Just a general usage note. I had a very difficult time solving a problem with my script, when I accidentally put one of these backticks at the beginning of a line, like so:
[lots of code]
` $URL = "blah...";
[more code]
Since the backtick is right above the tab key, I probably just fat-fingered it while indenting the code.
What made this so hard to find, was that PHP reported a parse error about 50 or so lines *below* the line containing the backtick. (There were no other backticks anywhere in my code.) And the error message was rather cryptic:
Parse error: parse error, expecting `T_STRING' or `T_VARIABLE' or `T_NUM_STRING' in /blah.php on line 446
Just something to file away in case you're pulling your hair out trying to find an error that "isn't there."
Operadores de ejecución
PHP soporta un operador de ejecución: las comillas invertidas (``). ¡Note que estas no son las comillas sencillas! PHP intentará ejecutar el contenido entre las comillas invertidas como si se tratara de un comando del shell; la salida será retornada (es decir, no será simplemente volcada como salida; puede ser asignada a una variable). El uso del operador de comillas invertidas es idéntico al de shell_exec().
<?php
$output = `ls -al`;
echo "<pre>$output</pre>";
?>Nota:
El operador de comillas invertidas se deshabilita cuando shell_exec() esta desactivado.
Nota:
A diferencia de otros lenguajes, las comillas invertidas no tienen un significa especial dentro de string entre comillas dobles.
Vea también la sección del manual sobre funciones de ejecución de programas, popen() proc_open() y Usando PHP desde la línea de comandos.
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User Contributed Notes 3 notes
robert ¶
18 years ago
ohcc at 163 dot com ¶
7 years ago
You can use variables within a pair of backticks (``).
<?php
$host = 'www.wuxiancheng.cn';
echo `ping -n 3 {$host}`;
?>
paolo.bertani ¶
2 years ago
If you want to avoid situations like the one described by @robert you may want to disable `shell_exec` and -as a consequence- the backtick operator.
To do this just edit the `php.ini` file and add `shell_exec` to the `disable_functions` setting:
; This directive allows you to disable certain functions.
; It receives a comma-delimited list of function names.
; https://php.net/disable-functions
disable_functions = "shell_exec"
Then you can still use `exec()` to run terminal commands.
