Demonstrates how to test if there is data waiting on standard input (otherwise, we may wish to launch $EDITOR)

read-immediately.sh

#!/bin/sh

# This script depends on the read builtin and its -t (timeout)
# option. It is not standard, we have to test it.

# http://www.cyberciti.biz/tips/how-do-i-find-out-what-shell-im-using.html
shell=$(ps hp $$|awk '{print $5}')
if [ $shell != "zsh" ] && [ $shell != "bash" ] && [ $shell != "ksh" ]; then
    echo "Sorry, this script requires a shell with support of timeout in read. $shell is unknown to me." >&2
    exit 1
fi

if ! read -t 0 FIRSTLINE; then
    echo "Nothing on standard input"
else
    echo "There was something on standard input:"
    echo $FIRSTLINE
    cat -
fi

# Thanks to Yann Droneaud for the tip.

# Here is the documentation in zshbuiltins(1):
#
#             -t [ num ]
#                     Test  if input is available before attempting to read.  If num is present, it
#                     must begin with a digit and will be evaluated to give a  number  of  seconds,