129

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
4

10 Answers 10

132

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

If you are using the BSD version of sed (eg macOS) then you need to have bash do the escaping:

 sed $'1s/\xef\xbb\xbf//' < orig.txt > new.txt
11
  • 4
    this may not work in a utf8 locale, but prepending a locale override to c or posix will always work.
    – hildred
    Jul 23, 2017 at 15:29
  • 3
    @hildred I've tested it with the en_US.UTF-8 locale and it worked. When will it fail?
    – m13r
    Jul 24, 2017 at 6:55
  • 2
    @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, 2017 at 16:25
  • 4
    To fix it to work with a unicode-enabled sed do LC_ALL=C sed '1s/^\xEF\xBB\xBF//'
    – Joshua
    Jul 24, 2017 at 17:41
  • 2
    @mazunki, 1s/ means only search the first line; other lines are unaffected. The ^ means only match at the start of the (first) line. \xEF\xBB\xBF is the UTF-8 BOM (escaped hex string). // means replace with nothing. I could have added 1 to the end (for 1s/^xEF\xBB\xBF//1), which would mean only match the first occurrence of the pattern on the line. But as the the search is anchored with ^, this won't make any difference. If the file doesn't have the BOM at the start of the first line, the pattern won't match, and thus no change is made.
    – CSM
    Oct 27, 2019 at 18:47
111

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
12
  • 20
    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. Jul 23, 2017 at 14:02
  • 21
    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, 2017 at 14:09
  • 2
    Is there a way of not converting the line endings and just remove the BOM with dos2unix?
    – m13r
    Jul 25, 2017 at 7:55
  • 2
    @m13r Then use the sed script in this answer. That will remove only the bom (if it exist), nothing else will be changed.
    – done
    Jul 26, 2017 at 5:51
  • 4
    @JohanMyréen yes, but it is not correct calling them UTF-8. They are not UTF-8 files. They are UTF-8-with-BOM files, which is another file format. I suppose those Windows freaks won't be happy getting ODT files callled MSOffice files :) Nov 9, 2018 at 9:47
79

Using VIM

  1. Open file in VIM:

     vi text.xml
    
  2. Remove BOM encoding:

     :set nobomb
    
  3. Save and quit:

     :wq
    

For a non-interactive solution, try the following command line:

vi -c ":set nobomb" -c ":wq" text.xml

That should remove the BOM, save the file and quit, all from the command line.

3
  • 1
    Oddly with vim 8 on a mac, I have a csv utf-8 file made by Excel and it starts with <feff>, yet :set nobomb doesn't modify or remove it.
    – dlamblin
    Oct 9, 2019 at 21:11
  • 1
    This is much faster than tail on large files.
    – user239558
    Dec 2, 2019 at 20:14
  • For multiple files: vim -c ":bufdo set nobomb|update" -c "q" * Sep 7, 2021 at 13:41
32

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

tail -c +4 withBOM.txt > withoutBOM.txt

Be aware that this chops the first 4 bytes from the file, so be sure that the file really contains the BOM before running tail.

8
  • 2
    Why 4? The BOM has 3 byte.
    – deviantfan
    Jul 23, 2017 at 17:12
  • 12
    @deviantfan Which is why you need to start at the 4th byte if you want to skip it. Jul 23, 2017 at 18:33
  • 13
    tail is using 1 based indexing?! WTF! Jul 23, 2017 at 19:31
  • 6
    @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. Jul 23, 2017 at 23:05
  • 2
    @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. Jul 24, 2017 at 6:16
7

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.

3
  • 1
    Why not simply sed -e 's/\r$// ; 1 s/^\xef\xbb\xbf//' -i -- "$@"? Jul 24, 2017 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. Jul 24, 2017 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! Jul 24, 2017 at 14:27
7

I use a vim one-liner on the regular for this:

vim --clean -c 'se nobomb|wq' filename

vim --clean -c 'bufdo se nobomb|wqa' filename1 filename2 ...
1
  • This should also be achievable using VIM's ex personality.
    – JdeBP
    Oct 7, 2020 at 9:46
2

I have a slightly different problem, and am putting this here for someone who, like me, ends up here with data full of ZERO WIDTH NO-BREAK SPACE characters (which are known as Byte Order Mark when they are the first character of the file).

I got this data by copying out of grafana query metrics field, and it had multiple (17) \xef\xbb\xbf sequences (which show up in vim as rate<feff>(<feff>node<feff>{<feff>job<feff>) in a single line with only 81 actual characters.

I modified Nominal Animal's code just slightly:

LANG=C LC_ALL=C sed -e 's/\xef\xbb\xbf//g'

And the :set nobomb thing in vim only removes the very first one in the file.

tried this:

LANG=C vim b

Then vim doesn't show them, but they are still there (even after a write...)

1

I had the same question and ended up writing a dedicated utility bom(1) for this. It's available here.

Here's the man page:

NAME
     bom -- Decode Unicode byte order mark

SYNOPSIS
     bom --strip [--expect types] [--lenient] [--prefer32] [--utf8] [file]
     bom --detect [--expect types] [--prefer32] [file]
     bom --print type
     bom --list
     bom --help
     bom --version

DESCRIPTION
     bom decodes, verifies, reports, and/or strips the byte order mark (BOM) at the
     start of the specified file, if any.

     When no file is specified, or when file is -, read standard input.

OPTIONS
     -d, --detect
             Report the detected BOM type to standard output and then exit.

             See SUPPORTED BOM TYPES for possible values.

     -e, --expect types
             Expect to find one of the specified BOM types, otherwise exit with an
             error.

             Multiple types may be specified, separated by commas.

             Specifying NONE is acceptable and matches when the file has no (sup-
             ported) BOM.

     -h, --help
             Output command line usage help.

     -l, --lenient
             Silently ignore any illegal byte sequences encountered when converting
             the remainder of the file to UTF-8.

             Without this flag, bom will exit immediately with an error if an ille-
             gal byte sequence is encountered.

             This flag has no effect unless the --utf8 flag is given.

     --list  List the supported BOM types and exit.

     -p, --print type
             Output the byte sequence corresponding to the type byte order mark.

     --prefer32
             Used to disambiguate the byte sequence FF FE 00 00, which can be
             either a UTF-32LE BOM or a UTF-16LE BOM followed by a NUL character.

             Without this flag, UTF-16LE is assumed; with this flag, UTF-32LE is
             assumed.

     -s, --strip
             Strip the BOM, if any, from the beginning of the file and output the
             remainder of the file.

     -u, --utf8
             Convert the remainder of the file to UTF-8, assuming the character
             encoding implied by the detected BOM.

             For files with no (supported) BOM, this flag has no effect and the
             remainder of the file is copied unmodified.

             For files with a UTF-8 BOM, the identity transformation is still
             applied, so (for example) illegal byte sequences will be detected.

     -v, --version
             Output program version and exit.

SUPPORTED BOM TYPES
     The supported BOM types are:

     NONE    No supported BOM was detected.

     UTF-7   A UTF-7 BOM was detected.

     UTF-8   A UTF-8 BOM was detected.

     UTF-16BE
             A UTF-16 (Big Endian) BOM was detected.

     UTF-16LE
             A UTF-16 (Little Endian) BOM was detected.

     UTF-32BE
             A UTF-32 (Big Endian) BOM was detected.

     UTF-32LE
             A UTF-32 (Little Endian) BOM was detected.

     GB18030
             A GB18030 (Chinese National Standard) BOM was detected.

EXAMPLES
     To tell what kind of byte order mark a file has:

           $ bom --detect

     To normalize files with byte order marks into UTF-8, and pass other files
     through unchanged:

           $ bom --strip --utf8

     Same as previous example, but discard illegal byte sequences instead of gener-
     ating an error:

           $ bom --strip --utf8 --lenient

     To verify a properly encoded UTF-8 or UTF-16 file with a byte-order-mark and
     output it as UTF-8:

           $ bom --strip --utf8 --expect UTF-8,UTF-16LE,UTF-16BE

     To just remove any byte order mark and get on with your life:

           $ bom --strip file

RETURN VALUES
     bom exits with one of the following values:

     0       Success.

     1       A general error occurred.

     2       The --expect flag was given but the detected BOM did not match.

     3       An illegal byte sequence was detected (and --lenient was not speci-
             fied).

SEE ALSO
     iconv(1)

     bom: Decode Unicode byte order mark, https://github.com/archiecobbs/bom.
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.

0

I know it's been a while, but since I had a slightly different issue, I'm posting so others may benefit.

My text file was randomly haunted by characters \fe\ff, luckily for me they appeared at start of the lines and the set of allowed characters is limited to alphanumeric.

The below command in vim cuts first non-alphanumeric character, but use it with caution as your set of allowed characters might vary.

:%s/^[^a-zA-Z0-9]//g

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