This article covers how one can write PHP
scripts that exceed the maximum execution time, and thus create scripts
which will send mass emails, backup data, transfer via FTP, and much
more.
Command Line Scripting in PHP
Introduction
PHP is a great language to develop web applications rapidly and
economically. Many of us know this. But what many of us were unaware of
is that PHP can also be run as a command line script like c, c++, java,
etc. Questions may arise why do we need to run PHP on the command line?
After all, we just need to create websites with PHP, HTML, Graphics and
JavaScript.
Why PHP Command Line Scripting needed?
Apart
from building web applications and websites, there are many other tasks
that need to be run on the background in the web server. Most of these
kinds of tasks may take a few minutes to many hours to complete.
For
example, sending a bulk newsletter email to all the subscribers in a
mailing list. Can’t we do this in normal PHP through web scripting?
Yes, we can do this through normal web scripting. However, this would
work well only when there are a few hundreds of subscribers. What if
there were a few thousands of subscribers? Usually, any web script
would have only a few minutes to execute. This time period is known as
maximum execution time. After which, the web server will terminate the
web script abnormally.
By default, this maximum execution
time would be set as 5 minutes and it may vary depending upon the
server settings. In this case, our web script would be able to send
only few hundreds of emails within the given time limit. So is it not
possible to develop a bulk email sending application in PHP? Yes, here
comes the PHP Command Line Scripting.
Unlike web scripts,
Command line scripts doesn’t have any maximum execution time limit and
they can run as long as they can, unless until the server shuts down.
Using command line scripting, we can accomplish many time consuming
tasks like taking backup of entire website and databases, transferring
files to another server through ftp, and many more.
A Simple Command Line Script
How
to write a command line script in PHP? Will it be as easy as creating a
web script? Yes, we can create command line PHP script as we do for web
script, but with few little tweaks. We won’t be using any kind of html
tags in a command line scripting, as the output is not going to be
rendered in a web browser, but displayed in the DOS prompt / Shell
prompt. Don’t ever try to use <BR> tag for inserting new line in
the command line scripting ;). Instead use \n to output the new line.
Let us start with a small command line script to output “Hello World”.
<?php
print "Hello World!";
?>
Filename: helloworld.php
You can execute this script by typing the following in your command prompt or shell prmopt:
php helloworld.php
Input / Output Streams
Instead of using print or echo for output, we can use the standard
output stream defined in CLI version of the PHP. Following are the
three IO streams in PHP with which we can interact the same way as we
do with a file.
php://stdin (read)
php://stdout (write)
php://stderr (write)
These streams are defined as constants namely STDIN, STDOUT AND STDERR from PHP 4.3.0+ CLI version.
Now we rewrite the helloworld.php to use STDOUT.
<?php
fwrite(STDOUT, "Hello World!");
?>
So these streams are treated as files and we can use normal file
functions like fopen(), fread(), fwrite() to interact with these
streams.
To get input from the end users, we can use STDIN with fgets(), fread(), fscanf() or fgetc().
For example, we would write a small script that get the name of the user and output “Welcome <username>”.
<?php
fwrite(STDOUT, “Please enter your name\n”);
$name = fgets(STDIN);
fwrite(STDOUT, "Welcome $name");
?>
The third stream STDERR is used to separate the error message from normal output.
For example, the following script open a file and read it contents and
close the file. An error handler is also defined to write the errors to
the STDERR stream.
<?php
set_error_handler("ErrorHandler");
function ErrorHandler($errno, $errstr, $errfile, $errline)
{
fwrite(STDERR,"$errstr in $errfile on $errline\n");
}
$fp = fopen("demo.txt","r");
$str = fread($fp,filesize("demo.txt"));
fclose($fp);
fwrite(STDOUT, "Task completed successfully!");
?>
If the file “demo.txt” doesn’t exists, the following error messages will be displayed.
fopen(demo.txt): failed to open stream: No such file or directory in D:\demo\tmp\error.php on 10
filesize(): stat failed for demo.txt in D:\demo\tmp\error.php on 11
fread(): supplied argument is not a valid stream resource in D:\demo\tmp\error.php on 11
fclose(): supplied argument is not a valid stream resource in D:\demo\tmp\error.php on 12
Task completed successfully!
To avoid displaying of errors to the end user, we can pipe the output from the script as follows,
php error.php 2> error.log
Now, the user would see only the following message,
Task completed successfully!
The
errors would be logged into a file named “error.log” in the directory
where the script was executed. The number 2 is the command line handle
used to identify STDERR. Note that 1 is handle for STDOUT. Using the
> symbol from the command line, we can direct output to a particular
location.
Finish Up
Now
we have an idea on the basics of PHP Command Line Scripting. Though
this article is a small introduction to PHP Command Line Scripting,
hope it would have created a tiny spark for those who were unaware of
Command Line Scripting in PHP. Wishing these tiny sparks to be ignited
to become a flame.
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