Perl | Opening and Reading a File

Last Updated : 26 Feb, 2019

A filehandle is an internal Perl structure that associates a physical file with a name. All filehandles have read/write access, so once filehandle is attached to a file reading/writing can be done. However, the mode in which file handle is opened is to be specified while associating a filehandle.

Opening a File

Open function is used to open a new file or an existing file.

Syntax: open FILEHANDLE, VAR

Here FILEHANDLE is the handle returned by the open function and VAR is the expression having file name and mode of opening the file. The table given below shows the modes in which file can be opened and access to various operations.

Mode Description

r or < Read Only Access

w or > Creates, Writes, and Truncates

a or >> Writes, Appends, and Creates

r+ or +< Reads and Writes

w+ or +> Reads, Writes, Creates, and Truncates

a+ or +>> Reads, Writes, Appends, and Creates

Reading a file

Once a FILEHANDLE is assigned a file, various operations like reading, writing and appending can be done. There are a number of different ways of reading a file.

Using a File Handle Operator
Using getc function
Using read function

The FileHandle Operator The main method of reading the information from an open filehandle is using the operator < >. When < > operator is used in a list context, it returns a list of lines from the specified filehandle. The example below reads one line from the file and stores it in the scalar. Let the content of file "GFG.txt" is as given below:
```
  GeeksforGeeks  Hello Geek  Geek a revolution  Geeks are the best  
```
Example: GFG.pl
Perl
# Opening the file open(fh, "GFG.txt") or die "File '$filename' can't be opened"; # Reading First line from the file $firstline = <fh>; print "$firstline\n";
Output :
getc Function The getc function returns a single character from the specified FILEHANDLE, or STDIN if none is specified
Syntax: getc FILEHANDLE
Perl
# Opening the file open(fh, "GFG.txt") or die "File '$filename' can't be opened"; # Reading First char from the file $firstchar = getc(fh); print "$firstchar\n";
Output: If there was an error or the filehandle is at end of the file, then it returns undef.
read Function The read function is used to read binary data from a file using filehandle.
Syntax read FILEHANDLE, SCALAR, LENGTH, OFFSET read FILEHANDLE, SCALAR, LENGTH
Here, LENGTH represents the length of data to be read and the data is placed at the start of SCALAR if no OFFSET is specified. Otherwise, data is placed after bytes of OFFSET in SCALAR. On the success of file reading, the function returns the number of bytes read, zero at end of file, or undef if there was an error.

Reading Multiple line at a time

Example: File.pl

Perl

# Opening the file open(FH, "GFG.txt")or die "Sorry!! couldn't open"; print "Reading file \n";  # Reading the file till FH reaches EOF while(<FH>) {     # Printing one line at a time     print $_; } close;