catが呼び出す外部変数
open
今回の肝
http://www.jp.freebsd.org/cgi/mroff.cgi?subdir=man&lc=1&cmd=&man=open&dir=jpman-6.0.0%2Fman§=0
isascii
http://www.jp.freebsd.org/cgi/mroff.cgi?subdir=man&lc=1&cmd=&man=isascii&dir=jpman-6.0.0%2Fman§=0
isprint
http://www.jp.freebsd.org/cgi/mroff.cgi?subdir=man&lc=1&cmd=&man=isprint&dir=jpman-6.0.0%2Fman§=0