write-envdir

#!/bin/bash
# usage: write-envdir <envdir> [[var1 [var2 [var3 […]]]]
#
# Writes the current value for each environment variable name given into the
# directory <envdir>, one file per variable.  Creates <envdir> if it doesn't
# already exist.
#
# This was copied from the ncov-ingest repo:
# <https://github.com/nextstrain/ncov-ingest/blob/20b432624ad2c4bf24c85756bd04bae1e067bde8/bin/write-envdir>
#
set -eou pipefail

dir="${1:?no envdir path}"
shift

mkdir -pv "$dir"
cd "$dir"

for name in "$@"; do
    # We could use [[ -v "$name" ]] if we didn't care about ancient Bash on
    # macOS.  Since we kinda do—it's useful in dev for folks to be able to run
    # programs locally—use `declare | grep` instead.  This is imperfect: if
    # $name contains regex metachars they'll be interpreted when they shouldn't
    # be.  Ah well.  I don't expect that to actually happen.
    #
    # We don't use ${!name:+…} or ${!name:-} to detect set/unset because they
    # both treat declared-but-empty-string-valued variables as unset.  It's a
    # legitimate use case to want to set a env var to an empty string.
    #
    #   -trs, 22 May 2024
    if ! declare | grep -qE "^$name="; then
        echo "error: $name is not set" >&2
        exit 1
    fi
    echo "${!name}" > "$name"
    echo "Wrote $dir/$name"
done