PHP - escape backslash doesn't work

Question

Well the title sums it up. If I do this:

fwrite($handle, 'test\r\ntest');

I get litreally that written to a file. That is:

test\r\ntest

It doesn't work for echo or any other function manipulates strings.

This became a problem when I needed to write to a printer in the serial port using ESC/POS. If I use PHP, it prints a bunch of question makrs and french characteres. With Python (plus pyserial), using the following code, works amazingly:

from __future__ import print_function
import serial

ser = serial.Serial('COM4');

ser.write('\x1b\x40');
ser.write('\x0a');
ser.write('\x0a');
ser.write('Hello there');
ser.write('\x0a');
ser.write('\x1d\x56\x42\x03');

My system: WAMP 2.4 (PHP 5.4.16, Apache 2.4.4) on Windows 7 Home Basic x64

Calimero · Accepted Answer · 2013-12-21 15:05:28Z

5

For the backslash sign to escape special characters you need to use double-quoted strings, not single-quoted ones, try these :

fwrite($handle, 'test\r\ntest'); // not working
fwrite($handle, "test\r\ntest"); // works as expected

It may be worth noting that the problem could have been skipped altogether if your data came from another source (non-php file, web form), and happens only when you hardcode your strings inside your script file. For further details, feel free to browse the relevant manual page :

http://www.php.net/manual/en/language.types.string.php

edited Dec 21, 2013 at 15:05

answered Dec 21, 2013 at 14:54

Calimero

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Ian Letourneau · Accepted Answer · 2013-12-21 14:55:29Z

4

Using a single quote will literally write your string. To use escaped characters you need to use a double quote instead :

echo "This output will \n expand";

http://www.php.net/manual/en/language.types.string.php

answered Dec 21, 2013 at 14:55

Ian Letourneau

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1 Comment

Nahuel Over a year ago

I realized that the quotes were wrong, thank you. That means the problem is not there, since it still doesn't write correctly to serial port (unlike python).

linepogl · Accepted Answer · 2013-12-21 14:54:23Z

2

Try using " instead of ' for these escape sequences:

fwrite($handle, "test\r\ntest");

answered Dec 21, 2013 at 14:54

linepogl

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