n与z的比较

-z，! -z与-n的分别

[root@web01-8 scripts]# [ -z "" ] && echo 1||echo 0     #-z表示0为真
1
[root@web01-8 scripts]# [ ! -z "" ] && echo 1||echo 0
0
[root@web01-8  scripts]# [ -n "" ] && echo 1||echo 0
0
[root@web01-8 scripts]# a="abc"
[root@web01-8 scripts]# [ -z "$a" ] && echo 1||echo 0   #零为真
0
[root@web01-8 scripts]# [ -n "$a" ] && echo 1||echo 0
1

系统脚本示例：

[root@web01-8 scripts]# sed -n '30,31p' /etc/init.d/network 
# Check that networking is up.
[ "${NETWORKING}" = "no" ] && exit 6                                  #空格冒号
[root@web01-8 scripts]# sed -n '18,22p' /etc/init.d/rpcbind           #空格冒号
if [ "$LANG" = "ja" -o "$LANG" = "ja_JP.eucJP" ]; then
    if [ "$TERM" = "linux" ] ; then
        LANG=C
    fi
fi