Comments on Why does the file command fail to recognize non-text files as such?
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Why does the file command fail to recognize non-text files as such?
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Text file as
A file that contains characters organized into zero or more lines. The lines do not contain NUL characters and none can exceed {LINE_MAX} bytes in length, including the <newline> character.
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Line as
A sequence of zero or more non- <newline> characters plus a terminating <newline> character.
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Character as
A sequence of one or more bytes representing a single graphic symbol or control code.
Consider then six files, each with two bytes, created with these Printf commands (using octals):
printf "\101\012" > file1 #A<newline>
printf "\010\012" > file2 #<backspace><newline>
printf "\101\101" > file3 #AA
printf "\200\012" > file4
printf "\200\200" > file5
printf "\000\012" > file6 #<null><newline>
Now, in the UTF-8 encoding, the octal 012 (0x0A) is the newline character, 101 (0x41) is the graphic
symbol A, 010 (0x08) is the backspace control character and 200 (0x80) is a continuation byte that never occurs as the first byte of a multi-byte sequence, so it does not form a valid character.
Hence, I would regard files 1 and 2 as text files, but the remaining as non-text files, because file 3 is not newline terminated, files 4 and 5 have an invalid character and file 6 contains a null byte.
However, the file command does not seem to completely agree
with me; it lists files 3, 4 and 5 as text files,
$ file --mime-type file*
file1: text/plain
file2: text/plain
file3: text/plain
file4: text/plain
file5: text/plain
file6: application/octet-stream
Why does the file command fail to identify files 3, 4 and 5 as non-text files
(I'm assuming it can't possibly be a bug) even though I use en_US.UTF-8 as my locale, or else what did I incorrectly
understand?
Post
https://theasciicode.com.ar/extended-ascii-code/majuscule-c-cedilla-uppercase-ascii-code-128.html
Octal 101 is 65, which is ASCII/UTF-8 for A - a valid character.
Octal 200 is 128, which is ASCII/UTF-8 or whatever for Ç - which is also a valid character.
A file that contains characters organized into zero or more lines.
Lines are newline characters, which are octal 012. The above rule means newlines can appear, but don't have to.
Really, as long as the file contains no zero bytes (which are NUL), it's a text file.
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