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--- characters_filenames [2019-09-21 19:31:04]
mi created
+++ characters_filenames [2020-06-20 23:14:40] (current)
mi [Path separators]
@@ Line 1: / Line 1: @@
 ====== Characters in file names ======
+Note : this page often uses "Unix" for non-Windows systems, because Mac OS and Linux are both Unix-based systems. And the Web standard also originated on Unix systems, so for example, it's path separator is the same "/".
+===== Path separators =====
+* / in Unix and on the web. Windows also accpts it in some contexts, but sometimes not.
+* \ in Windows. But it's an escape character in Unix.
+* : was used in the old Mac OS up to version 9. See the [[#Mac : / confusion]] below.
+===== Escape characters =====
+  * \ Unix escape
+  * ^ Windows cmd.exe escape
+  * ` Windows PowerShell escape
+(see also https://en.wikipedia.org/wiki/Escape_character)
 ===== Windows Powershell =====
 The Windows Powershell (v. 2 in Win7) has a function `GetInvalidFileNameChars()` :
-<code>ForEach ($c in [System.IO.Path]::GetInvalidFileNameChars()) { $i=([int]$c); "{0,3:d}    {1,2:x2}    {2,1}" -f $i,$i,$c }
+<code>
-    22    "
+[System.IO.Path]::GetInvalidFileNameChars() | ForEach-Object {$i=[int]$_; '{0,3}  {1:X2}  {2}' -f $i,$i,$_ } | Sort-Object
-    3c    <
+  00
-    3e    >
+  01  ☺
-    7c    |
+  02  ☻
-    00
+  03  ♥
-    01    ☺
+  04  ♦
-    02    ☻
+  05  ♣
-    03    ♥
+  06  ♠
-    04    ♦
+  07
-    05    ♣
+  08
-    06    ♠
+  09
-    07
+  0A
-    08
-    09
-    0a
-    0b    ♂
+  0B  ♂
-    0c    ♀
+  0C  ♀
-    0d
+  0D
-    0e    ♫
+  0E  ♫
-    0f    ☼
+  0F  ☼
-    10    ►
+  10  ►
-    11    ◄
+  11  ◄
-    12    ↕
+  12  ↕
-    13    ‼
+  13  ‼
-    14    ¶
+  14  ¶
-    15    §
+  15  §
-    16    ▬
+  16  ▬
-    17    ↨
+  17  ↨
-    18    ↑
+  18  ↑
-    19    ↓
+  19  ↓
-    1a    →
+  1A  →
-    1b    ←
+  1B  ←
-    1c    ∟
+  1C  ∟
-    1d    ↔
+  1D  ↔
-    1e    ▲
+  1E  ▲
-    1f    ▼
+  1F  ▼
-    3a    :
+  22  "
-    2a    *
+  2A  *
-    3f    ?
+  2F  /
-    5c    \
+  3A  :
-    2f    /
+  3C  <
+  3E  >
+  3F  ?
+  5C  \
+  7C  |
 </code>
+So it lists the obvious control characters 0 to 31 (x00-x1F), plus
+  * "
+  * *
+  * /
+  * :
+  * <
+  * >
+  * ?
+  * \
+  * |
+===== At start or end of file name =====
+  * space at the end of a file or directory name is ignored/removed by Windows. It is OK in Unix, but obviously a problem because it's invisible.
+  * . dot at the end of a file or directory name is ignored/removed by Windows.
+  * . dot at the start of a file or directory name makes it "hidden" in Unix. It will not show in normal directory listings and file managers.
+===== Mac : / confusion =====
+Mac OS in the eighties and nineties (up to version 9) was not a Unix-based system, and used ":" as a path separator. "/" had no special meaning for Macs, so it was accepted in file names like "report 25/3/1992".
+When Mac replaced it's OS with Unix, "/" became an invalid character in file names, but on the other hand, ":" was now a perfectly normal character. So it decided to silently replace all "/" with ":", and made it's graphical interface handle the translation invisibly. So you can still see this "report 25/3/1992" file in the Finder, and you can have the impression that you can still write a file named "report 25/12/2019". However, the real file name in the file system will be "report 25:3:1992", and some Mac programs will only see the real file name and not "translate" it on the fly.

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