How to check if a string starts with in PHP

Question

Example  I have a  variable     foo   and I want to make absolutely sure that  variable does not start with an underscore      How can I do that in PHP  Is there some access to the char array behind the string

User · Answer

variable 0           How does it work   In PHP you can get particular character of a string with array index notation   variable 0  is the first character of a string  if  variable is a string

User · Answer

You might check out the substr function in php and grab the first character that way   http   php net manual en function substr php  if  substr   abcdef   0  1

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Since someone mentioned efficiency  I ve benchmarked the functions given so far out of curiosity   function startsWith1  str   char        return strpos  str   char      0    function startsWith2  str   char        return stripos  str   char      0    function startsWith3  str   char        return substr  str  0  1       char    function startsWith4  str   char       return  str 0       char    function startsWith5  str   char       return  bool  preg match         char         str     function startsWith6  str   char        if  is null  encoding    encoding   mb internal encoding        return mb substr  str  0  mb strlen  char   encoding    encoding       char      Here are the results on my average DualCore machine with 100 000 runs each     Testing   string  startsWith1 took 0 385906934738 startsWith2 took 0 457293987274 startsWith3 took 0 412894964218 startsWith4 took 0 366240024567  lt -- fastest startsWith5 took 0 642996072769 startsWith6 took 1 39859509468     Tested  string  startsWith1 took 0 384965896606 startsWith2 took 0 445554971695 startsWith3 took 0 42377281189 startsWith4 took 0 373164176941  lt -- fastest startsWith5 took 0 630424022675 startsWith6 took 1 40699005127     Tested 1000 char random string  a-z0-9  startsWith1 took 0 430691003799 startsWith2 took 4 447286129 startsWith3 took 0 413349866867 startsWith4 took 0 368592977524  lt -- fastest startsWith5 took 0 627470016479 startsWith6 took 1 40957403183     Tested 1000 char random string  a-z0-9  with     prefix startsWith1 took 0 384054899216 startsWith2 took 4 41522812843 startsWith3 took 0 408898115158 startsWith4 took 0 363884925842  lt -- fastest startsWith5 took 0 638479948044 startsWith6 took 1 41304707527   As you can see  treating the haystack as array to find out the char at the first position is always the fastest solution  It is also always performing at equal speed  regardless of string length  Using strpos is faster than substr for short strings but slower for long strings  when the string does not start with the prefix  The difference is irrelevant though  stripos is incredibly slow with long strings  preg match performs mostly the same regardless of string length  but is only mediocre in speed  The mb substr solution performs worst  while probably being more reliable though   Given that these numbers are for 100 000 runs  it should be obvious that we are talking about 0 0000x seconds per call  Picking one over the other for efficiency is a worthless micro-optimization  unless your app is doing startsWith checking for a living

User · Answer

function starts with  s   prefix          returns a bool     return strpos  s   prefix      0     starts with  variable

User · Answer

This is the most simple answer where you are not concerned about performance   if  strpos  string           0          code     If strpos returns 0 it means that what you were looking for begins at character 0  the start of the string   It is documented thoroughly here  http   uk3 php net manual en function strpos php   PS  string 0          is the best answer

User · Answer

Here   s a better starts with function   function mb startsWith  str   prefix   encoding null        if  is null  encoding    encoding   mb internal encoding        return mb substr  str  0  mb strlen  prefix   encoding    encoding       prefix

User · Answer

To build on pinusnegra s answer  and in response to Gumbo s comment on that answer   function has leading underscore  string         return  string 0                Running on PHP 5 3 0  the following works and returns the expected value  even without checking if the string is at least 1 character in length   echo has leading underscore   somestring         echo has leading underscore  somestring         echo has leading underscore           echo has leading underscore null        echo has leading underscore false        echo has leading underscore 0        echo has leading underscore array   foo    bar            output  true  false  false  false  false  false  false       I don t know how other versions of PHP will react  but if they all work  then this method is probably more efficient than the substr route

[php] How to check if a string starts with "_" in PHP?

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