PHP Files Reading Standard Output from a Program

PHP Files

Reading Standard Output from a Program

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.

Solution

To read the entire contents of a program’s output, use the backtick (`) operator:

       $routing_table = `/sbin/route`;

To read the output incrementally, open a pipe with popen():

       $ph = popen('/sbin/route','r') or die($php_errormsg);

       while (! feof($ph)) {

            $s = fgets($ph)                      or die($php_errormsg);

       }

       pclose($ph)                                 or die($php_errormsg);

Discussion

The backtick operator executes a program and returns all its output as a single string. On a Linux system with 1.6 GB of RAM, the command $s = /usr/bin/free; puts the following multiline string in $s:

                              total               used                free       shared         buffers          cached

     Mem:      16471704     15488260         983444                 0        627820     12076120

     -/+ buffers/cache:        2784320     13687384

     Swap:                    0                     0                     0

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.

This example prints information about recent Unix system logins formatted as an HTML table. It uses the /usr/bin/last command:

       // 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>';