Strange character in a file

Question

I have an UTF-8 file that contains a strange character -- visible to me just as

<96>

This is how it appears on vi

and how it appears on gedit

and how it appears under LibreOffice

and that makes a series of basic Unix tools misbehave, including:

1. cat file make the character dissapear, and more as well
2. I cannot copy and paste inside vi/vim -- it will not even find itself
3. grep fails to display anything as well, as if the character did not exists.

The program file works fine and recognizes it an UTF-8 file. I also know that, because of the nature of the file, it most likely came from a Copy & Paste from the web and the character initially represented an EMDASH.

My basic questions are:

1. Is there anything wrong with this file?
2. How can I search for other occurrences of it inside the same file?
3. How can I grep for other files that may contain the same problem/character?

The file can be found here: file.txt

Answer 1

This file contains bytes C2 96, which are the UTF-8 encoding of codepoint U+0096. That codepoint is one of the C1 control characters commonly called SPA "Start of Guarded Area" (or "Protected Area"). That isn't a useful character for any modern system, but it's unlikely to be harmful that it's there.

The original source for this was likely a byte 0x96 in some single-byte 8-bit encoding that has been transcoded incorrectly somewhere along the way. Probably this was originally a Windows CP1252 en dash "–", which has byte value 96 in that encoding - most other plausible candidates have the control set at positions 80-9F - which has been translated to UTF-8 as though it was latin-1 (ISO/IEC 8859-1), which is not uncommon. That would lead to the byte being interpreted as the control character and translated accordingly as you've seen.

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You can fix this file with the iconv tool, which is part of glibc.

iconv -f utf-8 -t iso-8859-1 < mwe.txt | iconv -f cp1252 -t utf-8

produces a correct version of your minimal example for me. That works by first converting the UTF-8 to latin-1 (inverting the earlier mistranslation), and then reinterpreting that as cp1252 to convert it back to UTF-8 correctly.

It does depend on what else is in the real file, however. If you have characters outside Latin-1 elsewhere it will fail because it can't encode those correctly at the first step.

If you don't have iconv, or it doesn't work for the real file, you can replace the bytes directly using sed:

LC_ALL=C sed -e $'s/\xc2\x96/\xe2\x80\x93/g' < mwe.txt

This replaces C2 96 with the UTF-8 en dash encoding E2 80 93. You could also replace it with e.g. a hyphen or two by changing \xe2\x80\x93 into --.

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You can grep in a similar fashion. We're using LC_ALL=C to make sure we're reading the actual bytes, and not having grep interpret things:

LC_ALL=C grep -R $'\xc2\x96` .

will list out everywhere under this directory those bytes appear. You may want to limit it to just text files if you have mixed content around, since binary files will include any pair of bytes fairly often.

Answer 2

0x96 is an en dash in the Windows codepage 1252. The c2 byte preceding it seems to be a default first byte in a double-width character. Someone else could explain more precisely about it.

To search for other occurrences, put your cursor over it in command mode, hit yl (yank one character), then type /<Ctrl>+r". (ctrl+r lets you insert the contents of a register into the command, and the " register is whatever has last been yanked).

Just replace it with two hyphens if you want it to render in your terminal. If that is a bibtex file that you have, then two hyphens are the appropriate way to key it in.

To show how you can find occurrences of the character, you can pipe it through a hexdump tool like xxd.

$ cat tmp | xxd | grep c296
00000000: 7061 6765 733d 7b31 c296 3935 7d2c 0a70  pages={1..95},.p
00000020: 6765 733d 7b31 c296 3935 7d2c 0a70 6167  ges={1..95},.pag
00000040: 733d 7b31 c296 3935 7d2c 0a70 6167 6573  s={1..95},.pages
00000060: 7b31 c296 3935 7d2c 0a70 6167 6573 3d7b  {1..95},.pages={
00000080: c296 3935 7d2c 0a70 6167 6573 3d7b 31c2  ..95},.pages={1.
00000090: 9639 357d 2c0a 7061 6765 733d 7b31 c296  .95},.pages={1..
000000b0: 357d 2c0a 7061 6765 733d 7b31 c296 3935  5},.pages={1..95
000000d0: 2c0a 7061 6765 733d 7b31 c296 3935 7d2c  ,.pages={1..95},
000000f0: 7061 6765 733d 7b31 c296 3935 7d2c 0a70  pages={1..95},.p
00000110: 6765 733d 7b31 c296 3935 7d2c 0a70 6167  ges={1..95},.pag
00000130: 733d 7b31 c296 3935 7d2c 0a70 6167 6573  s={1..95},.pages
00000150: 7b31 c296 3935 7d2c 0a70 6167 6573 3d7b  {1..95},.pages={

Answer 3

The text in your file is pages = {1113},, yes it looks like the number 1113 but actually there is a different character after the first 1. And, yes, you can copy-paste the string from the edit link for this web page to get the encoded character.

We can look inside the string with some tools:

$ a='pages = {1113},'

Or, to make it explicitly clear and allow an easy copy-paste without using the edit page:

$ a=$(printf 'pages = {1\xc2\x96113},') 

$ echo "$a" | od -An -tx1c
  70  61  67  65  73  20  3d  20  7b  31  c2  96  31  31  33  7d
   p   a   g   e   s       =       {   1 302 226   1   1   3   }
  2c  0a
   ,  \n

$ echo "$a" | sed -n l
pages = {1\302\226113},$

$ echo "$a" | xxd
00000000: 7061 6765 7320 3d20 7b31 c296 3131 337d  pages = {1..113}
00000010: 2c0a

So, the character is two bytes values c2 96 (in hex) or 302 226 (in octal).
It probably is the UTF-8 encoding of a byte value of 96, or expressed as an Unicode character: U-0096.

That value, in present times UTF-8, or better yet, in ISO-8859-1, is a control character in the C1 region of control characters(Wikipedia page) and (Unicode PDF) that goes from 128 to 159 in decimal. In specific, the U-0096 is called "START OF GUARDED AREA" or SPA.

That value (dec 150) is beyond the ASCII range (0-127) and was (in older times) used to represent several characters depending on the code-page used. It seems reasonable to assume that is was previously a dash (to mark the range 1-113) as encoded in Windows-1252 (Microsoft page) (Wikipedia 1252) and called an en dash (which is the smaller of the two dashes en and em) (Wikipedia en dash) or simply, in layman terms, a dash (-).

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Q1: Is there anything wrong with this file?

Not really, control characters are valid characters, rarely used but valid none-the-less.

But you may replace them with a dash to make editing easier.

<file.txt sed 's/\xc2\x96/-/'

Q2 - How can I search for other occurrences of it inside the same file?

sed -n '/\xc2\x96/p'             # will print lines that contain that character.

Or, grep could search for the character (the color highlight will not be visible as the character is non-printable) and print the line.

c="$(printf "\U96")" ; grep "$c" file.txt

Or more broad, find all characters in that control character range and list the files that contain such characters:

grep -rlP "[\x80-\x9f]"    

Q3 - How can I grep for other files that may contain the same problem/character?

This will list (-l) the files that match the character.

grep -rlP "\x96"