This is how you would write it as a C-style for loop:

for (my $i=0; $i <= $#people; $i++) {
    if($people[$i]{'ident'} =~ /^1[014689]*7[014689]*5[014689]*3[01468
+9]*2[014689]*$/) {
          mywrite($people[$i]);  #my print function
          
    }
}
[download]

Comments:

• @people is an array, and $people[$i] is the element with index $i in that array. The foreach version of the loop automatically maps the current array element to a new variable ($guest in this case) which is nicer to type and read than $people[$i], which is why that kind of loop is usually preferable.
  
  
• $#people is the correct syntax for referring to the last index of the @people array. The length function is only used to get the length of a string, not the number of elements in an array.

In any case, I strongly recommend that you carefully read through the whole perlintro page (and especially the "Perl variable types" section); it will make learning Perl much easier than trying to figure out the basics by trial-and-error. After that, perlreftut makes for good further reading.

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Update: Fixed link; thanks taint!