I'm working with a Windows-10 computer, using a WSL.

I'm investigating a logfile, produced by NLog in a C# application. I'm expecting log entries to appear everywhere throughout the file, but I see the following:

Linux prompt> grep "geen mengcontainer" logfile.log
2023-03-07 07:25:08.7971 | Warn | ... | geen mengcontainer.
2023-03-07 07:25:09.8285 | Warn | ... | geen mengcontainer.
2023-03-07 07:25:10.8754 | Warn | ... | geen mengcontainer.
Binary file logfile.log matches

As you see, after 07:25:10, the grep stops, even though the file goes further for the rest of the day. There seems to be some character, telling grep that the file is not a textfile, but a binary file, causing grep to stop working.

Some more information about the file:

Linux prompt>file logfile.log
logfile.log: ASCII text, with CRLF line terminators

Some more information about my Linux WSL installation:

Linux prompt>uname -a
Linux ComputerName 4.4.0-19041-Microsoft
  #2311-Microsoft Tue Nov 08 17:09:00 PST 2022 
  x86_64 x86_64 x86_64 GNU/Linux

Linux prompt> cat /etc/os-release
VERSION="20.04.2 LTS (Focal Fossa)"
PRETTY_NAME="Ubuntu 20.04.2 LTS"

Some more information about my grep installation:

Linux prompt> grep --version
grep (GNU grep) 3.4

What can I do?

  • Does anybody know how to find and replace the character, which is responsible for grep to stop filtering?
  • Does anybody know which extra parameter or switch I can add to grep in order not to stop filtering?
  • Does anybody know about a grep version which does not behave like this? (Please take into account that apt update things don't work on my environment)

Thanks in advance

  • 3
    You've already gotten the answer (use -a), but consider that with a different approach you would easily find the answer yourself. You mention you're looking for a grep flag to change handling of binary files; the obvious place to look for that is man grep. But it's a long man page, and nobody wants to read it all. So, try searching it for "inary" with /inary (this catches both "Binary" and "binary"). This turns up the answer straight away.
    – amalloy
    Mar 9 at 7:54
  • @Greenonline: I disagree with the rejection of my edit: the answer starts with the idea to always use the -a switch, which is indeed a good way to handle my particular problem, hence my acceptance and upvote of the answer. To that, I have added an instruction on how to make sure that the -a switch is always used. Apparently some people don't agree with that, but you can leave it up to the answer author to decide about rejecting or approving the edit.
    – Dominique
    Mar 9 at 11:55
  • @amalloy: if you configure your pager (typically less) to make / searches case insensitive, you can just search for binary. The less option is -i, which you can put in a LESS=-i environment variable, or your ~/.lesskey. I put LESS = iMRj5X in that startup file to use a more verbose prompt, and make searching put the target line at line 5 instead of the top so I can see context, etc. I also bind , and . to prev/next file (less used to compile that init file to a binary to minimize startup time, but that's no longer a thing.) Mar 10 at 9:39

1 Answer 1


Use grep -a to force a file to always be treated as text.

The "binary file" detection is codepage-sensitive – if grep expects UTF-8 input as usual on Linux, it will actually end up detecting "ANSI" (Windows-125x, ISO 8859-x) encoded text files as binary files. Running grep under the "C" locale with LC_CTYPE=C grep or LC_ALL=C grep may also avoid this problem.

(Also, what 'file' says about the input being "ASCII" is based entirely on a quick look at the initial bytes within the file; it doesn't actually scan the entire thing, whereas 'grep' of course does.)

Usually the entire file is in the same encoding (i.e. all of it is likely to be non-UTF-8), so an easy way to find the problematic characters is to search for non-ASCII bytes (LC_ALL=C may be needed):

grep -a -P -n --color '[^\x00-\x7F]' logfile.log
perl -ne 'print "Line $.:\t$_" if /[^\0-\177]/' < logfile.log

This would also highlight the bytes in question:

perl -ne 'print "Line $.:\t$_" if s/[^\0-\177]/sprintf"\e[41m<%02X>\e[m",ord$&/ge' < logfile.log

If the file is valid UTF-8 except with some odd lines, use a similar approach to print lines that fail UTF-8 decoding:

perl -MEncode -ne 'print "Line $.:\t$_" if !eval{decode("UTF-8", $_, Encode::FB_CROAK)}' < logfile.log
  • 2
    Thanks a lot for your quick reply: using grep -a I can indeed make grep do the full filtering. Once my analysis is done, I'll have a look at the Perl commands you mentioned in order to find out what might be going wrong with my file.
    – Dominique
    Mar 8 at 9:03
  • 3
    NUL bytes might also make it detect a binary file, even in the C locale, e.g. printf 'xyz\0' |LC_ALL=C grep xyz gives "Binary file (standard input) matches" at least with the grep I have.
    – ilkkachu
    Mar 8 at 21:30
  • 2
    @Dominique That may bite you when you (accidentally) grep actual binary files. The resulting binary output may mess with your terminal and have unexpected side effects. That's a big part of the reason grep behaves like this by default. I suspect this may also be why people rejected your edit.
    – marcelm
    Mar 9 at 17:07
  • 1
    It's more that instructions for customizing shell aliases are quite out of scope for the question or answer, I think. Mar 9 at 17:41
  • 2
    It's a terrible idea to alter my "grep" in order for it to treat files always as textfiles. It means if you accidentally grep a CHROME.EXE, you'll be spammed with megabytes and megabytes of binary noise, a chunk for every byte of the Chrome binary that happens to have the value 0x61 (lowercase 'a'). If you have text files that contain binary data, they should be RARE (IOW, that default is expecting zebras), and you're better off figuring out why binary data is creeping into the log (it's always a log), then fixing whatever's doing the logging so it doesn't happen anymore.
    – FeRD
    Mar 10 at 4:32

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