====== File Format ======


===== 개요 =====
  - 'fileformat' ('ff' for short) controls the way that Vim handles different line-ending sequences. 
  - Vim recognizes three file formats: unix, dos, and mac. 
  - Each of these file formats differs in the line-ending character sequences used on disk. 

^ OS ^ Format ^ 키 or ASCII ^
^ Unix | <LF> (line feed) | ''%%^J or 0x0A%%'' |
^ Mac  | <CR> (carriage return) | ''%%^M or 0x0D%%'' | 
^ Dos  | <CR><LF> | ''%%^M^J or 0x0D0A%%'' |


===== Format conversion =====
  - Assuming that the fileformat has been properly detected (see below), \\ it is very simple to convert to a different format. 
  - Simply set 'ff' to the desired format name; for example, \\ if you are editing a dos file and want to convert to unix, just do **:set ff=unix**.
  - That's it. The next time the file is written, unix line ends will be used. 
  - Things are a little tougher when your file has different ending sequences on different lines; \\ this situation is discussed below

===== Mass conversion =====
  - As absolon was kind enough to point out in #vim, you can do mass conversion from the shell like so <code>
vim +"argdo set ff=<format>" +wqa <files>
</code>
  - This will set 'fileformat' for each file in the argument list, then quit, saving all files.
  - See :help argdo and **:help -c** if you need more detail on what this does and why.

===== 'ff' Detection -- 'fileformats' =====

  - When reading a file, Vim tries to detect the proper fileformat. 
  - The way it does this is controlled by the 'fileformats' ('ffs') option. 
  - 'ffs' contains a comma separated list of the formats to try. 
  - Each platform has its own default value for 'ffs':

^unix | ffs=unix,dos |
^ dos / windows | ffs=dos,unix |
^ mac | ffs=mac,unix,dos |

  - Basically, Vim tries to find a line-ending sequence which appears at the end of every line, \\ and then uses that for 'ff'. 
  - This process can get fooled in two ways:
    - The true fileformat is not found in 'fileformats', \\ eg a Mac file on a Unix platform using the defaults 
    - There is a mix of line-ending sequences. \\ This can happen when mixing tools made for different platforms. 




===== When Detection Goes Awry =====
  - When 'ff' is not detected correctly, \\ you will usually see part or all of the line ending sequences in the editor window. 
  - Here is a short illustration of what you see when a mismatch happens.

| File contents | Line 1 \\ Line 2 |
| unix line-ends, ff=mac | ''%%Line 1^JLine 2^J%%'' |
| unix line-ends, ff=dos | Line 1 \\ Line 2 |
| dos line-ends, ff=unix | ''%%Line 1^M%%'' \\ ''%%Line 2^M%%'' |
| dos line-ends, ff=mac | ''%%Line 1%%'' \\ ''%%^JLine 2%%'' \\ ''%%^J%%'' |
| mac line-ends, ff=unix | ''%%Line 1^MLine 2^M%%'' |
| mac line-ends, ff=dos  | ''%%Line 1^MLine 2^M%%'' |
 



===== Fixing Detection Problems =====

  - If your file has consistent line endings throughout, \\ but you have had a 'ff' detection problem, \\ the best fix is to force Vim to use the correct format with the **:e** command: <code>
:e ++ff=mac
</code>

===== Fixing Inconsistent Line Endings =====
  - If you have extra leading or trailing characters (^M in unix or ^J in mac), use **:%s/\r/''/''** to remove them. 
  - If you have long lines (mac line-ends with ff=dos or unix, unix line ends with ff=mac), use **:%s/\r/\r/g** to replace the wrong line-ends with the correct line-ends. 
  - If you are curious, the reasoning behind this methodology appears below.


===== The Nitty-Gritty (핵심) =====
  - :substitute can be tricky when dealing with CR and NL. 
  - The problem stems from the fact that Vim uses NL in memory to represent a Nul character (see :help NL-used-for-Nul). 
  - The result of this is that unexpected things tend to happen when you try to modify line-endings using :s. 
  - Vim help says that \r matches CR and \n matches an end-of-line. 
  - In fact, when you use :s, \r will match CR or LF, depending on the fileformat! 
  - Basically, it matches whichever control character (^M or ^J) you see in the editor window. 
  - Furthermore, in the replace pattern, \n will expand to a LF, which then gets interpreted as... a Nul! (see :help sub-replace-special). 
  - Fortunately, when \r is used in the replace pattern, it is interpreted as a line-end, which will then display (and get written) as desired.