Perl Learning (2) File Processing

1. Read an object. If the object does not exist, an error is reported and the error cause is displayed.

open (DB, "/home/ellie/myfile") or die "Can't open file: $!\n";  

After running, the system prompts: Can't open file: no such file or Director 2. how to read and write files:

Open (FH, "<FILENAME"); # opens "FILENAME" for reading. Read
# The <; symbol is optional.



Open (FH, "> FILENAME"); # opens "FILENAME" for writing. Write
# Creates or truncates file.



Open (FH, "> FILENAME"); # opens "FILENAME" for appending. append
# Creates or appends to file.


Open (FH, "+ <FILENAME"); # opens "FILENAME" for read, then write. Write after read
Open (FH, "+> FILENAME"); # opens "FILENAME" for write, then read. First write and then read


Close (FH );

3. Open and print the file

#!/usr/bin/perl

open(FH, "<d:/readtest.txt") or die "Can't open file: $!\n";
while(<FH>){ print }

4. File Attributes

#! /Usr/bin/perl



My $ file = "D:/readtest.txt ";


# Is it readble, writeable, and executable?
Print "file is readable, writeable, and executable \ n" If-r $ file and-W _ and-X _;


# When was it last modified?
Print "file was last modified",-M $ file, "days ago. \ n ";


# Print a directory
Print "file is a directory. \ n" If-d $ file; # Is it a directory?

Because this file actually exists and is just created, but it is only a common text file, the final result is file was last modified 0.0239930555555556 days ago. if the code is print "file is readable, writeable, and executable \ n" If-r $ file and-W _ and-X _; is changed to: Print "file is readable, writeable, and executable \ n "If-r $ file and-W _; the final result is:

File is readable, writeable, and executable

File was last modified 0.0251851851851852 days ago.

 

-W _ is short for-W $ file.