A convenience shell wrapper around the nix function unsafeGetAttrPos.

nix-findattr

#!/bin/sh

pname="$(basename "$0")"
read -d '' usage <<EOF
Usage: $pname -h|--help
       $pname [-n <number of context lines>] [attrset (default: nixpkgs)] <attr name>
EOF

attrset="import <nixpkgs> {}"
n=3

case "$1" in
    -h | --help ) echo "$usage" >&2; exit;;
    -n )          n="$2"; shift 2;;
esac
if [ "$#" -gt 1 ]; then
    attrset="$1"
    shift
fi
attr="$1"
    
read -d '' expr <<EOF
let
  inherit (builtins.unsafeGetAttrPos "${attr}" (${attrset})) file line;
in "\${file}:\${builtins.toString line}"
EOF

attrPos="$(nix eval --raw "($expr)")"

file="${attrPos%:*}"
line="${attrPos##*:}"

if [ $n -gt 0 ]; then
    context="-e $((line-n)),$((line-1))p -e $((line+1)),$((line+n))p"
fi

echo "${attrPos}:"
sed -n $context -e ${line}'s/^.\+$/&/gp' "$file"