参考：
http://man.linuxde.net/tr
shell脚本学习指南
语法
tr [options] source-char-list replace-char-list
用途
转换字符。例如，将大写字符转换成小写。选项可让你指定要删除的字符，以及将一串重复出现的字符浓缩成一个。
Translate, squeeze, and/or delete characters from standard input, writing to standard output.
常用选项
-c或--complement：取代所有不属于第一字符集的字符；use the complement of source-char-list
-d或--delete：删除所有属于第一字符集的字符；delete characters in source-char-list, do not translate
-s或--squeeze-repeats：把连续重复的字符以单独一个字符表示；replace each input sequence of a repeated character that is listed in source-char-list with a single occurrence of that character.
-t或--truncate-set1：先删除第一字符集较第二字符集多出的字符。
支持的字符集
[:alnum:] all letters and digits
[:alpha:] all letters
[:blank:] all horizontal whitespace
[:cntrl:] all control characters
[:digit:] all digits
[:graph:] all printable characters, not including space
[:lower:] all lower case letters
[:print:] all printable characters, including space
[:punct:] all punctuation characters
[:space:] all horizontal or vertical whitespace
[:upper:] all upper case letters
[:xdigit:] all hexadecimal digits
[=CHAR=] all characters which are equivalent to CHAR
举例
将小写字符转换为大写字母
tr [:lower:] [:upper:]