shell 字符串、数字比较

二元比较操作符,比较变量或者比较数字.注意数字与字符串的区别. 
整数比较 
-eq &nbsp; &nbsp; &nbsp; 等于,如:if [ "$a" -eq "$b" ]&nbsp;-ne &nbsp; &nbsp; &nbsp; 不等于,如:if [ "$a" -ne "$b" ]&nbsp;-gt &nbsp; &nbsp; &nbsp; 大于,如:if [ "$a" -gt "$b" ]&nbsp;-ge &nbsp; &nbsp; &nbsp; 大于等于,如:if [ "$a" -ge "$b" ]&nbsp;-lt &nbsp; &nbsp; &nbsp; 小于,如:if [ "$a" -lt "$b" ]&nbsp;-le &nbsp; &nbsp; &nbsp; 小于等于,如:if [ "$a" -le "$b" ]&nbsp;< &nbsp; &nbsp; &nbsp; 小于(需要双括号),如:(("$a" < "$b"))&nbsp;<= &nbsp; &nbsp; &nbsp; 小于等于(需要双括号),如:(("$a" <= "$b"))&nbsp;> &nbsp; &nbsp; &nbsp; 大于(需要双括号),如:(("$a" > "$b"))&nbsp;>= &nbsp; &nbsp; &nbsp; 大于等于(需要双括号),如:(("$a" >= "$b"))&nbsp;
字符串比较&nbsp;= &nbsp; &nbsp; &nbsp; 等于,如:if [ "$a" = "$b" ]&nbsp;== &nbsp; &nbsp; &nbsp; 等于,如:if [ "$a" == "$b" ],与=等价&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 注意:==的功能在[[]]和[]中的行为是不同的,如下:&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 1 [[ $a == z* ]] &nbsp; &nbsp;# 如果$a以"z"开头(模式匹配)那么将为true&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 2 [[ $a == "z*" ]] # 如果$a等于z*(字符匹配),那么结果为true&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 3&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 4 [ $a == z* ] &nbsp; &nbsp; &nbsp;# File globbing 和word splitting将会发生&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 5 [ "$a" == "z*" ] # 如果$a等于z*(字符匹配),那么结果为true&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 一点解释,关于File globbing是一种关于文件的速记法,比如"*.c"就是,再如~也是.&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 但是file globbing并不是严格的正则表达式,虽然绝大多数情况下结构比较像.&nbsp;!= &nbsp; &nbsp; &nbsp; 不等于,如:if [ "$a" != "$b" ]&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 这个操作符将在[[]]结构中使用模式匹配.&nbsp;< &nbsp; &nbsp; &nbsp; 小于,在ASCII字母顺序下.如:&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; if [[ "$a" < "$b" ]]&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; if [ "$a" < "$b" ]&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 注意:在[]结构中"<"需要被转义.&nbsp;> &nbsp; &nbsp; &nbsp; 大于,在ASCII字母顺序下.如:&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; if [[ "$a" > "$b" ]]&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; if [ "$a" > "$b" ]&nbsp;&nbsp;&nbsp; &nbsp; &nbsp; 注意:在[]结构中">"需要被转义.&nbsp;-z &nbsp; &nbsp; &nbsp; 字符串为"null".就是长度为0.&nbsp;-n &nbsp; &nbsp; &nbsp; 字符串不为"null"