parse a block of code correctly even with heredocs or compound commands or pipelines or ...

timer

#!/bin/bash
shopt -s expand_aliases extglob

__eval () {
  unset __code __tmp __commands
  while (( $# )); do
    if [[ $1 && $1 = *[![:space:]]* ]]; then
      printf "==== command ====\n%s\n=================\n" "$1"
      time eval "$1"
    fi
    shift
  done
}

__analyzetimer () {
  local __code __commands=('') __tmp

  IFS= read -rd '' -u"$__timer" __code
  exec {__timer}>&-


  # stupid way to check if a string is valid syntax
  if [[ $(bash -O extglob -nc -- "$__code" 2>&1) ]]; then
  # check syntax with bash -n, then check if bash printed an error message
  # exit status is not enough, e.g.: bash -nc ': << x' returns 0
    echo "that doesn't look like valid syntax" >&2
    return 1
  fi


  # sorta-parser
  # this could probably be cleaner with =~
  # but this way BASH_REMATCH is kept intact
  while [[ ${#__code} -ne 0 && ${__code} = *[$'\n&;#']* ]]; do
    # get text up to (and including) next \n or & or ;
    __tmp=${__code%%[$'\n&;#']*}
    __tmp=${__code::${#__tmp}+1}
    __code=${__code:${#__tmp}}

    # add it to array
    __commands[-1]+=$__tmp

    # if this isn't valid syntax, we're inside one of:
    # - comsub
    # - procsub
    # - compound command
    # - some kind of quoting
    # so we don't start a new command
    if [[ ! $(bash -O extglob -nc -- "$__code" 2>&1) ]]; then

      # check if the last character was escaped, in which case don't start a new one
      __tmp=-2
      # if this is a backslash, maybe it also was escaped
      while [[ ${__commands[-1]:__tmp--:1} = '\' ]]; do
        [[ ${__commands[-1]:__tmp--:1} = '\' ]] || break
      done

      # now if __tmp is *even*, we found an *odd* number of \ so it was escaped
      if (( __tmp % 2 )); then

        __tmp=0
        # handle special cases
        case ${__commands[-1]: -1} in
          '#') # remove everything up to end of line
            __commands[-1]=${__commands[-1]::-1}
            __code=${__code#*$'\n'} ;;
          '&') # if it's part of &&, don't start a new command
            [[ ${__code::1} = '&' ]] && __tmp=1 ;;
        esac

        # if everything is ok, we're done!
        if [[ __tmp -eq 0 && ! $(bash -O extglob -nc -- "${__commands[-1]}" 2>&1) ]]; then
          # clean it up and start a new command
          __tmp=${__commands[-1]##+([$' \t\n'])}
          __commands[-1]=${__tmp%%+([$' \t\n'])}
          __commands+=('')
        fi
      fi
    fi
  done

  (( ${#__code} )) && commands+=("$__code")
  __eval "${__commands[@]}"
}

alias $'timer{=__analyzetimer {__timer}<< \\}timer\n'












timer{
  true &&
  echo 'hello $( world )' ";" \\\; /!(bin|usr) \
    foo bar || echo false \\ \\\\;

  if false; then
    echo it was true
  else
    case foo in
      foo) echo 'it was false and it matched foo 
newline';;
      bar) echo something went really wrong ;;
    esac
  fi

  echo "background: $BASHPID" & wait # you can also use comments
  echo "foreground: $BASHPID"

  while read -r; do
    echo "${REPLY^^}!!!!"
  done << x
this is $(echo sparta)
x
  echo x | cat -n
  echo y |& cat -n
}timer