How can i check if a string starts with a specific word in php?

I'm trying to check if a string starts with http. How can I do this check?

$string1 = 'google.com';
$string2 = '//www.google.com';

asked May 7, 2010 at 18:43

4

PHP 8 or newer:

Use the str_starts_with function:

str_starts_with['//www.google.com', 'http']

PHP 7 or older:

Use the substr function to return a part of a string.

substr[ $string_n, 0, 4 ] === "http"

If you're trying to make sure it's not another protocol. I'd use // instead, since https would also match, and other things such as http-protocol.com.

substr[ $string_n, 0, 7 ] === "//"

And in general:

substr[$string, 0, strlen[$query]] === $query

Pikamander2

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answered May 7, 2010 at 18:46

Kendall HopkinsKendall Hopkins

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10

Use strpos[]:

if [strpos[$string2, 'http'] === 0] {
   // It starts with 'http'
}

Remember the three equals signs [===]. It will not work properly if you only use two. This is because strpos[] will return false if the needle cannot be found in the haystack.

CodeZombie

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answered May 7, 2010 at 18:45

awgyawgy

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14

There is also the strncmp[] function and strncasecmp[] function which is perfect for this situation:

if [strncmp[$string_n, "http", 4] === 0]

In general:

if [strncmp[$string_n, $prefix, strlen[$prefix]] === 0]

The advantage over the substr[] approach is that strncmp[] just does what needs to be done, without creating a temporary string.

dave

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answered May 7, 2010 at 23:26

SidSid

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4

You can use a simple regex [updated version from user viriathus as eregi is deprecated]

if [preg_match['#^http#', $url] === 1] {
    // Starts with http [case sensitive].
}

or if you want a case insensitive search

if [preg_match['#^http#i', $url] === 1] {
    // Starts with http [case insensitive].
}

Regexes allow to perform more complex tasks

if [preg_match['#^https?://#i', $url] === 1] {
    // Starts with // or // [case insensitive].
}

Performance wise, you don't need to create a new string [unlike with substr] nor parse the whole string if it doesn't start with what you want. You will have a performance penalty though the 1st time you use the regex [you need to create/compile it].

This extension maintains a global per-thread cache of compiled regular expressions [up to 4096]. //www.php.net/manual/en/intro.pcre.php

answered Dec 6, 2013 at 8:25

user276648user276648

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8

You can check if your string starts with http or https using the small function below.

function has_prefix[$string, $prefix] {
   return substr[$string, 0, strlen[$prefix]] == $prefix;
}

$url   = '//www.google.com';
echo 'the url ' . [has_prefix[$url, '//']  ? 'does' : 'does not'] . ' start with //';
echo 'the url ' . [has_prefix[$url, '//'] ? 'does' : 'does not'] . ' start with //';

Salim

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answered Jun 19, 2013 at 14:01

TURTLETURTLE

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