Re: [bug-gawk] The best way to test the first n character in a file

[Stephane Chazelas]

2019-09-18 11:35:15 -0500, Peng Yu:
[...]
> I want to test if the first n character of a binary file equals some
> given string. I am not sure if awk is good at this. It seems that
> `head` plus shell code should be easier. Is there a good way to do so
> in awk? Thanks.
[...]

There's a bit of a contradiction in that statement, unless you
meant "byte" instead of "character". binary file usually means
non-text files, so where bytes (or sequence of bytes) are not
meant to be interpreted as characters.

With GNU awk, you can do:

LC_ALL=C gawk '
  BEGIN {
    bytesequence="\x7f" "ELF"
    RS = ".{" length(bytesequence) "}"
  }
  {
    if (RT == bytesequence) print FILENAME" is an ELF file"
    nextfile
  }' /bin/ls /bin/zgrep

-- 
Stephane