Working with instances
After a more comprehensive understanding of regular expressions, let's take a look at how regular expressions are used in perl,php and JavaScript.
In general, the use format of the Perl regular expressions is as follows:
Operator/regular-expression/string-to-replace/modifiers
An operator can be an M or S, representing a matching operation and a substitution operation, respectively.
In which, a regular expression is a pattern that will be matched or replaced, and can consist of any character, meta character, or locator symbol. The replacement string is a string that replaces the found pattern matching object when the S operator is used. The final parameter items are used to control different ways of matching or replacing. For example:
s/geed/good/
The first occurrence of the geed string will be found in the target object and replaced with the good. If we want to perform multiple lookup-substitution operations within the global scope of the target object, we can use the parameter "G", or s/love/lust/g.
In addition, the parameter "I" can be used if we do not need to limit the matching case form. For example
m/jewel/i
The regular expression above will match the Jewel,jewel, or Jewel, in the target object.
In Perl, a specific operator, "=~", is used to specify a matching object for a regular expression. For example:
$flag =~ s/abc/abc/
The above regular expression will replace the string ABC in the variable $flag with ABC.
Next, we add a regular expression to the Perl program to verify the validity of the user email address format. The code is as follows:
#!/usr/bin/perl
# get input
Print "What ' s your email address?\n";
$email = <STDIN>
Chomp ($email);
# Match and display result
if ($email =~/^ ([a-za-z0-9_-]) +@ ([a-za-z0-9_-]) + (\.[ A-za-z0-9_-]) +/)
{
Print ("Your email address is correct!\n");
}
Else
{
Print ("Please try again!\n");
}
If you prefer PHP, you can use the Ereg () function to perform pattern matching operations. The Ereg () function is used in the following format:
Ereg (pattern, string)
Where pattern represents the schema of the regular expression, and string is the target object that performs a find-and-replace operation. Also verify the email address, the program code written using PHP is as follows:
<?php
if (Ereg ("^ ([a-za-z0-9_-]) +@" ([a-za-z0-9_-]) + (\.[ A-za-z0-9_-]) + ", $email))
{echo "Your email address is correct!";}
Else
{echo ' please try Again! ';}
?>
Finally, let's look at JavaScript. JavaScript 1.2 has a powerful regexp () object that can be used to match regular expressions. The test () method can verify that the target object contains a match pattern and returns TRUE or false accordingly.
We can use JavaScript to write the following script to verify the validity of the email address entered by the user.
<script language= "Javascript1.2" >
<!--start hiding
function verifyaddress (obj)
{
var email = obj.email.value;
var pattern =/^ ([a-za-z0-9_-]) +@ ([a-za-z0-9_-]) + (\.[ A-za-z0-9_-]) +/;
Flag = pattern.test (email);
if (flag)
{
Alert ("Your email address is correct!");
return true;
}
Else
{
Alert ("Please try again!");
return false;
}
}
Stop hiding-->
</script>
<body>
<form onsubmit= "Return to Verifyaddress (this);" >
<input name= "Email" type= "text" >
<input type= "Submit" >
</form>
</body>
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