How to determine if Git handles a file as binary or as text?

Question

I know that Git somehow automatically detects if a file is binary or text and that .gitattributes can be used to set this manually if needed. But is there also a way to ask Git how it treats a file?

So let's say I have a Git repository with two files in it: An ascii.dat file containing plain-text and a binary.dat file containing random binary stuff. Git handles the first .dat file as text and the secondary file as binary. Now I want to write a Git web front end which has a viewer for text files and a special viewer for binary files (displaying a hex dump for example). Sure, I could implement my own text/binary check but it would be more useful if the viewer relies on the information how Git handles these files.

So how can I ask Git if it treats a file as text or binary?

Answer 1

builtin_diff()¹ calls diff_filespec_is_binary() which calls buffer_is_binary() which checks for any occurrence of a zero byte (NUL “character”) in the first 8000 bytes (or the entire length if shorter).

I do not see that this “is it binary?” test is explicitly exposed in any command though.

git merge-file directly uses buffer_is_binary(), so you may be able to make use of it:

git merge-file /dev/null /dev/null file-to-test

It seems to produce the error message like error: Cannot merge binary files: file-to-test and yields an exit status of 255 when given a binary file. I am not sure I would want to rely on this behavior though.

Maybe git diff --numstat would be more reliable:

isBinary() {
    p=$(printf '%s\t-\t' -)
    t=$(git diff --no-index --numstat /dev/null "$1")
    case "$t" in "$p"*) return 0 ;; esac
    return 1
}
isBinary file-to-test && echo binary || echo not binary

For binary files, the --numstat output should start with - TAB - TAB, so we just test for that.

---

¹builtin_diff() has strings like Binary files %s and %s differ that should be familiar.

Answer 2

git grep -I --name-only --untracked -e . -- ascii.dat binary.dat ...

will return the names of files that git interprets as text files.

The trick here is in these two git grep parameters:

• -I: Don’t match the pattern in binary files.
• -e .: Regular expression match any character in the file

You can use wildcards e.g.

git grep -I --name-only --untracked -e . -- *.ps1

Answer 3

I don't like this answer, but you can parse the output of git-diff-tree to see if it is binary. For example:

git diff-tree -p 4b825dc642cb6eb9a060e54bf8d69288fbee4904 HEAD -- MegaCli 
diff --git a/megaraid/MegaCli b/megaraid/MegaCli
new file mode 100755
index 0000000..7f0e997
Binary files /dev/null and b/megaraid/MegaCli differ

as opposed to:

git diff-tree -p 4b825dc642cb6eb9a060e54bf8d69288fbee4904 HEAD -- megamgr
diff --git a/megaraid/megamgr b/megaraid/megamgr
new file mode 100755
index 0000000..50fd8a1
--- /dev/null
+++ b/megaraid/megamgr
@@ -0,0 +1,78 @@
+#!/bin/sh
[…]

Oh, and BTW, 4b825d… is a magic SHA which represents the empty tree (it is the SHA for an empty tree, but git is specially aware of this magic).

Answer 4

Use git check-attr --all.

This works regardless of if the file has been staged/committed or not.

Tested on git version 2.30.2.

Assuming you have this in .gitattributes.

package-lock.json binary

There is this output.

git check-attr --all package-lock.json 
package-lock.json: binary: set
package-lock.json: diff: unset
package-lock.json: merge: unset
package-lock.json: text: unset

For normal files, there is no output.

git check-attr --all package.json

Answer 5

# considered binary (or with bare CR) file
git ls-files --eol | grep -E '^(i/-text)'

# files that do not have any line-ending characters (including empty files) - unlikely that this is a true binary file ?
git ls-files --eol | grep -E '^(i/none)'

#                                                        via experimentation
#                                                      ------------------------
#    "-text"        binary (or with bare CR) file     : not    auto-normalized
#    "none"         text file without any EOL         : not    auto-normalized
#    "lf"           text file with LF                 : is     auto-normalized when gitattributes text=auto
#    "crlf"         text file with CRLF               : is     auto-normalized when gitattributes text=auto
#    "mixed"        text file with mixed line endings : is     auto-normalized when gitattributes text=auto
#                   (LF or CRLF, but not bare CR)

Source: https://git-scm.com/docs/git-ls-files#Documentation/git-ls-files.txt---eol https://github.com/git/git/commit/a7630bd4274a0dff7cff8b92de3d3f064e321359

Oh by the way: be careful with setting the .gitattributes text attribute e.g. *.abc text. Because in that case all files with *.abc will be normalized, even if they are binary (internal CRLF found in the binary would be normalized to LF). This is different from the auto behaviour.

Answer 6

At the risk of getting slapped for poor code quality, I'm listing a C utility, is_binary, built around the original buffer_is_binary() routine in the Git source. Please see internal comments for how to build and run. Easily modifyable:

/***********************************************************
 * is_binary.c 
 *
 * Usage: is_binary <pathname>
 *   Returns a 1 if a binary; return a 0 if non-binary
 * 
 * Thanks to Git and Stackoverflow developers for helping with these routines:
 * - the buffer_is_binary() routine from the xdiff-interface.c module 
 *   in git source code.
 * - the read-a-filename-from-stdin route
 * - the read-a-file-into-memory (fill_buffer()) routine
 *
 * To build:
 *    % gcc is_binary.c -o is_binary
 *
 * To build debuggable (to push a few messages to stdout):
 *    % gcc -DDEBUG=1 ./is_binary.c -o is_binary
 *
 * BUGS:
 *  Doesn't work with piped input, like 
 *    % cat foo.tar | is_binary 
 *  Claims that zero input is binary. Actually, 
 *  what should it be?
 *
 * Revision 1.4
 *
 * Tue Sep 12 09:01:33 EDT 2017
***********************************************************/
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

#define MAX_PATH_LENGTH 200
#define FIRST_FEW_BYTES 8000

/* global, unfortunately */
char *source_blob_buffer;

/* From: https://stackoverflow.com/questions/14002954/c-programming-how-to-read-the-whole-file-contents-into-a-buffer */

/* From: https://stackoverflow.com/questions/1563882/reading-a-file-name-from-piped-command */

/* From: https://stackoverflow.com/questions/6119956/how-to-determine-if-git-handles-a-file-as-binary-or-as-text
*/

/* The key routine in this function is from libc: void *memchr(const void *s, int c, size_t n); */
/* Checks for any occurrence of a zero byte (NUL character) in the first 8000 bytes (or the entire length if shorter). */

int buffer_is_binary(const char *ptr, unsigned long size)
{
  if (FIRST_FEW_BYTES < size)
    size = FIRST_FEW_BYTES;
    /* printf("buff = %s.\n", ptr); */
  return !!memchr(ptr, 0, size);
}
int fill_buffer(FILE * file_object_pointer) {
  fseek(file_object_pointer, 0, SEEK_END);
  long fsize = ftell(file_object_pointer);
  fseek(file_object_pointer, 0, SEEK_SET);  //same as rewind(f);
  source_blob_buffer = malloc(fsize + 1);
  fread(source_blob_buffer, fsize, 1, file_object_pointer);
  fclose(file_object_pointer);
  source_blob_buffer[fsize] = 0;
  return (fsize + 1);
}
int main(int argc, char *argv[]) {

  char pathname[MAX_PATH_LENGTH];
  FILE *file_object_pointer;

  if (argc == 1) {
    file_object_pointer = stdin;
  } else {
    strcpy(pathname,argv[1]);
#ifdef DEBUG
    printf("pathname=%s.\n", pathname); 
#endif 
    file_object_pointer = fopen (pathname, "rb");
    if (file_object_pointer == NULL) {
      printf ("I'm sorry, Dave, I can't do that--");
      printf ("open the file '%s', that is.\n", pathname);
      exit(3);
    }
  }
  if (!file_object_pointer) {
    printf("Not a file nor a pipe--sorry.\n");
    exit (4);
  }
  int fsize = fill_buffer(file_object_pointer);
  int result = buffer_is_binary(source_blob_buffer, fsize - 2);

#ifdef DEBUG
  if (result == 1) {
    printf ("%s %d\n", pathname, fsize - 1);
  }
  else {
    printf ("File '%s' is NON-BINARY; size is %d bytes.\n", pathname, fsize - 1); 
  }
#endif
  exit(result);
  /* easy check -- 'echo $?' after running */
}

Answer 7

@bonh gave a working answer in a comment

git diff --numstat 4b825dc642cb6eb9a060e54bf8d69288fbee4904 HEAD -- | grep "^-" | cut -f 3

It shows all files which git interprets as binaries.