Perl Notes

File Operation Modes

The following example overwrites a file:

open(FILE, ">../myfile.txt") || die "Could not open file $!";
print FILE "I'm writing text to a file.\n";
close(FILE);

This example reads a file line by line:

open(FILE, "<../myfile.txt") || die "Could not open file $!";
while ($line=<FILE>) {
  print $line;
}
close(FILE);

As you can see, the only difference in the open statement is the operand used (> and the <) in front of the path to the file (../myfile.txt). This tells perl what mode to open the file in. Here is a small summary of other modes for the open command.:

Operand	Description
`<`	Read access only (The same as not specifying a mode.)
`>`	Write access, create if nonexistant, and overwrite existing data.
`>>`	Write access, create if nonexistant, and append to existing data.
`+<`	Read and Write only, no file creation/appending. Overwrite existing data.
`+>`	Read, Write, Create, and Truncate
`+>>`	Read, Write, Create, and Append
`\| SYSCOMMAND`	Write data to external command only.
`SYSCOMAND \|`	Read data from external command only.

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