Overview

Go Watch: missing watch mode for the go command. It's invoked exactly like go, but also watches Go files and reruns on changes.

Currently requires Unix (MacOS, Linux, BSD). On Windows, runs under WSL.

TOC

• Overview
• Why
• Installation
• Usage
• Hotkeys
• Configuration
• Scripting
• Gotchas
• Watching Templates
• Alternatives
• License
• Misc

Why

Why not other runners, general-purpose watchers, etc:

• Has hotkeys, such as ctrl+r to restart!
• Go-specific, easy to remember.
• Ignores non-Go files by default.
• Better watcher: recursive, no delays, no polling; uses https://github.com/rjeczalik/notify.
• Silent by default.
• No garbage files.
• Can properly clear the terminal on restart.
• Does not leak subprocesses.
• Minimal dependencies.

Installation

Make sure you have Go installed, then run this:

go install github.com/mitranim/gow@latest

This should download the source and compile the executable into $GOPATH/bin/gow. Make sure $GOPATH/bin is in your $PATH so the shell can discover the gow command. For example, my ~/.profile contains this:

export GOPATH="$HOME/go"
export PATH="$GOPATH/bin:$PATH"

Alternatively, you can run the executable using the full path. At the time of writing, ~/go is the default $GOPATH for Go installations. Some systems may have a different one.

~/go/bin/gow

On MacOS, if installation fails with dylib-related errors, you may need to run xcode-select --install or install Xcode. This is caused by gow's dependencies, which depend on C. See #15.

Usage

The first argument to gow, after the flags, can be any Go subcommand: build, install, tool, you name it.

# Start and restart on change
gow run .

# Pass args to the program
gow run . arg0 arg1 ...

# Run subdirectory
gow run ./subdir

# Vet and re-vet on change; verbose mode is recommended
gow -v vet

# Clear terminal on restart
gow -c run .

# Specify file extension to watch
gow -e=go,mod,html run .

# Help
gow -h

Hotkeys

Supported control codes with commonly associated hotkeys. Exact keys may vary between terminal apps. For example, ^- in MacOS Terminal vs ^? in iTerm2.

3     ^C          Kill subprocess with SIGINT.
18    ^R          Kill subprocess with SIGTERM, restart.
20    ^T          Kill subprocess with SIGTERM.
28    ^\          Kill subprocess with SIGQUIT.
31    ^- or ^?    Print currently running command.
8     ^H          Print help.
127   ^H (MacOS)  Print help.

In slightly more technical terms, gow switches the terminal into raw mode, reads from stdin, interprets some ASCII control codes, and forwards the other input to the subprocess as-is. In raw mode, pressing one of these hotkeys causes a terminal to write the corresponding byte to stdin, which is then interpreted by gow. This can be disabled with -r=false.

Configuration

At present, gow does not support config files. All configuration is done through CLI flags. This is suitable for small, simple projects. Larger projects typically use a build tool such as Make, which is also sufficient for managing the configuration of gow. See the example makefile.

Scripting

gow invokes an arbitrary executable; by default it invokes go which should be installed globally. For some advanced use cases, you may need a custom script. For example, if you want gow to run go generate before any other go operation, create a local shell script go.sh:

touch go.sh
chmod +x go.sh

...with the following content:

#!/bin/sh

go generate &&
go $@

To invoke it, use -g when running gow:

gow -g=./go.sh -v -c run .

Alternatively, instead of creating script files, you can write recipes in a makefile; see Configuration and the example makefile.

Gotchas

By default, gow tries to switch the terminal into "raw mode"; see 1. This allows to support hotkeys, but causes issues in the cases listed below. To disable this, run gow with -r=false, which also disables hotkey support.

Gotcha: non-interactive environment

By default, gow expects to be a foreground process in an interactive terminal. When running gow as a background process, in Docker, or in any other non-interactive environment, you may see errors related to terminal state. Examples of such errors:

> unable to read terminal state
> inappropriate ioctl for device
> operation not supported by device

Gotcha: concurrent instances of gow in one terminal

There should be only one gow -r=true per terminal tab. When running multiple gow processes in one terminal tab, most should be gow -r=false. gow processes do not coordinate. If several are attempting to modify the terminal state (from cooked mode to raw mode, then restore), due to a race condition, they may end up "restoring" the wrong state, leaving the terminal in the raw mode at the end.

Watching Templates

Many Go programs, such as servers, include template files, and want to recompile those templates on change.

Easy but slow way: use gow -e.

gow -e=go,mod,html run .

This restarts your entire app on change to any .html file in the current directory or sub-directories. Beware: if the app also generates files with the same extensions, this could cause an infinite restart loop. Ignore any output directories with -i:

gow -e=go,mod,html -i=target run .

A smarter approach would be to watch the template files from inside the app and recompile them without restarting the entire app. This is out of scope for gow.

Finally, you can use a pure-Go rendering system such as github.com/mitranim/gax.

Alternatives

For general purpose file watching, consider these excellent tools:

• https://github.com/mattgreen/watchexec
• https://github.com/emcrisostomo/fswatch

License

https://unlicense.org

Misc

I'm receptive to suggestions. If this tool almost satisfies you but needs changes, open an issue or chat me up. Contacts: https://mitranim.com/#contacts