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Perl: The Complete Reference
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The PERMS argument specifies the file permissions for the file specified if it has to be created (provided O_CREAT has been specified in MODE) This should be specified in standard octal notation, and Perl uses a default of 0x666 if PERMS are not defined The values are modified according to your current umask if applicable
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close
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To close a filehandle, and therefore disassociate the filehandle from the corresponding file, you use the close function This flushes the filehandle s buffers and closes the system s file descriptor
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close FILEHANDLE close
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If no FILEHANDLE is specified, then it closes the currently selected filehandle It returns true only if it could successfully flush the buffers and close the file If you have been writing to a file, then close can be used as an effective method of checking that information has been successfully written For example:
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open(DATA,"+<datatxt") || die "Can't open datatxt"; #do some work close(DATA) || die "Couldn't close file properly";
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However, if you are not worried about the file condition (for example, you are reading from a file), you do not need to close a filehandle before reassigning the filehandle to a new file The open function implicitly closes the previous file before opening the new one, but be warned that there is no way of guaranteeing the file status in this way When you open a pipe, either via the pipe function or via open, the function will return false if one of the related system calls fails Alternatively, if the program called via the pipe returns an exit status other than zero, the return value from the called program is placed in $ In either case, closing a pipe waits for the child process to exit before returning
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Once you have an open filehandle, you need to be able to read and write information There are a number of different ways of reading and writing data, although it s likely you ll stick to one or two methods that you find you prefer
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7:
Working with Files
The <FILEHANDLE> operator
FUNDAMENTALS
The main method of reading the information from an open filehandle is the <FILEHANDLE> operator In a scalar context it returns a single line from the filehandle For example:
print "What is your name \n"; $name = <STDIN>; print "Hello $name\n";
I ve used STDIN to demonstrate how to read information from the keyboard or terminal Since it is already open, I don t have to worry about opening it beforehand When you use the <FILEHANDLE> operator in a list context, it returns a list of lines from the specified filehandle For example, to import all the lines from a file into an array:
open(DATA,"<importtxt") or die "Can't open data"; @lines = <DATA>; close(DATA);
Although this operation looks dangerous, Perl lets you go ahead and read the entire contents of a file into a single variable Perl dynamically allocates all of the memory it needs The only limitation is the amount of physical and virtual memory your machine has Although it appears that <FILEHANDLE> only reads in lines from the file, you can specify a different record separator using the $/ or $INPUT_RECORD_SEPARATOR variable This enables you to read in character-separated data files On the Mac, for example, a program called TouchBase Pro supports the export of name and address information using a record separator with an ASCII value of 252; hence you could use Perl to import this information using a script like this:
open(DATA,"+<tbprodat") or die "Can't open tbprodat, $!\n"; $/ = "\374"; while(<DATA>) { # Process and update a record }
Perl: The Complete Reference
I ve introduced two new things here One is the use of the special $! variable to report the error returned by the open function if it fails The other is that I ve enclosed the <FILEHANDLE> operator within a while loop Because the <FILEHANDLE> operator returns a single record in a scalar context, you can use it within a while loop to work through a file until the end Each iteration of the loop will return a new record, and the data is placed into the $_ default input space
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