How to check if the file is a binary file and read all the files which are not?

Question

How can I know if a file is a binary file?

For example, compiled c file.

I want to read all files from some directory, but I want ignore binary files.

Answer 1

cat+grep

Assuming binary means the file containing NULL characters, this shell command can help:

(cat -v file.bin | grep -q "\^@") && echo Binary || echo Text

or:

grep -q "\^@" <(cat -v file.bin) && echo Binary

This is the workaround for grep -q "\x00", which works for BSD grep, but not for GNU version.

Basically -v for cat converts all non-printing characters so they are visible in form of control characters, for example:

$ printf "\x00\x00" | hexdump -C
00000000  00 00                                             |..|
$ printf "\x00\x00" | cat -v
^@^@
$ printf "\x00\x00" | cat -v | hexdump -C
00000000  5e 40 5e 40                                       |^@^@|

where ^@ characters represent NULL character. So once these control characters are found, we assume the file is binary.

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The disadvantage of above method is that it could generate false positives when characters are not representing control characters. For example:

$ printf "\x00\x00^@^@" | cat -v | hexdump -C
00000000  5e 40 5e 40 5e 40 5e 40                           |^@^@^@^@|

See also: How do I grep for all non-ASCII characters.