ruby文件操作

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1 检测文件是否存在及其大小

FileTest的 exist?方法可以检测一个文件是否存在:

flag = FileTest::exist?("LochNessMonster")
flag = FileTest::exists?("UFO")
# exists? is a synonym for exist?

flag = FileTest::exist?("LochNessMonster")
flag = FileTest::exists?("UFO")
# exists? is a synonym for exist?

如果我们想要知道文件是否有内容，可以使用File::Stat的zero? 方法:

flag = File.new("somefile").stat.zero?

flag = File.new("somefile").stat.zero?

这个将会返回true，这是因为在ruby中0也是true,nil才是false.

所以我们可以使用size?方法:

if File.new("myfile").stat.size?
  puts "The file has contents."
else
  puts "The file is empty."
end

if File.new("myfile").stat.size?
  puts "The file has contents."
else
  puts "The file is empty."
end

FileTest模块里面也有zero? 和size?方法:

flag1 = FileTest::zero?("file1")
flag2 = FileTest::size?("file2")

flag1 = FileTest::zero?("file1")
flag2 = FileTest::size?("file2")

这里还有一个size方法:

size1 = File.size("file1")
size2 = File.stat("file2").size

size1 = File.size("file1")
size2 = File.stat("file2").size

2 检测特殊文件属性

这边要注意，File类mix了FIleTest模块，并且FileTest模块和File::Stat模块功能上也有很多重复.

unix/linux有面向字符和面向块的设备。FileTest的方法blockdev?和chardev?可以进行测试:

flag1 = FileTest::chardev?("/dev/hdisk0")  # false
flag2 = FileTest::blockdev?("/dev/hdisk0") # true

flag1 = FileTest::chardev?("/dev/hdisk0")  # false
flag2 = FileTest::blockdev?("/dev/hdisk0") # true

有时我们想要知道一个流是否联系到了终端，这时我们可以使用IO类的tty?方法:

flag1 = STDIN.tty?                   # true
flag2 = File.new("diskfile").isatty  # false

flag1 = STDIN.tty?                   # true
flag2 = File.new("diskfile").isatty  # false

一个流可以是一个管道，或者一个socket:

flag1 = FileTest::pipe?(myfile)
flag2 = FileTest::socket?(myfile)

flag1 = FileTest::pipe?(myfile)
flag2 = FileTest::socket?(myfile)

要区分目录和普通文件我们这样使用：

file1 = File.new("/tmp")
file2 = File.new("/tmp/myfile")
test1 = file1.directory?          # true
test2 = file1.file?               # false
test3 = file2.directory?          # false
test4 = file2.file?               # true

file1 = File.new("/tmp")
file2 = File.new("/tmp/myfile")
test1 = file1.directory?          # true
test2 = file1.file?               # false
test3 = file2.directory?          # false
test4 = file2.file?               # true

File还有一个类方法ftype，他将返回流的类型.他也在File::Stat里面,只不过是实例方法.它的返回值可能是下面的字符

串(file、directory、blockSpecial、characterSpecial、fifo、link或socket).

this_kind = File.ftype("/dev/hdisk0")     # "blockSpecial"
that_kind = File.new("/tmp").stat.ftype   # "directory"

this_kind = File.ftype("/dev/hdisk0")     # "blockSpecial"
that_kind = File.new("/tmp").stat.ftype   # "directory"

要测试一个文件是否为另一个文件的链接，可以使用FileTest的symlink?方法，要计算链接数量，可以使用nlink方法：

File.symlink("yourfile","myfile")           # Make a link
is_sym = FileTest::symlink?("myfile")       # true
hard_count = File.new("myfile").stat.nlink  # 0

File.symlink("yourfile","myfile")           # Make a link
is_sym = FileTest::symlink?("myfile")       # true
hard_count = File.new("myfile").stat.nlink  # 0

3 使用管道

ruby中使用IO.popen打开管道:

check = IO.popen("spell","r+")
check.puts("'T was brillig, and the slithy toves")
check.puts("Did gyre and gimble in the wabe.")
check.close_write
list = check.readlines
list.collect! { |x| x.chomp }
# list is now %w[brillig gimble gyre slithy toves wabe]

check = IO.popen("spell","r+")
check.puts("'T was brillig, and the slithy toves")
check.puts("Did gyre and gimble in the wabe.")
check.close_write
list = check.readlines
list.collect! { |x| x.chomp }
# list is now %w[brillig gimble gyre slithy toves wabe]

要注意 必须调用close_write,如果没有调用它，读取管道的时候，就不能到达文件的末尾.

下面是一个block的形式：

File.popen("/usr/games/fortune") do |pipe|
  quote = pipe.gets
  puts quote
  # On a clean disk, you can seek forever. - Thomas Steel
end

File.popen("/usr/games/fortune") do |pipe|
  quote = pipe.gets
  puts quote
  # On a clean disk, you can seek forever. - Thomas Steel
end

如果指定了一个字符串"-"，那么一个新的ruby实例将被创建.如果指定了一个block，那么这个block将会作为两个独立

的进程运行。子进程得到nil，父进程得到一个IO对象：

IO.popen("-") do |mypipe|
  if mypipe
    puts "I'm the parent: pid = #{Process.pid}"
    listen = mypipe.gets
    puts listen
  else
    puts "I'm the child: pid = #{Process.pid}"
  end
end

# Prints:
#   I'm the parent: pid = 10580
#   I'm the child: pid = 10582

IO.popen("-") do |mypipe|
  if mypipe
    puts "I'm the parent: pid = #{Process.pid}"
    listen = mypipe.gets
    puts listen
  else
    puts "I'm the child: pid = #{Process.pid}"
  end
end

# Prints:
#   I'm the parent: pid = 10580
#   I'm the child: pid = 10582

pipe方法也返回互相连接的一对管道:

pipe = IO.pipe
reader = pipe[0]
writer = pipe[1]

str = nil
thread1 = Thread.new(reader,writer) do |reader,writer|
  # writer.close_write
  str = reader.gets
  reader.close
end

thread2 = Thread.new(reader,writer) do |reader,writer|
  # reader.close_read
  writer.puts("What hath God wrought?")
  writer.close
end

thread1.join
thread2.join

puts str         # What hath God wrought?

pipe = IO.pipe
reader = pipe[0]
writer = pipe[1]

str = nil
thread1 = Thread.new(reader,writer) do |reader,writer|
  # writer.close_write
  str = reader.gets
  reader.close
end

thread2 = Thread.new(reader,writer) do |reader,writer|
  # reader.close_read
  writer.puts("What hath God wrought?")
  writer.close
end

thread1.join
thread2.join

puts str         # What hath God wrought?

4 使用非阻塞IO

ruby会在后台执行一些操作，使io不会被阻断，因此大部分情况下可以使用ruby线程来管理IO,当一个线程被Io阻塞之

后，另外的线程能够继续执行.

由于ruby的线程不是一个native的线程，因此ruby的线程都在同一个进程里面.

如果你想关闭一个非阻塞io，你可以这样做:

require 'io/nonblock'

# ...

test = mysock.nonblock?         # false

mysock.nonblock = true          # turn off blocking
# ...
mysock.nonblock = false         # turn on again

mysock.nonblock { some_operation(mysock) }
# Perform some_operation with nonblocking set to true

mysock.nonblock(false) { other_operation(mysock) }
# Perform other_operation with non-blocking set to false

require 'io/nonblock'

# ...

test = mysock.nonblock?         # false

mysock.nonblock = true          # turn off blocking
# ...
mysock.nonblock = false         # turn on again

mysock.nonblock { some_operation(mysock) }
# Perform some_operation with nonblocking set to true

mysock.nonblock(false) { other_operation(mysock) }
# Perform other_operation with non-blocking set to false

5 使用readpartial

readpartial被设计来用于就像socket这样的流.

readpartial要求提供最大长度的参数，如果指定了buffer，那么这个buffer应指向用于存储数据的一个字符串。

data = sock.readpartial(128)  # Read at most 128 bytes

data = sock.readpartial(128)  # Read at most 128 bytes

readpartial 方法，不能接受非阻塞的flag,他有时会阻塞:IO对象的buffer是空的；流的内容为空；流没有到达文件末尾

。

因此，如果流中还有数据的话，readpartial将不会阻塞.

如果流没有数据，并且他已经抵达文件的末尾，readpartial 将会立即抛出一个EOFError.

如果调用阻塞，他将会等待直到接收到数据或者得到一个EOF.

当sysread 调用在阻塞模式下，他的行为与readpartial相似.

6 操作路径名


先来看一下File.dirname和File.basename方法：

str = "/home/dave/podbay.rb"
dir = File.dirname(str)           # "/home/dave"
file1 = File.basename(str)        # "podbay.rb"
file2 = File.basename(str,".rb")  # "podbay"

str = "/home/dave/podbay.rb"
dir = File.dirname(str)           # "/home/dave"
file1 = File.basename(str)        # "podbay.rb"
file2 = File.basename(str,".rb")  # "podbay"

File.split方法，可以将一个文件的路径名和文件名分隔开：

info = File.split(str)        # ["/home/dave","podbay.rb"]

info = File.split(str)        # ["/home/dave","podbay.rb"]

类方法expand_path 将一个相对路径，转换为一个绝对路径名：

Dir.chdir("/home/poole/personal/docs")
abs = File.expand_path("../../misc")    # "/home/poole/misc"

Dir.chdir("/home/poole/personal/docs")
abs = File.expand_path("../../misc")    # "/home/poole/misc"

对于打开的文件，path 将会返回这个文件的路径名：

file = File.new("../../foobar")

name = file.path                 # "../../foobar"

file = File.new("../../foobar")

name = file.path                 # "../../foobar"

类方法类方法join正好和split相反:

path = File.join("usr","local","bin","someprog")

path = File.join("usr","local","bin","someprog")

7使用Pathname

pathname类实际上是,Dir, File, FileTest,和FileUtils的包装器，它包含他们的很多功能:

require 'pathname'
path = Pathname.new("home/hal")
file = Pathname.new("file.txt")
p2 = path + file
path.directory?         # true
path.file?              # false
p2.directory?           # false
p2.file?                # true

puts parts = p2.split     # [Pathname:/home/hal, Pathname:file.txt]
puts ext = p2.extname     # .txt

require 'pathname'
path = Pathname.new("home/hal")
file = Pathname.new("file.txt")
p2 = path + file
path.directory?         # true
path.file?              # false
p2.directory?           # false
p2.file?                # true

puts parts = p2.split     # [Pathname:/home/hal, Pathname:file.txt]
puts ext = p2.extname     # .txt

再看看其他的有用的方法:

p1 = Pathname.new("//")           # odd but legal
p1.root?                          # true
p2 = Pathname.new("/home/poole")
p3 = p2.parent                    # Pathname:/home
items = p2.children               # array of Pathnames (all files and
                                  # dirs immediately under poole)

p1 = Pathname.new("//")           # odd but legal
p1.root?                          # true
p2 = Pathname.new("/home/poole")
p3 = p2.parent                    # Pathname:/home
items = p2.children               # array of Pathnames (all files and
                                  # dirs immediately under poole)

relative和absolute判断路径是否是相对的:

p1 = Pathname.new("/home/dave")
p1.absolute?                      # true
p1.relative?                      # false

p1 = Pathname.new("/home/dave")
p1.absolute?                      # true
p1.relative?                      # false

8 Command-Level 文件操作

其实也就是copy, delete, rename,等等 些操作了:

File.delete("history")
File.unlink("toast")
File.rename("Ceylon","SriLanka")
File.link("/etc/hosts","/etc/hostfile")   # hard link
File.symlink("/etc/hosts","/tmp/hosts")   # symbolic link
File.truncate("myfile",1000)    # Now at most 1000 bytes

File.delete("history")
File.unlink("toast")
File.rename("Ceylon","SriLanka")
File.link("/etc/hosts","/etc/hostfile")   # hard link
File.symlink("/etc/hosts","/tmp/hosts")   # symbolic link
File.truncate("myfile",1000)    # Now at most 1000 bytes

fileUtils也有很多有用的方法

require "fileutils"
same = FileUtils.compare_file("alpha","beta")  # true
# Copy epsilon to theta and log any errors.
FileUtils.copy("epsilon","theta", true)
FileUtils.move("/tmp/names","/etc")     # Move to new directory
FileUtils.move("colours","colors")      # Just a rename
FileUtils.safe_unlink("alpha","beta","gamma")
# Log errors on the next two files
FileUtils.safe_unlink("delta","epsilon",true)
FileUtils.install("foo.so","/usr/lib")

require "fileutils"
same = FileUtils.compare_file("alpha","beta")  # true
# Copy epsilon to theta and log any errors.
FileUtils.copy("epsilon","theta", true)
FileUtils.move("/tmp/names","/etc")     # Move to new directory
FileUtils.move("colours","colors")      # Just a rename
FileUtils.safe_unlink("alpha","beta","gamma")
# Log errors on the next two files
FileUtils.safe_unlink("delta","epsilon",true)
FileUtils.install("foo.so","/usr/lib")

9 从键盘抓取输入

也就是抓取用户从键盘输入的字符。
unix平台:

def getchar
  system("stty raw -echo")  # Raw mode, no echo
  char = STDIN.getc
  system("stty -raw echo")  # Reset terminal mode
  char
end

def getchar
  system("stty raw -echo")  # Raw mode, no echo
  char = STDIN.getc
  system("stty -raw echo")  # Reset terminal mode
  char
end

windows平台:

require 'Win32API'

def getchar
  char = Win32API.new("crtdll", "_getch", [], 'L').Call
end

require 'Win32API'

def getchar
  char = Win32API.new("crtdll", "_getch", [], 'L').Call
end

10 读取整个文件到内存

读取整个文件到数组，你不需要打开文件，IO.readlines 可以完成这个工作，他自己会open和close.

arr = IO.readlines("myfile")
lines = arr.size
puts "myfile has #{lines} lines in it."

longest = arr.collect {|x| x.length}.max
puts "The longest line in it has #{longest} characters."

arr = IO.readlines("myfile")
lines = arr.size
puts "myfile has #{lines} lines in it."

longest = arr.collect {|x| x.length}.max
puts "The longest line in it has #{longest} characters."

也可以用IO.read(它返回一个大的字符串):

str = IO.read("myfile")
bytes = arr.size
puts "myfile has #{bytes} bytes in it."

longest = str.collect {|x| x.length}.max     # strings are enumerable!
puts "The longest line in it has #{longest} characters."

str = IO.read("myfile")
bytes = arr.size
puts "myfile has #{bytes} bytes in it."

longest = str.collect {|x| x.length}.max     # strings are enumerable!
puts "The longest line in it has #{longest} characters."

由于File继承了IO,因此File也有这两个方法.

11 逐行迭代一个文件

我们可以使用IO.foreach 方法，或者each方法，如果是前者文件不需要显示打开:

# Print all lines containing the word "target"
IO.foreach("somefile") do |line|
  puts line if line =~ /target/
end

# Another way...
file = File.new("somefile")
file.each do |line|
  puts line if line =~ /target/
end

# Print all lines containing the word "target"
IO.foreach("somefile") do |line|
  puts line if line =~ /target/
end

# Another way...
file = File.new("somefile")
file.each do |line|
  puts line if line =~ /target/
end

12逐字节对文件进行遍历

可以使用each_byte方法，如果你想要转换byte到字符的话使用chr方法:

file = File.new("myfile")
e_count = 0
file.each_byte do |byte|
  e_count += 1 if byte == ?e
end

file = File.new("myfile")
e_count = 0
file.each_byte do |byte|
  e_count += 1 if byte == ?e
end

12 把字符串当文件来用

我们可以使用stringio库：

require 'stringio'

ios = StringIO.new("abcdefghijkl\nABC\n123")

ios.seek(5)
ios.puts("xyz")

puts ios.tell             # 8

puts ios.string.dump      # "abcdexyzijkl\nABC\n123"

c = ios.getc
puts "c = #{c}"           # c = 105

ios.ungetc(?w)

puts ios.string.dump      # "abcdexyzwjkl\nABC\n123"

puts "Ptr = #{ios.tell}"

s1 = ios.gets             # "wjkl"
s2 = ios.gets             # "ABC"

require 'stringio'

ios = StringIO.new("abcdefghijkl\nABC\n123")

ios.seek(5)
ios.puts("xyz")

puts ios.tell             # 8

puts ios.string.dump      # "abcdexyzijkl\nABC\n123"

c = ios.getc
puts "c = #{c}"           # c = 105

ios.ungetc(?w)

puts ios.string.dump      # "abcdexyzwjkl\nABC\n123"

puts "Ptr = #{ios.tell}"

s1 = ios.gets             # "wjkl"
s2 = ios.gets             # "ABC"

13读取嵌套在程序中的数据

ruby中程序末尾的__END__ 标记说明，下面的数据是程序内嵌的数据，你可以使用一个IO对象DATA来读取。

# Print each line backwards...
DATA.each_line do |line|
  puts line.reverse
end
__END__
A man, a plan, a canal... Panama!
Madam, I'm Adam.
,siht daer nac uoy fI
.drah oot gnikrow neeb ev'uoy

# Print each line backwards...
DATA.each_line do |line|
  puts line.reverse
end
__END__
A man, a plan, a canal... Panama!
Madam, I'm Adam.
,siht daer nac uoy fI
.drah oot gnikrow neeb ev'uoy

14 读取程序源码

DATA指向__END__ 后面的数据，如果你调用rewind,它将会将文件指针指向程序的开头:

DATA.rewind