\n\n###### file:files/dot_erlang\n % This file was generated from the README.md.\n case init:get_argument(watcherl_on) of\n {ok, _} ->\n io:format(\"~nwatcherl: Starting the compiler and BEAM reloader.~n\"),\n <>\n ,\n <>\n ,\n <>\n ;\n _ -> ok\n end.\n\nThe dangling `,` and `;` mean that I can define those code sections in the same\nway, without terminating the term, in the following sections.\n\nI'd like to be able to override the compiler options with an environment\nvariable. It's not straight forward. `term_to_binary` and `binary_to_term` uses\na binary format and I couldn't figure out how to pass them a bitstring. I found\n[a solution on a mailing\nlist](http://erlang.org/pipermail/erlang-questions/2007-August/028652.html)\nthat is a bit more convoluted. It makes sense, though. For the sake of\narchiving, here's the example from that post.\n\n > TupleListStr = \"[{a, b, c}, {d, e}]\".\n \"[{a, b, c}, {d, e}]\"\n > {ok, TermTokens, _EndLine} = erl_scan:string(TupleListStr ++ \".\").\n {ok,[{'[',1},\n {'{',1},\n {atom,1,a},\n {',',1},\n {atom,1,b},\n {',',1},\n {atom,1,c},\n {'}',1},\n {',',1},\n {'{',1},\n {atom,1,d},\n {',',1},\n {atom,1,e},\n {'}',1},\n {']',1},\n {dot,1}],\n 1}\n > {ok, Exprs} = erl_parse:parse_exprs(TermTokens).\n {ok,[{cons,1,\n {tuple,1,[{atom,1,a},{atom,1,b},{atom,1,c}]},\n {cons,1,{tuple,1,[{atom,1,d},{atom,1,e}]},{nil,1}}}]}\n > {value, TupleList, _NewBindings} = erl_eval:exprs(Exprs, []).\n {value,[{a,b,c},{d,e}],[]}\n > TupleList.\n [{a,b,c},{d,e}]\n\n###### Start the compiler.\n Compiler_options = begin\n Given_options = os:getenv(\"WATCHERL_COMPILER_OPTIONS\", \"[verbose, report, {outdir, \\\"ebin\\\"}]\") ++ \".\",\n {ok, Tokens, _End_location} = erl_scan:string(Given_options),\n {ok, Expressions} = erl_parse:parse_exprs(Tokens),\n {value, Value, _New_bindings} = erl_eval:exprs(Expressions, []),\n Value\n end,\n register(watcherl_compiler, spawn(fun F() ->\n receive\n File_name ->\n case compile:file(File_name, Compiler_options) of\n error ->\n io:format(\"~nwatcherl: Unspecified error compiling: ~s~n\", [File_name]);\n {error, Errors, Warnings} ->\n io:format(\"~nwatcherl: Failed compiling ~s with errors (~p) and warnings (~p).~n\", [File_name, Errors, Warnings]);\n _ ->\n io:format(\"~nwatcherl: Compiled: ~s~n\", [File_name])\n end\n end,\n F()\n end))\n\n###### Start the BEAM reloader.\n register(watcherl_reloader, spawn(fun F() ->\n receive\n Module_name ->\n io:format(\"~nwatcherl: Reloading: ~s~n\", [Module_name]),\n Module = list_to_atom(Module_name),\n code:purge(Module),\n code:load_file(Module)\n end,\n F()\n end))\n\nTo avoid unnecessary bootstrapping of new projects, I'll automatically compile\nany files in `src/` when the shell starts.\n\n###### Compile initial files.\n case file:list_dir(\"src\") of\n {ok, Initial_files} ->\n lists:foreach(fun (Filename) ->\n watcherl_compiler ! \"src/\" ++ Filename\n end,\n Initial_files);\n _ -> ok\n end\n\n\n\n[Erlang supports shell configuration in a `.erlang` file.]: http://erlang.org/doc/man/erl.html#id179026\n[an example of sending a message between processes on the same node]: http://stackoverflow.com/a/16913797/8710\n[ERL_LIBS]: http://erlang.org/doc/man/code.html\n","has_starred","hub_user","immutable_tags_settings",{"_71":11,"_72":73},"enabled","rules",[74],".*","is_automated","permissions",{"_78":17,"_79":11,"_80":11},"read","write","admin","user","storage_size",627383609,"orgData","recentTags",[87,125],{"_88":40,"_89":90,"_91":92,"_93":94,"_95":96,"_46":114,"_115":90,"_116":29,"_117":52,"_53":118,"_119":120,"_121":105,"_122":114,"_123":62,"_124":17},"content_type","creator",366554,"full_size",325812838,"id",2673045,"images",[97],{"_98":99,"_100":101,"_102":103,"_104":105,"_106":107,"_108":109,"_110":103,"_111":-5,"_112":92,"_59":62,"_113":-5},"architecture","amd64","digest","sha256:c4bdf28b416a27e1ebf42947dbd6e55fe0e6860dc0287b97edc7b73c0c6a2b38","features","","last_pulled","2026-09-22T07:18:32.424719747Z","last_pushed","2017-01-09T01:44:11Z","os","linux","os_features","os_version","size","variant","2017-01-09T01:44:10.797239Z","last_updater","last_updater_username","media_type","latest","repository",637852,"tag_last_pulled","tag_last_pushed","tag_status","v2",{"_88":40,"_89":90,"_91":126,"_93":127,"_95":128,"_46":133,"_115":90,"_116":29,"_117":52,"_53":134,"_119":120,"_121":131,"_122":133,"_123":62,"_124":17},325812508,7065479,[129],{"_98":99,"_100":130,"_102":103,"_104":131,"_106":132,"_108":109,"_110":103,"_111":-5,"_112":126,"_59":62,"_113":-5},"sha256:8e70f279acaa0e33afd03b039ce6c8ca418ce79e77875bbf94697361c6d9703c","2026-09-06T20:11:05.501533393Z","2016-12-24T03:24:09Z","2016-12-24T03:24:08.172963Z","19.2","sbxKitMetadata","isPotentialSpam","isHubSbxKitsEnabled","showSbxLogoOverride","sbxTrademarkText","displaySecurityMetadata","tagAttestations","tagsHaveAttestations",[],"routes/_layout.r.$namespace.$reponame.tags",{"_34":146,"_153":154,"_142":167,"_168":11},{"_36":147,"_38":148,"_41":42,"_43":44,"_45":11,"_46":47,"_48":49,"_50":149,"_53":31,"_28":29,"_54":55,"_56":40,"_57":58,"_59":60,"_61":62,"_63":-5,"_64":58,"_65":66,"_67":11,"_68":29,"_69":150,"_75":17,"_76":152,"_81":29,"_82":83},[],[40],[52],{"_71":11,"_72":151},[74],{"_78":17,"_79":11,"_80":11},"tags",{"_155":156,"_157":-5,"_158":-5,"_159":160},"count",2,"next","previous","results",[161,164],{"_88":40,"_89":90,"_91":92,"_93":94,"_95":162,"_46":114,"_115":90,"_116":29,"_117":52,"_53":118,"_119":120,"_121":105,"_122":114,"_123":62,"_124":17},[163],{"_98":99,"_100":101,"_102":103,"_104":105,"_106":107,"_108":109,"_110":103,"_111":-5,"_112":92,"_59":62,"_113":-5},{"_88":40,"_89":90,"_91":126,"_93":127,"_95":165,"_46":133,"_115":90,"_116":29,"_117":52,"_53":134,"_119":120,"_121":131,"_122":133,"_123":62,"_124":17},[166],{"_98":99,"_100":130,"_102":103,"_104":131,"_106":132,"_108":109,"_110":103,"_111":-5,"_112":126,"_59":62,"_113":-5},[],"canDeleteTags","actionData","errors"]

mqsoh/watcherl

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