正则表达式 $'s/\r$//' 有什么作用？

Question

Todd Schneider 在他的NYC Taxi Data Analysis 中使用以下命令为 PostresSQL 准备一个 CSV 文件。

sed $'s/\r$//' $filename | sed '/^$/d' | ...

第二个 sed 命令删除空行。第一个是做什么的？

Answer 1

根据man bash：

  Words of the form $'string' are treated specially.  The word expands to
   string,  with backslash-escaped characters replaced as specified by the
   ANSI C standard.  Backslash escape sequences, if present,  are  decoded
   as follows:                                      
          \a     alert (bell)                       
          \b     backspace                          
          \e                                        
          \E     an escape character                
          \f     form feed                          
          \n     new line                           
          \r     carriage return                    
          \t     horizontal tab                     
          \v     vertical tab                       
          \\     backslash                          
          \'     single quote                       
          \"     double quote                       
          \?     question mark                      
          \nnn   the  eight-bit  character  whose value is the octal value
                 nnn (one to three digits)          
          \xHH   the eight-bit character whose value  is  the  hexadecimal
                 value HH (one or two hex digits)   
          \uHHHH the  Unicode (ISO/IEC 10646) character whose value is the
                 hexadecimal value HHHH (one to four hex digits)
          \UHHHHHHHH                                
                 the Unicode (ISO/IEC 10646) character whose value is  the
                 hexadecimal value HHHHHHHH (one to eight hex digits)
          \cx    a control-x character              
  The  expanded  result  is  single-quoted, as if the dollar sign had not
   been present.

因此$'s/\r$//'删除CR行尾的 ASCII 。这是将 Windows 行尾转换为 UNIX 行尾的粗略方法。