tldr/pages/common/envsubst.md

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# envsubst
> Substitutes shell format strings with environment variables in text.
> Strings to be replaced should be in either `${var}` or `$var` format.
- Replace environment variables in stdin and output to `stdout`:
`echo '{{$HOME}}' | envsubst`
- Replace environment variables in an input file and output to `stdout`:
`envsubst < {{path/to/input}}`
- Replace environment variables in an input file and output to a file:
`envsubst < {{path/to/input}} > {{path/to/output}}`
- Replace environment variables in input from a space-separated list:
`envsubst {{variables}} < {{path/to/input}}`