5

I run 

grep -b --byte-offset 'EXTH' Agent_of_Change.mobi

but I only get "Binary file Agent_of_Change.mobi matches". How can I get the bytes offset instead?

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2 Answers 2

Reset to default
7

grep would, by default, only returns matches for binary files.

You would need to tell grep to treat binary files as text.

grep -a -b 'EXTH' Agent_of_Change.mobi

However, grep warns you of the possible consequences:

          option.  If TYPE is text, grep processes a binary file as if  it
          were  text;  this is equivalent to the -a option.  Warning: grep
          --binary-files=text might output binary garbage, which can  have
          nasty  side  effects  if  the  output  is  a terminal and if the
          terminal driver interprets some of it as commands.
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8
  • hi, I still don't get the output I need. -a gives no output. -o and -b doesn't change the output (specified in the question). Commented Apr 3, 2014 at 12:46
  • @Patrick Did you try strings yourfile | grep searchstring? If that doesn't produce an output, chances are that grep wouldn't either. Commented Apr 3, 2014 at 12:49
  • Yes, it gives me the output Commented Apr 3, 2014 at 12:56
  • @Patrick In that event, grep should as well. Don't use -o (in case you are). grep -a -b searchstring file | cut -d: -f1 should give you the offset that you are looking for. Commented Apr 3, 2014 at 12:59
  • grep EXTH Agent_of_Change.mobi gives the correct output ("Binary file .. matches"). Commented Apr 3, 2014 at 13:00
4

Add -a to force printing of matches even if they don't seem printable.

Add -o and it'll only print the "EXTH" instead of the line. That also changes the byte offset - it'll print the offset of the "EXTH" instead of the offset of the beginning of the line containing the "EXTH". If the file isn't actually made of lines, this will be an improvement!

Or use perl -n0777e 'print pos()-length($&),"\n" while /EXTH/g' to replace your GNU grep dependency with a dependency on something more universal... (Warning: slurps whole file into memory, may be unpleasant for large files)

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12
  • Does grep load all file in memory as well? Commented Apr 3, 2014 at 12:44
  • grep works on one line at a time, so it doesn't load the whole file but can load some big chunks if the input isn't text. Commented Apr 3, 2014 at 12:45
  • I've tried grep -o --byte-offset... to get the offset of the exact word (this is what I need), but i get no output. (The word is there I'm sure). Commented Apr 3, 2014 at 12:47
  • Is maybe some encoding issue related? It is MOBI e-book file. It is a binary file, with some text content here and there Commented Apr 3, 2014 at 12:47
  • 1
    +1 Perl method is excellent for recent OS X which includes grep 2.5.1, which has a bug that returns always 0 for --byte-offset. I subtracted length($matchString) rather than 1 to get the offset at the start of string rather than end. Commented Jan 31, 2016 at 13:28

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