Reading and Writing Files in Perl

Once you have an open file handle in Perl, you need to be able to read and write information. There are a number of different ways of reading and writing data into the file.

The <FILEHANDL> Operator

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 −

#!/usr/bin/perl
print "What is your name?\n";
$name = <STDIN>;
print "Hello $name\n";

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 −

#!/usr/bin/perl
open(DATA,"<import.txt") or die "Can't open data";
@lines = <DATA>;
close(DATA);

getc Function

The getc function returns a single character from the specified FILEHANDLE, or STDIN if none is specified −

getc FILEHANDLE
getc

If there was an error, or the filehandle is at end of file, then undef is returned instead.

read Function

The read function reads a block of information from the buffered filehandle: This function is used to read binary data from the file.

read FILEHANDLE, SCALAR, LENGTH, OFFSET
read FILEHANDLE, SCALAR, LENGTH

The length of the data read is defined by LENGTH, and the data is placed at the start of SCALAR if no OFFSET is specified. Otherwise data is placed after OFFSET bytes in SCALAR. The function returns the number of bytes read on success, zero at end of file, or undef if there was an error.

print Function

For all the different methods used for reading information from filehandles, the main function for writing information back is the print function.

print FILEHANDLE LIST
print LIST
print

The print function prints the evaluated value of LIST to FILEHANDLE, or to the current output filehandle (STDOUT by default). For example −

print "Hello World!\n";