A FILEHANDLE is a temporary alias name given to a file that we will be using in perl script. Major functions used for this: Open (), Read (), Write (), Close ().
open (FILENAME, “< xyz.txt”);
Here the FILEHANDLE “FILENAME” will be associated with the file “xyz.txt”. This FILEHANDLE is then used to read from the file.
There are various modes of operation: read (<), write (>), append (>>), read/write [(+<) or (+>)], read/append (+>>)
open (FILE, “< abc.log”); — reads the file
open (FILE, “>abc.log”); — writes in to the file
open (FILE, “>> abc.log”); — appends the file
open (FILE, “< abc.log” or die $!); — if the file abc.log does not exist or it is not readable then the script will die with display of whatever message stored in $!
- +> –opens the file in read/write mode and also creates the file if does not exist. It also delete/truncate existing file.
Write to a File
open (FH, “> abc.txt”); — here file handle is opened in write mode
print FH $data; — content of $data will be written to the file handle FH. Here $ data can also be a scalar, a list or a hash.
close FH or die $! – here the close command may error out while trying to close a closed file. So it will die with displaying message stored in $!
Input from STDIN
<STDIN> is used for reading from the standard input in perl.
$data = <STDIN>;
Output to STDOUT
Print and printf function are used to display result in standard output.
print 2+3, “Hi There” – prints 5Hi There
STDIN and STDOUT can also be opened with other FILEHANDLE
open (FH_IN, “– “);
print FH_IN, “Standard input is opened with name: FH_IN”;
open (FH_OUT, “> – “);
print FH_OUT “Standard Output is opened with the name: FH_OUT”;
Position of FILEHANDLE
Tell () function is used to return the current position of FILEHANDLE in bytes. If not specified it assumes last line as the position.
$x = tell FILEHANDLE
Seek () function is used to position the file pointer to a specific location based on the bytes specified . This works like cut command in unix.
Syntax: seek FH, bytes, WHENCE – here WHENCE is the position of file pointer from where specified bytes of data will be fetched.
Seek FILE, 5,0 – this reads file after first 5 bytes