mirror of
https://github.com/Brandon-Rozek/website.git
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87 lines
2.3 KiB
Markdown
87 lines
2.3 KiB
Markdown
---
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title: "Run a command when a file in a directory changes"
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date: 2024-01-05T16:00:53-05:00
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draft: false
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tags: []
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math: false
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medium_enabled: false
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---
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When editing code or adding content to a HTML file for a website, it can be very useful to see the changes right away after you save the file. We'll show a lightweight way of accomplishing this task with `entr` and a bit of bash scripting.
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First if you don't already have it, install `entr`.
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```bash
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sudo dnf install entr
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```
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This terminal application works by monitoring files passed within standard in. Therefore, to run a `$command` if any file under some `$directory` changes run the following:
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```bash
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find $directory -type f | entr $command
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```
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An example can be running a build script if anything under the source folder changes:
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```bash
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find src -type f | entr ./build.sh
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```
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Now this doesn't capture files that get added to the directory. To do this, we need to get `entr` to monitor the parent folder for any changes. We can do this with the `-d` flag.
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From the man page:
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> **-d** Track the directories of regular files provided as input and exit if
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> a new file is added.
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Since `entr` exits when a file gets added with this flag, the [common solution](https://superuser.com/a/665208) on the internet is to wrap it in a `while` loop.
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```bash
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$ while sleep 0.1 ; do find $directory -type f | entr -d $command ; done
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```
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This solution works great as a one-liner, but it doesn't let me CTRL-C out when I'm finished. Therefore, I wrote a shell script that incorporates this solution while also adding a `trap`.
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```bash
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#!/bin/bash
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set -o nounset
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set -o pipefail
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show_usage() {
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echo "Usage: entr-dir [dir] [command]"
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exit 1
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}
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# Check argument count
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if [ "$#" -lt 2 ]; then
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show_usage
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fi
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# Make sure that the command entr exists
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if ! command -v entr > /dev/null ; then
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echo "entr not found. Exiting..."
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exit 1
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fi
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DIR="$1"; shift
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if [[ ! -d "$DIR" ]]; then
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echo "First argument must be a directory. Exiting..."
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exit 1
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fi
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# Allow for CTRL-C to exit script
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trap "exit 0;" SIGINT
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while sleep 0.1; do
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find "$DIR" -type f | entr -d "$@"
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done
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```
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I plopped this in `~/.local/bin/entr-dir`, gave it the `+x` permission, and now I can easily monitor and build projects when files get changed/added/deleted.
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```bash
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entr-dir src ./build.sh
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```
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