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$ help if
if: if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else COMMANDS; ] fi
    The `if COMMANDS' list is executed.  If its exit status is zero, then the
    `then COMMANDS' list is executed.  Otherwise, each `elif COMMANDS' list is
    executed in turn, and if its exit status is zero, the corresponding
    `then COMMANDS' list is executed and the if command completes.  Otherwise,
    the `else COMMANDS' list is executed, if present.  The exit status of the
    entire construct is the exit status of the last command executed, or zero
    if no condition tested true.
$ help while
while: while COMMANDS; do COMMANDS; done
    Expand and execute COMMANDS as long as the final command in the
    `while' COMMANDS has an exit status of zero.
$ help [
[: [ arg... ]
    This is a synonym for the "test" builtin, but the last
    argument must be a literal `]', to match the opening `['.
[[ ... ]]: [[ expression ]]
    Returns a status of 0 or 1 depending on the evaluation of the conditional
    expression EXPRESSION.  Expressions are composed of the same primaries used
    by the `test' builtin, and may be combined using the following operators
    
        ( EXPRESSION )  Returns the value of EXPRESSION
        ! EXPRESSION    True if EXPRESSION is false; else false
        EXPR1 && EXPR2  True if both EXPR1 and EXPR2 are true; else false
        EXPR1 || EXPR2  True if either EXPR1 or EXPR2 is true; else false
    
    When the `==' and `!=' operators are used, the string to the right of the
    operator is used as a pattern and pattern matching is performed.  The
    && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
    determine the expression's value.
$