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Discussion on: September 9th, 2021: What did you learn this week?

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vonheikemen profile image
Heiker • • Edited

I learned about envsubst. I wish I knew about this before. This utility can substitute environment variables in a string that come from stdin.

I don't have many use cases for this but I think it would be very useful in config files that I share across multiple machines.

Quick example. Somewhere in a github repo I have a file called .npmrc, which I copy to any new machine I get. Inside that file I have this.

prefix=/absolute/path/to/npm/packages
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I don't like it, I want to replace that absolute path with this.

prefix=$XDG_CONFIG_HOME/npm/packages
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So, what I can do is create a template file and then create .npmrc from that.

envsubst < ~/templates/npmrc > ~/.npmrc
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The result on linux should be this:

prefix=/home/user/.config/npm/packages
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And if I wanted, I think I could use curl to fetch the content of the file and then pipe it to envsubst. So technically I don't even need the template in my filesystem.

EDIT: Yes, curl works like a charm.

curl -s "https://raw.githubusercontent.com/<my-user>/<some-repo>/main/npmrc" \
  | envsubst > ~/.npmrc
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nickytonline profile image
Nick Taylor •

Nice!

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