print() - Printing Output to File Handles

<< File Handles and Data Input/Output

<< Perl Tutorials - Herong's Tutorial Examples

This section describes various ways to use the print() function in different ways to output data to file handles.

Printing output to a file handle can be done by calling the print() function. Examples of print() function calling syntaxes:

1. Print the value of the default variable $_ to the pre-defined standard output channel:

rc = print;

2. Print the specified value to the pre-defined standard output channel:

rc = print value;

3. Print a list of values to the pre-defined standard output channel:

rc = print(list_of_values);

4. Print a list of values to the output channel represented by the file_handle with a very interesting syntax. The file handle is separated by a space character " " from the rest of the arguments:

rc = print(file_handle list_of_values);

5. Print a list of values to the output channel represented by the file_handle with a very interesting syntax. The file handle is separated by a space character " " from the rest of the arguments:

rc = print file_handle list_of_values;

In order to test the different forms of the print function, I wrote the following program, print.pl:

#- print.pl
#- Copyright (c) 1995 by Dr. Herong Yang, http://www.herongyang.com/
#
   $_ = "Starting:\n";
   print;
   print("1+1=",1+1,"\n");
   print(STDOUT "(1+2)*3=",(1+2)*3,"\n");
   $v = "OUT";
   open($v,"> out.tmp");
   print($v);
   print(OUT);
   print($v "The end.\n");
   exit;

Before you running the program, try to guess what you will get in the standard output channel, and what you will get in the output file, out.tmp:

>print.pl
Starting:
1+1=2
(1+2)*3=9
OUT

>type out.tmp
Starting:
The end.

Are you surprised about the behavior of the following 3 statements in the program?

• " print($v);" prints the value in $v to STDOUT.
• " print(OUT);" prints the value in $_ to OUT.
• " print($v "The end.\n");" prints the specified string to OUT.

Also note that \n will be printed as \r\n on Windows system. Check the size of out.tmp. You will see 21 bytes, but the total length of the two printed strings is only 19 bytes. You can also verify this by open out.tmp with a hex editor.

Sections in This Chapter

open() - Opening File Handles for Input and Output

print() - Printing Output to File Handles

<file_handle> - Reading Data from File Handles