• Erlang

prefix([], _) -> true;
prefix([Ch | Rest1], [Ch | Rest2]) ->
        prefix(Rest1, Rest2);
prefix(_, _) -> false.

prefix("abc", "abcdef").

• Erlang

B = string:find(S, Prefix) =:= S.

• VB

Dim b As Boolean = s.StartsWith(prefix)

• Ada

B := Ada.Strings.Fixed.Index (S, Prefix) = S'First;

• C

bool b = !strncmp(s, prefix, sizeof(prefix)-1);

• Clojure

(def b (starts-with? s prefix))

• Cobol

IDENTIFICATION DIVISION.
PROGRAM-ID. prefix.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 BOOLEAN-B     PIC X.
   88 b-TRUE       VALUE "T".
   88 b-FALSE      VALUE "F".
PROCEDURE DIVISION.
    IF s(1:3) = prefix(1:3)
       SET b-TRUE  TO TRUE
    ELSE
       SET b-FALSE TO TRUE
    END-IF 	 	
STOP RUN.

• C++

std::string prefix = "something";
bool b = s.compare(0, prefix.size(), prefix) == 0;

• C++

bool b = s.starts_with(prefix);

• C#

bool b = s.StartsWith(prefix);

• D

b = s.startsWith(prefix);

• Dart

var b = s.startsWith(prefix);

• Elixir

String.starts_with?(s,prefix)

• Fortran

  logical :: b
  b = index (string, prefix) == 1

• Go

b := strings.HasPrefix(s, prefix)

• Haskell

b = prefix `isPrefixOf` s

• JS

var b = (s.lastIndexOf(prefix, 0) === 0);

• JS

var b = s.startsWith(prefix);

• Java

boolean b = s.startsWith(prefix);

• Kotlin

val b = s.startsWith(prefix)

• Lisp

(defun check-prefix (s prefix)
 (cond ((> (length prefix) (length s)) Nil)
       ( T ( equal prefix (subseq s 0 (length prefix ))))))

(setf b (check-prefix s prefix))

• Lua

b = string.sub(s, 1, #prefix) == prefix

• Lua

b = s:find(prefix, 1, true) == 1

• Lua

function startswith(text, prefix)
    return text:find(prefix, 1, true) == 1
end

b = startswith(s, prefix)

• Obj-C

BOOL b=[s hasPrefix:prefix];

• PHP

$b = (bool) preg_match('#^http#', $s);

• Pascal

b := pos(prefix, s) = 1;

• Perl

$b = $prefix eq substr($s,0,length($prefix));

• Python

b = s.startswith(prefix)

• Ruby

b = s.start_with?(prefix)

• Rust

let b = s.starts_with(prefix);

• Scala

val b = s.startsWith(prefix)

• Smalltalk

b := s beginsWith: prefix