awk 的RS 为空，以什么为行分隔符？

ljt2k

awk 的RS 为空，以什么为行分隔符？


看到有的文档说是以连续的换行为“行分隔符”；
有的说以整个内容为一行？

试了一下，好像不同的环境，处理是不同的？

liion631818

回复 1# ljt2k


    LZ意思RS=""， 书上是这么说的，RS="", 就是以空白行为记录的分隔符，就是这么设计的，不解释。。

jagel

哈哈

ljt2k

请看一下下面两种不同的说明：


      RS
            Input record separator (default is a new-line character). If the RS special variable is null, records are
            separated by sequences of one or more blank lines; leading or trailing blank lines do not result in empty
            records at the beginning or end of input; and the new-line character is always a field separator, regardless
            of the value of the FS special variable.





Normally, AWK reads one line at a time, and breaks up the line into fields. You can set the "RS" variable to change AWK's definition of a "line." If you set it to an empty string, then AWK will read the entire file into memory. You can combine this with changing the "FS" variable.

liion631818

第一点：
当RS=""时， 开始和结尾的空白行会被忽略掉，就跟FS为默认值时，行开头和结尾的空白字符被忽略一样，
and the new-line character is always a field separator
这句话的意思是换行符是域分隔符，而且只是是其中之一，应该在并上设置的FS的值，例如

1. 
   
2. cat file
   
3. 1 xx
   
4. 2 xx
   
5. 3
   
6. 4
   
7. awk -vRS="" '{print $1, $2, $3}' file
   
8. 1 xx 2
   

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此时，空白，tab和换行都是域分隔符
同理，可以理解：

1. 
   
2. $ cat file
   
3. 1#xx
   
4. 2#xx
   
5. 3
   
6. 4
   
7. awk -vRS="" -vFS="#" '{print $1, $2, $3}' file
   
8. 1 xx 2
   

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第二点：
个人感觉 AWK will read the entire file into memory应该包含一个假设条件，就是整个文件除了开头和结尾没有空白行

ljt2k

回复 6# liion631818


    谢谢解释！

waker

1. 
   
2. RS == "\n"
   
3.     Records are separated by the newline character (`\n'). In effect, every line in the data file is a separate record, including blank lines. This is the default.
   
4. RS == any single character
   
5.     Records are separated by each occurrence of the character. Multiple successive occurrences delimit empty records.
   
6. RS == ""
   
7.     Records are separated by runs of blank lines. The newline character always serves as a field separator, in addition to whatever value FS may have. Leading and trailing newlines in a file are ignored.
   
8. RS == regexp
   
9.     Records are separated by occurrences of characters that match regexp. Leading and trailing matches of regexp delimit empty records. (This is a gawk extension; it is not specified by the POSIX standard.)
   

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RS=""时心空行为记录分割符

zzy7186

学习

jack1007

RS 默认是换行为分隔符，文件首尾的忽略，这个和FS类似