Perl | Writing to a File

A filehandle is a variable that is used to read and write to a file. This filehandle gets associated with the file.

In order to write to the file, it is opened in write mode as shown below:

open (FH, ‘>’, “filename.txt”);

If the file is existing then it truncates the old content of file with the new content. Otherwise a new file will be created and content will be added.

print() function

print() function is used to write content to a file.

Syntax: print filehandle string

Here, filehandle is associated to the file at the time of opening the file and string holds the content to be written to the file.

Example :

# Opening file Hello.txt in write mode
open (fh, ">", "Hello.txt");

# Getting the string to be written
# to the file from the user
print "Enter the content to be added\n";
$a = <>;

# Writing to the file
print fh $a;

# Closing the file
close(fh) or "Couldn't close the file";

Before Writing to File:

Executing Code to Write:

Updated File:

Here is how the program works:
Step 1: Opening file Hello.txt in write mode.
Step 2: Getting the text from the standard input keyboard.
Step 3: Writing the string stored in ‘$a’ to the file pointed by filehandle ‘fh’
Step 4: Closing the file.

Copying Content from one file to another:

Before Code Execution:
Source File:

Destination File:

Example :
Example below reads the content from the source file and writes it to destination file.

# Source File
$src = 'Source.txt';

# Destination File
$des = 'Destination.txt';

# open source file for reading
open(FHR, '<', $src);

# open destination file for writing
open(FHW, '>', $des);

print("Copying content from $src to $des\n");
while(<FHR>)
{
   print FHW $_;
}

# Closing the filehandles
close(FHR);
close(FHW);

print "File content copied successfully!\n";

Executing Code:

Updated Destination File:

Here is how the program works:-
Step 1: Opening 2 files Source.txt in read mode and Destination.txt in write mode.
Step 2: Reading the content from the FHR which is filehandle to read content while FHW is a filehandle to write content to file.
Step 3: Copying the content with the use of print function.
Step 4: Close the conn once reading file is done.

Error Handling and Error Reporting

There are two ways in which Errors can be handled

• Throw an exception if file cannot be opened (Handling an error)
• Give a warning if file cannot be opened and continue running (Error reporting)

Throw an Exception (Using Die Function)
When filehandle could not be assigned a valid file pointer at that time die gets executed printing the message and kills the current program.
Example :

# Initializing filename
$filename = 'Hello.txt';
# $filename = 'ello.txt';

# Prints an error and exits
# if file not found
open(fh, '<', $filename) or
     die "Couldn't Open file $filename";

In the above code when File exists it simply gets executed with no errors but if file doesn’t exists then it generates an error and code terminates.

Give a warning (Using warn function)
When filehandle could not be assigned a valid file pointer it just prints warning message using warn function and keeps running.
Example :

# Initializing filename
$filename = 'GFG.txt';

# Opening a file and reading content
if(open(fh, '<', $filename))
{
    while(<fh>)
    {
        print $_;
    }
}

# Executes if file not found
else
{
  warn "Couldn't Open a file $filename";
}

When File exists:

When File doesn’t exists: