In /logs/firmware/unblob_extracted/firmware_extract/4325012-58052244.squashfs_v4_le_extract/usr/sbin/httpd-header-load line 25:

	done < $file

               ^---^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 

	done < "$file"

In /logs/firmware/unblob_extracted/firmware_extract/4325012-58052244.squashfs_v4_le_extract/usr/sbin/httpd-header-load line 37:

while header=$(g_keyfile_parser "$CUSTOMHEADER_KEYFILE" [customheaders] "$index")

                                                        ^-------------^ SC2102 (info): Ranges can only match single chars (mentioned due to duplicates).

In /logs/firmware/unblob_extracted/firmware_extract/4325012-58052244.squashfs_v4_le_extract/usr/sbin/httpd-header-load line 41:

	[ $((index++)) == 0 ] || header_names="$header_names "

                  ^-- SC3018 (warning): In POSIX sh, ++ is undefined.

                       ^-- SC3014 (warning): In POSIX sh, == in place of = is undefined.

In /logs/firmware/unblob_extracted/firmware_extract/4325012-58052244.squashfs_v4_le_extract/usr/sbin/httpd-header-load line 48:

echo $header_names

     ^-----------^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean: 

echo "$header_names"

For more information:

  https://www.shellcheck.net/wiki/SC3014 -- In POSIX sh, == in place of = is ...

  https://www.shellcheck.net/wiki/SC3018 -- In POSIX sh, ++ is undefined.

  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...