Initial

,

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+#!/bin/bash
+#
+# usage example:
+#   $ , yarn --help
+# This finds a derivation providing a bin/yarn, and runs it with `nix run`.
+# If there are multiple candidates, the user chooses one using `fzy`.
+set -euo pipefail
+
+if [[ $# -lt 1 ]]; then
+  >&2 echo "usage: , <program> [arguments]"
+  exit 1
+fi
+
+if [[ "$1" == "--install" ]] || [[ "$1" == "-i" ]]; then
+  install=1
+  shift
+else
+  install=""
+fi
+
+argv0=$1; shift
+
+case "${argv0}" in
+  @OVERLAY_PACKAGES@)
+    attr="${argv0}"
+    ;;
+  *)
+    attr="$(nix-locate --db "${NIX_INDEX_DB}" --top-level --minimal --at-root --whole-name "/bin/${argv0}")"
+    if [[ "$(echo "${attr}" | wc -l)" -ne 1 ]]; then
+      attr="$(echo "${attr}" | fzy)"
+    fi
+    ;;
+esac
+
+if [[ -z $attr ]]; then
+  >&2 echo "no match"
+  exit 1
+fi
+
+if [[ -n $install ]]; then
+  nix-env -iA "nixpkgs.${attr%%.*}"
+else
+  nix run "nixpkgs.${attr}" -c "${argv0}" "$@"
+fi

README.md

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+# ,
+
+Comma runs software without installing it.
+
+Basically it just wraps together `nix run` and `nix-index`. You stick a `,` in front of a command to
+run it from whatever location it happens to occupy in `nixpkgs` without really thinking about it.
+
+## Installation
+
+```bash
+nix-env -i -f .
+```
+
+## Usage
+
+```bash
+, cowsay neato
+```

default.nix

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+{ pkgs ? import <nixpkgs> { }
+
+, stdenv ? pkgs.stdenv
+, lib ? pkgs.lib
+, fetchurl ? pkgs.fetchurl
+, nix-index ? pkgs.nix-index
+, nix ? pkgs.nix
+, fzy ? pkgs.fzy
+, makeWrapper ? pkgs.makeWrapper
+, runCommand ? pkgs.runCommand
+
+# We use this to add matchers for stuff that's not in upstream nixpkgs, but is
+# in our own overlay. No fuzzy matching from multiple options here, it's just:
+# Was the command `, mything`? Run `nixpkgs.mything`.
+, overlayPackages ? []
+}:
+
+let
+
+  # nix-index takes a little while to run and the contents don't change
+  # meaningfully very often. This is generated by running `nix-index` and
+  # uploading `~/.cache/nix-index/files` to, well, anywhere.
+  indexCache = fetchurl {
+    url = "https://s3.amazonaws.com/burkelibbey/nix-index-files";
+    sha256 = "06p58f82wipd0a8wbc7j3l0p8iaxvdibgshmc9dbxkjf0hmln3kx";
+  };
+
+  # nix-locate needs the --db argument to be a directory containing a file
+  # named "files".
+  nixIndexDB = runCommand "nix-index-cache" {} ''
+    mkdir $out
+    ln -s ${indexCache.out} $out/files
+  '';
+
+in
+
+stdenv.mkDerivation rec {
+  name = "comma";
+
+  src = ./.;
+
+  buildInputs = [ nix-index.out nix.out fzy.out ];
+  nativeBuildInputs = [ makeWrapper ];
+
+  installPhase = let
+    caseCondition = lib.concatStringsSep "|" (overlayPackages ++ [ "--placeholder--" ]);
+  in ''
+    mkdir -p $out/bin
+    sed -e 's/@OVERLAY_PACKAGES@/${caseCondition}/' < , > $out/bin/,
+    chmod +x $out/bin/,
+    wrapProgram $out/bin/, \
+      --set NIX_INDEX_DB ${nixIndexDB.out} \
+      --prefix PATH : ${nix-index.out}/bin \
+      --prefix PATH : ${nix.out}/bin \
+      --prefix PATH : ${fzy.out}/bin
+
+    ln -s $out/bin/, $out/bin/comma
+  '';
+}