Recipe 23.18. Reading Standard Output from a Program

23.18.1. Problem

You want to read the output from a program; for example, you want the output of a system utility such as route(8) that provides network information.

23.18.2. Solution

To read the entire contents of a program's output, use the backtick (`) operator, as in Example 23-44.

Running a program with backticks

<?php $routing_table = `/sbin/route`; ?>

To read the output incrementally, open a pipe with popen( ), as in Example 23-45.

Reading output from popen( )

<?php $ph = popen('/sbin/route','r') or die($php_errormsg); while (! feof($ph)) {     $s = fgets($ph)            or die($php_errormsg); } pclose($ph)                    or die($php_errormsg); ?>

23.18.3. Discussion

The backtick operator, which is not available in safe mode, executes a program and returns all its output as a single string. On a Linux system with 448 MB of RAM, the command $s = `/usr/bin/free`; puts the following multiline string in $s:

              total       used       free     shared    buffers     cached Mem:        448620     446384       2236          0      68568     163040 -/+ buffers/cache:     214776     233844 Swap:       136512          0     136512

If a program generates a lot of output, it is more memory efficient to read from a pipe one line at a time. If you're printing formatted data to the browser based on the output of the pipe, you can print it as you get it. Example 23-46 prints information about recent Unix system logins formatted as an HTML table. It uses the /usr/bin/last command.

Printing recent logins with popen( )

<?php // print table header print<<<_HTML_ <table> <tr>  <td>user</td><td>login port</td><td>login from</td><td>login time</td>  <td>time spent logged in</td> </tr> _HTML_; // open the pipe to /usr/bin/last $ph = popen('/usr/bin/last','r') or die($php_errormsg); while (! feof($ph)) {     $line = fgets($ph) or die($php_errormsg);     // don't process blank lines or the info line at the end     if (trim($line) && (! preg_match('/^wtmp begins/',$line))) {         $user = trim(substr($line,0,8));         $port = trim(substr($line,9,12));         $host = trim(substr($line,22,16));         $date = trim(substr($line,38,25));         $elapsed = trim(substr($line,63,10),' ()');         if ('logged in' == $elapsed) {             $elapsed = 'still logged in';             $date = substr_replace($date,'',-5);         }         print "<tr><td>$user</td><td>$port</td><td>$host</td>";         print "<td>$date</td><td>$elapsed</td></tr>\n";     } } pclose($ph) or die($php_errormsg); print '</table>'; ?>

23.18.4. See Also

Documentation on popen( ) at, pclose( ) at, the backtick operator at, and safe mode at

PHP Cookbook, 2nd Edition
PHP Cookbook: Solutions and Examples for PHP Programmers
ISBN: 0596101015
EAN: 2147483647
Year: 2006
Pages: 445

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