49

I have a file in UTF-8 encoding with BOM and want to remove the BOM. Are there any linux command-line tools to remove the BOM from the file?

$ file test.xml
test.xml:  XML 1.0 document, UTF-8 Unicode (with BOM) text, with very long lines
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61

If you're not sure if the file contains a UTF-8 BOM, then this (assuming the GNU implementation of sed) will remove the BOM if it exists, or make no changes if it doesn't.

sed '1s/^\xEF\xBB\xBF//' < orig.txt > new.txt

You can also overwrite the existing file with the -i option:

sed -i '1s/^\xEF\xBB\xBF//' orig.txt
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  • 4
    this may not work in a utf8 locale, but prepending a locale override to c or posix will always work. – hildred Jul 23 '17 at 15:29
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    @hildred I've tested it with the en_US.UTF-8 locale and it worked. When will it fail? – m13r Jul 24 '17 at 6:55
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    @m13r, It depends on the version of sed and compile options. In the failure case a very new version of sed with Unicode character classes will bring the three byte sequence in as a single character which does not match the three character sequence. However in such case you can do a sixteen bit character match. However this is a new feature and not universally present. If you want to test I recommend compiling the latest version. – hildred Jul 24 '17 at 16:25
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    To fix it to work with a unicode-enabled sed do LC_ALL=C sed '1s/^\xEF\xBB\xBF//' – Joshua Jul 24 '17 at 17:41
  • @CSM nice, but for one special case it does not work: Bevore: -<U+FEFF>\chapter{xxx} After: +\chapter{xxx}^M Explanation: Using MS-word for typos in latex-file. Latex under Linux is showing errors mentioned. Output is from a git system. How could I alter the expression to catch this special case too? – Cutton Eye Feb 20 '18 at 15:55
54

A BOM doesn't make sense in UTF-8. Those are generally added by mistake by bogus software on Microsoft OSes.

dos2unix will remove it and also take care of other idiosyncrasies of Windows text files.

dos2unix test.xml
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  • 14
    I agree that a UTF-8 encoded BOM does not make sense, but believe it or not, there are lots of people who think it is a great idea that helps differentiate UTF-8 from other 8-bit encodings. So it is a matter of taste. Windows Notepad adds a BOM on purpose. – Johan Myréen Jul 23 '17 at 14:02
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    What does it matter if it makes sense or not, when the context is just a question on how to remove it? According to Wikipedia, Notepad requires the BOM to recognize a file as UTF-8, and Google Docs also adds it while exporting a file as text. I doubt they all do it by mistake. – ilkkachu Jul 23 '17 at 14:09
  • Comments are not for extended discussion; this conversation has been moved to chat. – terdon♦ Jul 24 '17 at 14:07
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    Is there a way of not converting the line endings and just remove the BOM with dos2unix? – m13r Jul 25 '17 at 7:55
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    @m13r Then use the sed script in this answer. That will remove only the bom (if it exist), nothing else will be changed. – Arrow Jul 26 '17 at 5:51
23

It is possible to remove the BOM from a file with the tail command:

tail -c +4 withBOM.txt > withoutBOM.txt
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  • 1
    Why 4? The BOM has 3 byte. – deviantfan Jul 23 '17 at 17:12
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    @deviantfan Which is why you need to start at the 4th byte if you want to skip it. – Stéphane Chazelas Jul 23 '17 at 18:33
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    tail is using 1 based indexing?! WTF! – CodesInChaos Jul 23 '17 at 19:31
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    @CodesInChaos, tail -c -1 or tail -c 1 (what tail is generally used for) is the content starting with the last byte, tail -c +1 starting with the first byte. tail -c 0/tail -c +0 for that would be a lot more unintuitive. – Stéphane Chazelas Jul 23 '17 at 23:05
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    @deviantfan: (dd bs=1 count=3 of=/dev/null; cat) <input >output. Or with GNU (head -c3 >/dev/null; cat) -- even in UTF8 or other non-singlebyte locale; GNU head does 'char'=byte. – dave_thompson_085 Jul 24 '17 at 6:16
17

Using VIM

  1. Open file in VIM:

    vi text.xml

  2. Remove BOM encoding: 

    :set nobomb

  3. Save and quit:

    :wq
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4

You can use

LANG=C LC_ALL=C sed -e 's/\r$// ; 1 s/^\xef\xbb\xbf//' -i -- filename

to remove the byte order mark from the beginning of the file, if it has any, as well as convert any CR LF newlines to LF only. The LANG=C LC_ALL=C tells the shell you want the command to run in the default C locale (also known as the default POSIX locale), where the three bytes forming the Byte Order Mark are treated as bytes. The -i option to sed means in-place. If you use -i.old, then sed saves the original file as filename.old, and the new file (with the modifications, if any) as filename.

I personally like to have this as ~/bin/fix-ms; for example, as

#!/bin/dash
export LANG=C LC_ALL=C
if [ $# -gt 0 ]; then
    for FILE in "$@" ; do
        sed -e 's/\r$// ; 1 s/^\xef\xbb\xbf//' -i -- "$FILE" || exit 1
    done
else
    exec sed -e 's/\r$// ; 1 s/^\xef\xbb\xbf//'
fi

so that if I need to apply this to say all C source files and headers (my old code from the MS-DOS era, for example!), I just run

find . -name '*.[CHch]' -print0 | xargs -r0 ~/bin/ms-fix

or, if I just want to look at such a file, without modifying it, I can run

~/bin/ms-fix < filename | less

and not see the ugly <U+FEFF> in my UTF-8 terminal.

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  • Why not simply sed -e 's/\r$// ; 1 s/^\xef\xbb\xbf//' -i -- "$@"? – Stéphane Chazelas Jul 24 '17 at 14:02
  • @StéphaneChazelas: Because I want the script to exit immediately if there is an issue with a replacement, which sed -e 's/\r$// ; 1 s/^\xef\xbb\xbf//' -i -- "$@" does not do; it does return an exit code, but it processes all files listed in the argument list before exiting. – Nominal Animal Jul 24 '17 at 14:24
  • @StéphaneChazelas: The -- before the file name(s) is, of course, important: without it, file names beginning with a dash may be considered options by sed. I edited those into my answer; thank you for the reminder! – Nominal Animal Jul 24 '17 at 14:27
0

Recently I found this tiny command-line tool which adds or removes the BOM on arbitary UTF-8 encoded files: UTF BOM Utils (new link at github)

Little drawback, you can download only the plain C++ source code. You have to create the makefile (with CMake, for example) and compile it by yourself, binaries are not provided on this page.

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