#!/bin/bash

pid=$1; shift

if [ -z "$pid" ]; then
  echo >&2 "Usage: readenv <pid> [<env> [<env> ...]]"
  exit 1
fi

xargs -n 1 -0 echo < /proc/$pid/environ | (
  if [ $# -gt 0 ]; then
    regex=
    for i in ${1+"$@"}; do regex="$regex|$i"; done
    regex=${regex#|}
    regex=${regex%|}
    [ -n "$regex" ] && regex="^($regex)="
    exec grep -E "$regex"
  else
    exec cat
  fi
)