Little bash script to generate shell.nix default.nix

mknix.sh

#!/usr/bin/env bash

usage () {
    echo "Usage: $(basename $0) [--direnv] [--shell] [--default] -p|--packages packages... [--test]"
    exit 0
}

error () {
    echo "Error: $1"
    exit 1
}

DIRENV=0
SHELL=0
DEFAULT=0
TEST=0
POSITIONAL=()
while [[ $# -gt 0 ]]
do
key="$1"

case $key in
    -h|--help)
    usage
    ;;
    --test)
    TEST=1
    shift
    ;;
    --test)
    TEST=1
    shift
    ;;
    -p|--packages)
    shift
    ;;
    --default)
    DEFAULT=1
    shift
    ;;
    --direnv)
    DIRENV=1
    shift
    ;;
    --shell)
    SHELL=1
    shift
    ;;
    *)    # unknown option
    POSITIONAL+=("$1") # save it in an array for later
    shift
    ;;
esac
done
set -- "${POSITIONAL[@]}" # restore positional parameters

[ ${#POSITIONAL[@]} = 0 ] && error "Provide one or more package names as arguments."


TMP="$(mktemp)"
cat >"$TMP" <<EOF
with (import <nixpkgs> {});
mkShell {
  buildInputs = [
    ${POSITIONAL[@]}
  ];
}
EOF

[ $DEFAULT = 1 ] && cp -i "$TMP" ./default.nix
[ $SHELL = 1 ] && cp -i "$TMP" ./shell.nix
[ $DEFAULT = 0 ] && [ $SHELL = 0 ] && cat "$TMP"
[ $DIRENV = 1 ] && echo use nix >> ./.envrc
rm "$TMP"

[ $TEST = 1 ] && exec nix-shell -p ${POSITIONAL[@]}