1. 用途：
tr，translate的简写，主要用于压缩重复字符，删除文件中的控制字符以及进行字符转换操作。
2. 语法：
tr [OPTION]... SET1 [SET2]
3. 参数：
-s：squeeze-repeats压缩重复字符，使用SET1中列举的单一字符替换输入流中的重复字符
[root@bogon ~]# echo "aaabbbaacccfdddccc" | tr -s [abcdf] abacfdc
-d：删除字符
[root@bogon ~]# echo "a1b2c3z4" | tr -d "[a-z][A-Z]" 1234
-t：替换字符。将SET1中字符用SET2对应位置的字符进行替换，默认值为-t
[root@bogon ~]# echo "a1b2c3d4" | tr -t [abc] [XYZ] #将a转换成X，b转换成Y，c转换成Z X1Y2Z3d4
[root@bogon ~]# echo "hello world" |tr -t [:lower:] [:upper:] #将小写转换成大写
HELLO WORLD
-c：complement，用SET2替换SET1中没有包含的字符
[root@bogon ~]# echo "aaabbbccc" | tr -c [ab] "z" | tr -s [z] | tr -c [ab] " " #1.将ab以为的字符替换成z; 2.压缩重复项z; 3.将ab以为的字符替换成换行 aaabbb
解析字符串：
NNN character with octal value NNN (1 to 3 octal digits) \ backslash a audible BEL backspace f form feed new line return horizontal tab v vertical tab CHAR1-CHAR2 all characters from CHAR1 to CHAR2 in ascending order [CHAR*] in SET2, copies of CHAR until length of SET1 [CHAR*REPEAT] REPEAT copies of CHAR, REPEAT octal if starting with 0 [: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