The loop construct, found in nearly all procedural languages, that executes one or more instructions (the "loop body") repeatedly so long as some condition evaluates to true. In contrast to a repeat loop, the loop body will not be executed at all if the condition is false on entry to the while.
For example, in C, a while loop is written
where <expr> is any expression and <statement> is any statement, including a compound statement within braces "..".
A for loop, e.g. in the C language, extends the while loop syntax to collect pre-loop initialisation and loop-end logic into the beginning of the statement.
Perl provides the "until" loop that loops until the loop condition is true.