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| author | Aki <please@ignore.pl> | 2023-03-26 18:07:18 +0200 |
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| committer | Aki <please@ignore.pl> | 2023-03-26 18:07:18 +0200 |
| commit | ea823149b20e9c3bec66369a5480353e48869279 (patch) | |
| tree | 7a85b34b790d416198e9932492ae1786b6139bb1 /how_to_create_templates_with_shell_cat_and_envsubst.html | |
| parent | 7d326b8524cfc4b6fb5a34d12143ccc5df20b28e (diff) | |
| download | ignore.pl-ea823149b20e9c3bec66369a5480353e48869279.zip ignore.pl-ea823149b20e9c3bec66369a5480353e48869279.tar.gz ignore.pl-ea823149b20e9c3bec66369a5480353e48869279.tar.bz2 | |
Rewrote fresh shell templating article
Diffstat (limited to 'how_to_create_templates_with_shell_cat_and_envsubst.html')
| -rw-r--r-- | how_to_create_templates_with_shell_cat_and_envsubst.html | 72 |
1 files changed, 0 insertions, 72 deletions
diff --git a/how_to_create_templates_with_shell_cat_and_envsubst.html b/how_to_create_templates_with_shell_cat_and_envsubst.html deleted file mode 100644 index 8eb730d..0000000 --- a/how_to_create_templates_with_shell_cat_and_envsubst.html +++ /dev/null @@ -1,72 +0,0 @@ -<!doctype html> -<html lang="en"> -<meta charset="utf-8"> -<meta name="viewport" content="width=device-width, initial-scale=1"> -<meta name="author" content="aki"> -<meta name="tags" content="tutorial, template, templating, cat, shell, envsubst"> -<link rel="icon" type="image/png" href="favicon.png"> -<link rel="stylesheet" type="text/css" href="style.css"> - -<title>How to Create Templates With Shell, cat and envsubst</title> - -<nav><p><a href="https://ignore.pl">ignore.pl</a></p></nav> - -<article> -<h1>How to Create Templates With Shell, cat and envsubst</h1> -<p class="subtitle">Published on 2020-07-14 20:26:00+02:00 -<p>Now something trivial and fun. Creating templates of documents or configurations in shell. There are two reasons why -I considered doing that instead of using some more verbose utilities. First off, availability - I have POSIX compliant -shell pretty much everywhere I go. It's a big part of my usual environment and because of that I'm used to it. That's -the second reason - frequency I use it with. It's good to mention that it's one of more verbose utilities out there. -<p>Let's start with plain shell. I actually use this method to serve the blog posts via fcgiwrap. I use it with a single -file, but it can accept external files. However those files won't have their content expanded in any way. If you keep it -in a one script file then it's possible. Basically, I'm talking about <code>cat</code>:</p> -<pre> -#!/bin/sh -cat /dev/fd/3 $@ /dev/fd/4 3<<BEFORE 4<<AFTER -<!doctype html> -<html lang="en"> -BEFORE -<script src=""></script> -AFTER -</pre> -<img src="how_to_create_templates_with_shell_cat_and_envsubst-1.png" alt="actual cat"> -<p>What you see here is a combination of -<a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04">heredoc</a> and plain -redirection. It's done like this to avoid calling <code>cat</code> more than once. The script simply concatenates BEFORE -heredoc with any arguments passed to the script, and finally with AFTER heredoc. The output is similar to what you see -in source of this page. The template is trimmed for the sake of the example. -<p>Now, now. Heredoc can easily expand variables but if we were to <code>cat before.inl $@ after.inl</code> it wouldn't -work. For that I use -<code><a href="https://www.gnu.org/software/gettext/manual/html_node/envsubst-Invocation.html">envsubst</a></code>. -Consider file called <i>template.conf</i>: -<pre> -server { - listen 80; - server_name $DOMAIN$ALIASES; - root /srv/http/$DOMAIN/public; -} -</pre> -<p>It could be wrapped in cat and heredoc, but for me it's not desired. Let's say I want my configuration templates to -be exactly that not executable scripts. There are three different solutions that I've heard: <code>eval</code>, -<code>sed</code> and <code>envsubst</code>. <code>Eval</code> can lead to dangerous situations and minor problems with -whitespace. <code>Sed</code> is what I believe is the most typical and straight-forward solution. As for the last one, -it goes like this:</p> -<pre> -$ export DOMAIN=example.tld -$ export ALIASES=' www.example.tld' -$ envsubst '$DOMAIN$ALIASES' <template.conf -server { - listen 80; - server_name example.tld www.example.tld; - root /srv/http/example.tld/public; -} -</pre> -<p>First, you set the variables (if they are not yet there). Then call the <code>envsubst</code> with a single variable -and redirect the template file into it. This single variable is called <em>SHELL-FORMAT</em>. It restricts the variables -that will be substituted in the input. It's completely optional, but if you have some <code>$server_name</code> you -don't want to substitute, then it's kind of useful. It actually doesn't have any format, you just need to reference the -variables in it: <code>'$DOMAIN$ALIASES'</code>, <code>'$DOMAIN $ALIASES'</code>, and <code>'$DOMAIN,$ALIASES'</code> -all work the same. -</article> -<script src="https://stats.ignore.pl/track.js"></script> |