Shell 问题？

zt2620zt

1.$ [ -f /tmp/test.txt ] || > /tmp/test.txt


1.$ echo $?; echo $!; echo $$
1.￥var=`grep “upe” notes.txt 3>&2 2>&1 1>&3`; echo $var

2.$ df | sed -n 's/.* \([0-9][0-9]*\)%.*/\1/p'

3.$ while who | grep “^upe” > /dev/null; do
> sleep 60
> done; echo “the cat’s away…”

4.$ set `who | cut –c1-8 | sort -u`; for i; do
> echo “Dear $i” | cat – form_letter | lpr
> done;

说明各行命令的功能和含义？好了好久都找不到，麻烦各位看看了！

four

去shell版问嘛

pointer

又是作业？又是作业？又是作业？