php shell_exec() command usage_PHP tutorial

The PHP CLI SAPI allows you to develop PHP-supported shell scripts, even desktop-based scripts. In fact, the tool can be run from the PHP command line. This way, PHP developers can be as productive as Perl, AWK, Ruby, or shell programmers. This article explores the tools built into PHP to let you understand the underlying shell environment and file system in which PHP runs. PHP provides a number of functions for executing external commands, including shell_exec(), exec(), passthru(), and system(). These commands are similar but provide different interfaces for the external programs you run. All of these commands spawn a child process that runs the command or script you specify, and each child process captures the command output as it is written to standard output (stdout).

PHP CLI SAPI allows you to develop PHP supported shell scripts, even desktop-based scripts. In fact, the tool can be run from the PHP command line. This way, PHP developers can be as productive as Perl, AWK, Ruby, or shell programmers. This article explores the tools built into PHP to let you understand the underlying shell environment and file system in which PHP runs. PHP provides a number of functions for executing external commands, including shell_exec(), exec(), passthru(), and system(). These commands are similar but provide different interfaces for the external programs you run. All of these commands spawn a child process that runs the command or script you specify, and each child process captures the command output as it is written to standard output (stdout).

shell_exec()

Listing 1. Counting the number of words using backticks
Copy the code as follows:

#! /bin/sh
number_of_words=`wc -w *.txt`
echo $number_of_words

#result would be something like:
#165 readme.txt 388 results.txt 588 summary.txt
# and so on....

In your PHP script, you can run this simple command in shell_exec(), as shown in Listing 2, and get the desired results. It is assumed here that there are some text files in the same directory.

Listing 2. Running the same command in shell_exec()
Copy the code as follows:

$results = shell_exec('wc -w * .txt');
echo $results;
?>

As you can see in Figure 1, the results obtained are the same as those obtained from the shell script. This is because shell_exec() allows you to run an external program through the shell and then returns the result as a string.
Figure 1. Results of running a shell command via shell_exec()

Note that just using the trailing apostrophe operator will give you the same result, as shown below.
Listing 3. Using only the trailing apostrophe operator
Copy the code as follows:

$results = `wc -w *.txt`;
echo $results;
?>

Listing 4 shows a simpler approach.
Listing 4. A simpler method
Copy the code as follows:

echo `wc -w *.txt`;
?>

It’s important to know that a lot can be accomplished through the UNIX command line and shell scripts. For example, you can use pipes to connect commands. You can even create a shell script within it using operators and just call the shell script (with or without parameters as needed).

For example, if you only want to count the words of the first 5 text files in that directory, you can use a vertical bar (|) to connect the wc and head commands. Alternatively, you can place the output inside a pre tag to render it more beautifully in a web browser, as shown below.

Listing 5. More complex shell commands
Copy the code as follows:

$results = shell_exec('wc -w *.txt | head - 5');
echo "".$results . "";
?>

Figure 2 demonstrates the running list 5 results obtained by the script.
Figure 2. Results from shell_exec() running a more complex shell command

Later in this article, you will learn how to pass arguments to these scripts using PHP. Now you can think of this as a way to run a shell command, but remember that you can only see standard output. If an error occurs with a command or script, you won't see the standard error (stderr) unless you add it to stdout via a pipe.

Official website reference

define("__USED_CHARS__", "abcdefghijklmnopqrstuvwxyz0123456789");
define("__CASE_SENSITIVE__", true); // Use string above or use uppercase / lowercase variant

$bf = new chargen(2); // new chargen object, length 2
$bf->generate("whois"); // generate chars and call whois function

function whois($str)
{
    $domain = $str.".com";

    $retval = shell_exec("whois $domain" );

        if (eregi("no match", $retval))
                echo $domain." ist availablen";
        else
                echo $domain." is unavailablen";
}

class chargen
{
        private $chars = NULL;
        private $maxlength = NULL;

        protected $buffer = NULL;

        function generate($mycallback = false)
        {
                foreach ($this->buffer as $char)
                {
                        foreach ($this->chars as $nextchar)
                        {
                                $retval = $char.$nextchar;
                                $this->buffer[$retval] = $retval;

                                if ($mycallback && function_exists($mycallback))
                                        $mycallback($retval);
                                else
                                        echo $retval."n";
                        }
                }

                if (strlen($retval) == $this->maxlength)
                        return;

                $this->generate($mycallback);
        }

        function __construct($maxlength = 8)
        {
                $chars = array();

                $this->buffer = array();
                array_push($this->buffer, "");

                for ($i = 0; $i < strlen(__USED_CHARS__); $i++)
                {
                        $index = substr(__USED_CHARS__, $i, 1);

                        if (__CASE_SENSITIVE__)
                        {
                                $this->chars[$index] = $index;
                        }
                        else
                        {
                                $this->chars[strtolower($index)] = strtolower($index);
                                $this->chars[strtoupper($index)] = strtoupper($index);
                        }
                }

                $this->maxlength = $maxlength;
        }
}
?>

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