Lua - Reading Files

Quiz

Lua provides I/O library to read and manipulate files. We can open a file in read mode using following ways−

Simple Model

content = io.read ([, mode])

Where−

mode− an optional mode specifying the access mode of the file.

This method reads the first line of the file if mode is not specified. Otherwise, as per mode, the content is returned.

Before reading a file, it should be opened using following syntax:

-- Opens a file specified by fileName in read mode
file = io.open(fileName, "r")

-- sets the default input file
io.input(file)

Complete Model

content = file.read ([, mode])

Where−

file− file handle returned by io.open().
mode− an optional mode specifying the access mode of the file.

This method reads the first line of the file if mode is not specified. Otherwise, as per mode, the content is returned.

Before reading a file, it should be opened using following syntax:

-- Opens a file specified by fileName in read mode
file = io.open(fileName, "r")

Read Modes

Let's explore the various options to read content of a file using read() method:

Sr.No.	Mode & Description
1	*"n"/"number"* Reads from the current file position and returns a number if exists at the file position or returns nil.
2	*"a"/"all"* Returns all the contents of file from the current file position.
3	*"l"/"lines"* Reads the line from the current file position, and moves file position to next line.
4	number Reads number of bytes specified in the function.

we will use a sample file example.txt as shown below−

example.txt

Welcome to tutorialspoint.com
Simply Easy Learning

Example - Read File line by Line

Let us now see how to read a file line by line.

main.lua

-- read a file content and returns the same
function readFile()
   -- Opens a file in read
   f = io.open("example.txt","r")
   -- read first line
   print(f:read())
   -- read next line   
   print(f:read())
   -- close the file handle
   f:close()
   -- return the contents
   return contents
end

-- read the file
readFile()

Output

When the above code is built and executed, it produces the following result −

Welcome to tutorialspoint.com
Simply Easy Learning

Example - Read File All at once

Let us now see how to read file contents in single call.

main.lua

-- read a file content and returns the same
function readFile()
   -- Opens a file in read
   f = io.open("example.txt","r")
   -- read all content
   print(f:read("*a"))
   -- close the file handle
   f:close()
   -- return the contents
   return contents
end

-- read the file
readFile()

Output

When the above code is built and executed, it produces the following result −

Welcome to tutorialspoint.com
Simply Easy Learning

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