1.test,/usr/bin/test,[],和/usr/bin/[介绍
首先，linux下test,/usr/bin/test,[],和/usr/bin/[命令都是等价命令
其次，linux下test,/usr/bin/test,[],和/usr/bin/[命令一般用来测试文件类型，或者用来比较字符串
test,/usr/bin/test,[],和/usr/bin/[命令的区别：
1.test是shell内建命令
[root@elasticsearch ~]# type test
test is a shell builtin
[root@elasticsearch ~]#2./usr/bin/test是外部命令
[root@elasticsearch ~]# type /usr/bin/test
/usr/bin/test is /usr/bin/test
[root@elasticsearch ~]#3.[]，[是shell内建命令，需与]配合结尾
[root@elasticsearch ~]# type [
[ is a shell builtin
[root@elasticsearch ~]# type ]
-bash: type: ]: not found
[root@elasticsearch ~]#4./usr/bin/[是外部命令
[root@elasticsearch ~]# type /usr/bin/[
/usr/bin/[ is /usr/bin/[
[root@elasticsearch ~]#2.test,/usr/bin/test,[],和/usr/bin/[用法举例
样例：
[root@elasticsearch ~]# cat test.sh
#!/bin/bash
echo "1.test testing"
if test -z "$1"
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
echo "2./usr/bin/test testing"
if /usr/bin/test -z "$1" #与内建的"test"命令结果相同.
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
echo "3.[] testing"
if [ -z "$1" ]
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
if [ -z "$1" #虽能运行，但是bash会报错，提示缺少关闭条件测试的右中括号.
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
echo "4./usr/bin/[ testing"
if /usr/bin/[ -z "$1" ]
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
if /usr/bin/[ -z "$1" #虽能运行，但是bash会报错，提示缺少关闭条件测试的右中括号.
then
echo "No command-line arguments."
else
echo "First command-line argument is $1."
fi
echo
exit 0
[root@elasticsearch ~]# sh test.sh ztj
1.test testing
First command-line argument is ztj.
2./usr/bin/test testing
First command-line argument is ztj.
3.[] testing
First command-line argument is ztj.
test.sh: line 27: [: missing `]'
First command-line argument is ztj.
4./usr/bin/[ testing
First command-line argument is ztj.
/usr/bin/[: missing ']'
First command-line argument is ztj.
[root@elasticsearch ~]#
