#! /bin/sh
IFS=' '
case \ $*\  in
*\ -*) if test -t 0 -o -t 1
       then cat >> /dev/tty << eot
WARNING: bang does not accept any -flags, only files.

DESCRIPTION.
  bang is like cat but interprets !command escapes with either
  (1) SHELL=$SHELL, or
  (2) eval (if SHELL is empty or SHELL=eval)

USAGE.
  i (~saor) use bang as input to other commands:

	bang|dc
	!getconf INT_MAX

  to make simple/interactive notes:

	tee INDEX! | bang > INDEX
	welcome to my humble directory.
	!ls|nl
	^D (ctrl+d)

  and as a basic preprocessor to avoid painful shell quoting:

	SHELL=dc bang file

BUGS.
  bang can only handle one-liners.
  bang is inefficient, each !command is a new process.
  bang might strip spaces/tabs if IFS behaves weirdly
  bang chokes on null \000 bytes ^@
  bang behaves differently if stdout is not a terminal

eot
       fi
       ;;
esac
case "$#" in
\0) cat;;
*) while :
   do cat <"$1"
   case "$#" in
   \1) break;;
   esac
   shift
   done
   ;;
esac | while IFS='
'
read -r line
do case "$line" in
\!*) IFS=' 	'
     case $SHELL in
     ''|eval) eval "`sed 's/!//'`";;
     *) sed 's/!//' | $SHELL;;
     esac | if test -t 1
     then cat
     else tee -a /dev/tty
     fi
     ;;
*) cat;;
esac << eot
$line
eot
done