tr

论文遇到了瓶颈，歇一歇，没用awk完成，纯粹是休息下……

tr [OPTION]    SET1   [SET2]    file

说明：

     tr -s  SET1 file  :对于给定的文段，将凡在SET1中的出现的连续的字符都压缩成一个字符。

echo "abaa    ddxx   gg" | tr -s 'a dxg'
结果：aba dx g

     tr -d SET1 file ：对于给定的文段，删除所有在SET1中出现的字符。

     tr -t SET1 SET2 file : 将SET1 截断成SET2长度，然后依SET1和SET2中字符出现的次序依次做替换。

ls -l *media* | tr -s ' ' | cut -d ' ' -f 9

     tr -c SET1 [SET2] file : 对于给定的文段，对SET1的补集做操作，一般同其它选项结合使用。

    SETs是指定的字符（串），可以转换的字符如下：

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（升序） 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

 将多个空格转成一个空格：
1、用awk:
　　awk '{print $2}' file
2、一定要用cut的话：
　　cat file|tr -s ' '|cut -d' ' -f2