Envsubst: Difference between revisions
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This page was last edited on 30 December 2021, at 01:32.
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<code>envsubst</code>, short for '''env'''ironment '''subst'''itution, makes it easy to substitute environment variables in a text file. This is a simple way to template files. | <code>envsubst</code>, short for '''env'''ironment '''subst'''itution, makes it easy to substitute environment variables in a text file. This is a simple way to template files. | ||
== Usage == | ==Usage== | ||
<code>envsubst</code> can replace variables in the form of <code>${VAR}</code> and <code>$VAR</code> with the value defined as an environment variable. The template file is piped to <code>envsubst</code>. | <code>envsubst</code> can replace variables in the form of <code>${VAR}</code> and <code>$VAR</code> with the value defined as an environment variable. The template file is piped to <code>envsubst</code>. | ||
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| lang = bash | | lang = bash | ||
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Latest revision as of 01:32, 30 December 2021
envsubst, short for environment substitution, makes it easy to substitute environment variables in a text file. This is a simple way to template files.
Usage
envsubst can replace variables in the form of ${VAR} and $VAR with the value defined as an environment variable. The template file is piped to envsubst.
A simple example with one variable:
$ export FirstName=leo
$ echo "hello ${FirstName}" | envsubst
hello leo
To save the generated output, simply redirect it to a file.
$ export FirstName=leo
$ echo "hello ${FirstName}" | envsubst > hello.txt
While envsubst isn't capable of supporting more advanced shell features such as ${VAR:-default_value}, you can still make use of it inside a shell script.
#!/bin/bash
## If no argument is passed, FirstName will be set to 'stranger'
FirstName="${1:-stranger}"
echo "Hello there, $FirstName" | envsubst