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Re: Re: Simple file to array

by flounder99 (Friar)
on Jul 08, 2002 at 20:15 UTC ( [id://180304]=note: print w/replies, xml ) Need Help??


in reply to Re: Simple file to array
in thread Simple file to array

FoncÚ asked specifically for an explaination so I will do a little expaining of DamnDirtyApe's code. I'm sure any mistakes I make will be corrected Immediately.
open( FH, 'addys.txt' ) or die "Couldn't open file: $!" ;
This line opens the file "addys.txt" to filehandle FH. The function open will return a true value if the file open's sucessfully and a false value if it fails. If the file opens sucessfully the or will "short circuit" meaning since it already has a true value there is no need to evaluate the rest of the statement. If the open fails the die will be executed and the program will quit giving an error message. This is a pretty common way of testing that an open succeeded. You should always check the return value of an open it will usually save you a lot of debug time.
my @email_addys = <FH> ;
This line does the bulk of what you ask for. The my @email_addys creates a lexical array variable to hold the email addresses. The diamond operator ( <> ) on a filehandle reads the next line from the file. If it is being used in what is called a list context it will slurp up the whole file and return a list where each line of the file will be one of the elements of the list.
List context means that whatever it is feeding is expecting a list of items. Since we are assigning to an array variable this is a list context. If we were asigning to a scalar variable the diamond operator would only return a scalar containing the next line of the file (or undef if we were past the end of the file). Understanding context is one of the most important parts of understanding perl.
close( FH ) ;
Close the filehandle.

Notes: Each element of the @email_addys array will have a trailing newline "\n" (except maybe the last one depending on whether the last line of the file had a newline at the end.)

--

flounder

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Re: Re: Re: Simple file to array
by FoncÚ (Scribe) on Jul 09, 2002 at 12:30 UTC
    A nice explination...this and everyone else's has helped me a lot...thanks! As I understand lexical variables, they would be the same as not passing a variable back into the programme from a subroutine in, say, BASIC, right? It just remains inside whatever sub or block and isn't global? But in this case, to allow it to be global, I simply leave of the my? Just making sure I have things straight. Also...the way I had it chomp above doesn't seem to work...Can someone explain why not?

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