View Category
Files
Reading

Read the contents of a file into a string

perl
@file = read()
open(my $fh, '<', $path) or die "can't open $path: $!";
$string = do { local $/; <$fh> };
close $fh;
java
String text = FileUtils.readFileToString(new File("Solution109.java"), "UTF-8");
RandomAccessFile raf = null; byte[] buffer; String text = null;

try
{
raf = new RandomAccessFile("Solution399.java", "r");
buffer = new byte[(int)raf.length()]; raf.read(buffer);
text = new String(buffer);
}
groovy
contents = file.text

Process a file one line at a time

Open the source file to your solution and print each line in the file, prefixed by the line number, like:
1> First line of file
2> Second line of file
3> Third line of file
perl
open(my $fh, '<', $path) or die "can't open $path: $!";
$c = 1;
print $c++ . "> $_" for (<$fh>);
close $fh;
open my $fh, '<', $path or die "Can't open $path: $!";
while (<$fh>) {
print "$.> $_";
}
java
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader("Solution104.java"));
String line = null;
int lineNumber = 1;
while ((line=br.readLine())!=null) {
System.out.println(lineNumber + "> " + line);
lineNumber++;
}
} catch (IOException e) {
throw new RuntimeException(e);
} finally {
if (br!=null) {
try {
br.close();
} catch (Exception e) {
// ok
}
}
}
LineNumberReader lnr = null; PrintWriter pw = null; String line;

try
{
lnr = new LineNumberReader(new FileReader("Solution400.java"));
pw = new PrintWriter(System.out);
while ((line = lnr.readLine()) != null) pw.printf("%d> %s\n", lnr.getLineNumber(), line);
}
groovy
int count = 0
file.eachLine { line ->
println "${++count} > $line"
}
file.eachLine { line, count ->
println "${++count} > $line"
}
Writing

Write a string to a file

perl
open(my $fh, '>', $path) or die "can't open $path: $!";
print $fh "This line overwites file contents!";
close $fh;
java
FileWriter fw = null;

try
{
fw = new FileWriter("test.txt");
fw.write("This line overwites file contents!");
}
PrintWriter pw = null;

try
{
pw = new PrintWriter(new BufferedWriter(new FileWriter("test.txt")));
pw.print("This line overwites file contents!");
}
groovy
file.delete()
file << 'some text'
file.text = 'some text'

Append to a file

perl
open(my $fh, '>>', $path) or die "can't open $path: $!";
print $fh "This line is appended to the file!";
close $fh;
java
FileWriter fw = null;

try
{
fw = new FileWriter("test.txt", true);
fw.write("This line appended to file!");
}
PrintWriter pw = null;

try
{
pw = new PrintWriter(new BufferedWriter(new FileWriter("test.txt", true)));
pw.print("This line appended to file!");
}
groovy
file << 'some text'
Directories

Process each file in a directory

perl
use File::Glob;

for (<*>) {
process_file($_) if (-f);
}
java
for (File file : (new File("c:\\")).listFiles()) process(file);
groovy
dir.eachFile{ f -> process(f) }

Process each file in a directory recursively

perl
use File::Glob;

process_directory(".");

sub process_directory {
my $dir = shift;
for my $file (<$dir/*>) {
next unless (-r $file);
if (-f $file) {
process_file($file);
} elsif (-d $file) {
process_directory($file);
}
}
}
use File::Find ();

# Traverse desired filesystems
sub process_directory {
my $directory = shift;
File::Find::find({wanted => \&wanted}, $directory);
}

sub wanted {
process_file( $File::Find::name );
}
java
processDirectory(new File("c:\\"));
groovy
dir.eachFileRecurse{ f -> process(f) }