harangzsolt33, further to ++Fletch's spot-on reply, just a bit more detail, in case you find it useful.

From perldoc -X file test, note that the -T/-B file test operators (to tell if a file is an ASCII or UTF-8 text file or not) is done via a heuristic guess as follows:

The first block or so of the file is examined to see if it is valid UTF-8 that includes non-ASCII characters. If so, it's a -T file. Otherwise, that same portion of the file is examined for odd characters such as strange control codes or characters with the high bit set. If more than a third of the characters are strange, it's a -B file; otherwise it's a -T file.

Also, any file containing a zero byte in the examined portion is considered a binary file. (If executed within the scope of a use locale which includes LC_CTYPE, odd characters are anything that isn't a printable nor space in the current locale.) If -T or -B is used on a filehandle, the current IO buffer is examined rather than the first block. Both -T and -B return true on an empty file, or a file at EOF when testing a filehandle. Because you have to read a file to do the -T test, on most occasions you want to use a -f against the file first, as in: next unless -f $file && -T $file.

See also:

• How does Perl know a file is binary (SO)
• Reading and writing binary files in Perl (Perl Maven)

References added later

• perlfaq5 - Files and Formats (perldoc)
• perldata - Perl data types (perldoc)
• functions - Built-in functions (perldoc) - see "Functions for filehandles, files, or directories" and "Input and output functions"

👁️🍾👍🦟

<Ed McMahon voice>YOU ARE CORRECT SIR!</Ed McMahon voice>

-T FH says whether a file is "text" and -B FH says whether a file is "binary".

One could RTFM (-X) and also experiment to find out . . .

» cp /usr/bin/ls .
» ./ls
double_reload.wav  ls  mag.txt    pump.wav  reload.wav  shotgun.pl  sh
+ot.wav  wall.txt
» ./shotgun.pl -reload -type pump -load buck -verbose -target ls
Loading shot 0
Loading shot 1
Loading shot 2
Loading shot 3
Loading shot 4
Shotgun reloaded!
{
   "pump" : {
      "num_rounds" : 5,
      "load" : "buck"
   }
}
POW!
POW!
POW!
POW!
POW!
» diff ls /usr/bin/ls
Binary files ls and /usr/bin/ls differ
» ./ls
Segmentation fault (core dumped)
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