# 1.29 if

    if <criterion> <code>
    { else if <criterion> <code> }
    [ else                <code> ]

The `if` command allows conditional execution of blocks of commands. The code enclosed in braces following the `if` statement is executed if, and only if, the `criterion` is satisfied. An arbitrary number of subsequent `else if` statements can optionally follow the initial `if` statement; these have their own criteria for execution which are only considered if all of the previous criteria have tested false – i.e. if none of the previous command blocks have been executed. A final optional `else` statement can be provided; the block of commands which follows it are executed only if none of the preceding criteria have tested true. The following example illustrates a chain of `else if` clauses:

    if (x==2)
     {
      print "x is two!"
     } else if (x==3) {
      print "x is three!"
     } else if (x>3) {
      print "x is greater than three!"
     } else {
      x=2
      print "x didn't used to be two, but it is now!"
     }