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https://github.com/cespare/reflex

Run a command when files change
https://github.com/cespare/reflex

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Run a command when files change

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README 

        
# Reflex



Reflex is a small tool to watch a directory and rerun a command when certain

files change. It's great for automatically running compile/lint/test tasks and

for reloading your application when the code changes.



## A simple example



    # Rerun make whenever a .c file changes

    reflex -r '\.c$' make



## Installation



You can download binaries from the

[Releases page](https://github.com/cespare/reflex/releases).



To compile from source, you'll need Go 1.13+ installed.



If you have Go 1.16 or later, you can download and install the latest module

version directly with



    go install github.com/cespare/reflex@latest



Reflex is only tested on Linux and macOS.



## Usage



The following is given by running `reflex -h`:



```

Usage: reflex [OPTIONS] [COMMAND]



COMMAND is any command you'd like to run. Any instance of {} will be replaced

with the filename of the changed file. (The symbol may be changed with the

--substitute flag.)



OPTIONS are given below:

      --all=false:

            Include normally ignored files (VCS and editor special files).

  -c, --config="":

            A configuration file that describes how to run reflex

            (or '-' to read the configuration from stdin).

  -d, --decoration="plain":

            How to decorate command output. Choices: none, plain, fancy.

  -g, --glob=[]:

            A shell glob expression to match filenames. (May be repeated.)

  -G, --inverse-glob=[]:

            A shell glob expression to exclude matching filenames.

            (May be repeated.)

  -R, --inverse-regex=[]:

            A regular expression to exclude matching filenames.

            (May be repeated.)

      --only-dirs=false:

            Only match directories (not files).

      --only-files=false:

            Only match files (not directories).

  -r, --regex=[]:

            A regular expression to match filenames. (May be repeated.)

  -e, --sequential=false:

            Don't run multiple commands at the same time.

  -t, --shutdown-timeout=500ms:

            Allow services this long to shut down.

  -s, --start-service=false:

            Indicates that the command is a long-running process to be

            restarted on matching changes.

      --substitute="{}":

            The substitution symbol that is replaced with the filename

            in a command.

  -v, --verbose=false:

            Verbose mode: print out more information about what reflex is doing.



Examples:



    # Print each .txt file if it changes

    $ reflex -r '\.txt$' echo {}



    # Run 'make' if any of the .c files in this directory change:

    $ reflex -g '*.c' make



    # Build and run a server; rebuild and restart when .java files change:

    $ reflex -r '\.java$' -s -- sh -c 'make && java bin/Server'

```



### Overview



Reflex watches file changes in the current working directory and re-runs the

command that you specify. The flags change what changes cause the command to be

rerun and other behavior.



### Patterns



You can specify files to match using either shell glob patterns (`-g`) or

regular expressions (`-r`). If you don't specify either, reflex will run your

command after any file changes. (Reflex ignores some common editor and version

control files; see Ignored files, below.)



You can specify inverse matches by using the `--inverse-glob` (`-G`) and

`--inverse-regex` (`-R`) flags.



If you specify multiple globs/regexes (e.g. `-r foo -r bar -R baz -G x/*/y`),

only files that match all patterns and none of the inverse patterns are

selected.



The shell glob syntax is described

[here](http://golang.org/pkg/path/filepath/#Match), while the regular expression

syntax is described [here](https://code.google.com/p/re2/wiki/Syntax).



The path that is matched against the glob or regular expression does not have a

leading `./`. For example, if there is a file `./foobar.txt` that changes, then

it will be matched by the regular expression `^foobar`. If the path is a

directory, it has a trailing `/`.



### --start-service



The `--start-service` flag (short version: `-s`) inverts the behavior of command

running: it runs the command when reflex starts and kills/restarts it each time

files change. This is expected to be used with an indefinitely-running command,

such as a server. You can use this flag to relaunch the server when the code is

changed.



### Substitution



Reflex provides a way for you to determine, inside your command, what file

changed. This is via a substitution symbol. The default is `{}`. Every instance

of the substitution symbol inside your command is replaced by the filename.



As a simple example, suppose you're writing Coffeescript and you wish to compile

the CS files to Javascript when they change. You can do this with:



    reflex -r '\.coffee$' -- coffee -c {}



In case you need to use `{}` for something else in your command, you can change

the substitution symbol with the `--substitute` flag.



### Configuration file



What if you want to run many watches at once? For example, when writing web

applications I often want to rebuild/rerun the server when my code changes, but

also build SCSS and Coffeescript when those change as well. Instead of running

multiple reflex instances, which is cumbersome (and inefficient), you can give

reflex a configuration file.



The configuration file syntax is simple: each line is a command, and each

command is composed of flags and arguments -- just like calling reflex but

without the initial `reflex`. Lines that start with `#` are ignored. Commands

can span multiple lines if they're \\-continued, or include multi-line strings.

Here's an example:



    # Rebuild SCSS when it changes

    -r '\.scss$' -- \

       sh -c 'sass {} `basename {} .scss`.css'



    # Restart server when ruby code changes

    -sr '\.rb$' -- \

        ./bin/run_server.sh



If you want to change the configuration file and have reflex reload it on the

fly, you can run reflex inside reflex:



    reflex -s -g reflex.conf -- reflex -c reflex.conf



This tells reflex to run another reflex process as a service that's restarted

whenever `reflex.conf` changes.



### --sequential



When using a config file to run multiple simultaneous commands, reflex will run

them at the same time (if appropriate). That is, a particular command can only

be run once a previous run of that command finishes, but two different commands

may run at the same time. This is usually what you want (for speed).



As a concrete example, consider this config file:



    -- sh -c 'for i in `seq 1 5`; do sleep 0.1; echo first; done'

    -- sh -c 'for i in `seq 1 5`; do sleep 0.1; echo second; done'



When this runs, you'll see something like this:



    [01] second

    [00] first

    [01] second

    [00] first

    [00] first

    [01] second

    [01] second

    [00] first

    [01] second

    [00] first



Note that the output is interleaved. (Reflex does ensure that each line of

output is not interleaved with a different line.) If, for some reason, you need

to ensure that your commands don't run at the same time, you can do this with

the `--sequential` (`-e`) flag. Then the output would look like (for example):



    [01] second

    [01] second

    [01] second

    [01] second

    [01] second

    [00] first

    [00] first

    [00] first

    [00] first

    [00] first



### Decoration



By default, each line of output from your command is prefixed with something

like `[00]`, which is simply an id that reflex assigns to each command. You can

use `--decoration` (`-d`) to change this output: `--decoration=none` will print

the output as is; `--decoration=fancy` will color each line differently

depending on which command it is, making it easier to distinguish the output.



### Ignored files



Reflex ignores a variety of version control and editor metadata files by

default. If you wish for these to be included, you can provide reflex with the

`--all` flag.



You can see a list of regular expressions that match the files that reflex

ignores by default

[here](https://github.com/cespare/reflex/blob/master/defaultexclude.go#L5).



## Notes and Tips



If you don't use `-r` or `-g`, reflex will match every file.



Reflex only considers file creation and modification changes. It does not report

attribute changes nor deletions.



For ignoring directories, it's easiest to use a regular expression: `-R '^dir/'`.



Many regex and glob characters are interpreted specially by various shells.

You'll generally want to minimize this effect by putting the regex and glob

patterns in single quotes.



If your command has options, you'll probably need to use `--` to separate the

reflex flags from your command flags. For example: `reflex -r '.*\.txt' -- ls

-l`.



If you're going to use shell things, you need to invoke a shell as a parent

process:



    reflex -- sh -c 'sleep 1 && echo {}'



If your command is running with sudo, you'll need a passwordless sudo, because

you cannot enter your password in through reflex.



It's not difficult to accidentally make an infinite loop with certain commands.

For example, consider this command: `reflex -r '\.txt' cp {} {}.bak`. If

`foo.txt` changes, then this will create `foo.txt.bak`, `foo.txt.bak.bak`, and

so forth, because the regex `\.txt` matches each file. Reflex doesn't have any

kind of infinite loop detection, so be careful with commands like `cp`.



The restart behavior works as follows: if your program is still running, reflex

sends it SIGINT; after 1 second if it's still alive, it gets SIGKILL. The new

process won't be started up until the old process is dead.



### Batching



Part of what reflex does is apply some heuristics to batch together file

changes. There are many reasons that files change on disk, and these changes

frequently come in large bursts. For instance, when you save a file in your

editor, it probably makes a tempfile and then copies it over the target, leading

to several different changes. Reflex hides this from you by batching some

changes together.



One thing to note, though, is that the the batching is a little different

depending on whether or not you have a substitution symbol in your command. If

you do not, then updates for different files that all match your pattern can be

batched together in a single update that only causes your command to be run

once.



If you are using a substitution symbol, however, each unique matching file will

be batched separately.



### Argument list splitting



When you give reflex a command from the commandline (i.e., not in a config

file), that command is split into pieces by whatever shell you happen to be

using. When reflex parses the config file, however, it must do that splitting

itself. For this purpose, it uses [this library](https://github.com/kballard/go-shellquote)

which attempts to match `sh`'s argument splitting rules.



This difference can lead to slightly different behavior when running commands

from a config file. If you're confused, it can help to use `--verbose` (`-v`)

which will print out each command as interpreted by reflex.



### Open file limits



Reflex currently must hold an open file descriptor for every directory it's

watching, recursively. If you run reflex at the top of a big directory tree, you

can easily run into file descriptor limits. You might see an error like this:



    open some/path: too many open files



There are several things you can do to get around this problem.



1. Run reflex in the most specific directory possible. Don't run

   `reflex -g path/to/project/*.c ...` from `$HOME`; instead run reflex in

   `path/to/project`.

2. Ignore large subdirectories. Reflex already ignores, for instance, `.git/`.

   If you have other large subdirectories, you can ignore those yourself:

   `reflex -R '^third_party/' ...` ignores everything under `third_party/` in

   your project directory.

3. Raise the fd limit using `ulimit` or some other tool. On some systems, this

   might default to a restrictively small value like 256.



See [issue #6](https://github.com/cespare/reflex/issues/6) for some more

background on this issue.



## The competition



* https://github.com/guard/guard

* https://github.com/alexch/rerun

* https://github.com/mynyml/watchr

* https://github.com/eaburns/Watch

* https://github.com/alloy/kicker

* https://github.com/eradman/entr



### Why you should use reflex instead



* Reflex has no dependencies. No need to install Ruby or anything like that.

* Reflex uses an appropriate file watching mechanism to watch for changes

  efficiently on your platform.

* Reflex gives your command the name of the file that changed.

* No DSL to learn -- just give it a shell command.

* No plugins.

* Not tied to any language, framework, workflow, or editor.



## Authors



* Benedikt Böhm ([hollow](https://github.com/hollow))

* Caleb Spare ([cespare](https://github.com/cespare))

* PJ Eby ([pjeby](https://github.com/pjeby))

* Rich Liebling ([rliebling](https://github.com/rliebling))

* Seth W. Klein ([sethwklein](https://github.com/sethwklein))

* Vincent Vanackere ([vanackere](https://github.com/vanackere))