nodemcu-firmware/docs/en/modules/file.md

file Module

The file module provides access to the file system and its individual files.

The file system is a flat file system, with no notion of directories/folders.

Only one file can be open at any given time.

file.fsinfo()

Return size information for the file system, in bytes.

####Syntax file.fsinfo()

####Parameters nil

####Returns

• remaining (number)
• used (number)
• total (number)

####Example

  -- get file system info
  remaining, used, total=file.fsinfo()
  print("\nFile system info:\nTotal : "..total.." Bytes\nUsed : "..used.." Bytes\nRemain: "..remaining.." Bytes\n")
            ```

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file.format()

Format the file system. Completely erases any existing file system and writes a new one. Depending on the size of the flash chip in the ESP, this may take several seconds.

####Syntax file.format()

####Parameters nil

####Returns nil

####Example

    file.format()

####See also

• file.remove()

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file.list()

Lists all files in the file system.

####Syntax file.list()

####Parameters nil

####Returns a lua table which contains the {file name: file size} pairs

####Example

    l = file.list();
    for k,v in pairs(l) do
      print("name:"..k..", size:"..v)
    end

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file.remove()

Remove a file from the file system. The file must not be currently open.

###Syntax file.remove(filename)

####Parameters

• filename: file to remove

####Returns nil

####Example

    -- remove "foo.lua" from file system.
    file.remove("foo.lua")

####See also

• file.open()

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file.rename()

Renames a file. If a file is currently open, it will be closed first.

####Syntax file.rename(oldname, newname)

####Parameters

• oldname: old file name
• newname: new file name

####Returns true on success, false on error.

####Example

    -- rename file 'temp.lua' to 'init.lua'.
    file.rename("temp.lua","init.lua")

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file.open()

Opens a file for access, potentially creating it (for write modes).

When done with the file, it must be closed using file.close().

####Syntax file.open(filename, mode)

####Parameters

• filename: file to be opened, directories are not supported
• mode:
  • "r": read mode (the default)
    
  • "w": write mode
    
  • "a": append mode
    
  • "r+": update mode, all previous data is preserved
    
  • "w+": update mode, all previous data is erased
    
  • "a+": append update mode, previous data is preserved, writing is only allowed at the end of file

####Returns

• nil if file not opened, or not exists (read modes). true` if file opened ok.

####Example

    -- open 'init.lua', print the first line.
    file.open("init.lua", "r")
    print(file.readline())
    file.close()

####See also

• file.close()
• file.readline()

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file.close()

Closes the open file, if any.

####Syntax file.close()

####Parameters nil

####Returns nil

####Example

    -- open 'init.lua', print the first line.
    file.open("init.lua", "r")
    print(file.readline())
    file.close()

####See also

• file.open()

---

file.readline()

Read the next line from the open file.

####Syntax file.readline()

####Parameters nil

####Returns File content in string, line by line, include EOL('\n'). Return nil when EOF.

####Example

    -- print the first line of 'init.lua'
    file.open("init.lua", "r")
    print(file.readline())
    file.close()

####See also

• file.open()
• file.close()
• file.read()

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file.writeline()

Write a string to the open file and append '\n' at the end.

####Syntax file.writeline(string)

####Parameters

• string: content to be write to file

####Returns true if write ok, nil on error.

####Example

    -- open 'init.lua' in 'a+' mode
    file.open("init.lua", "a+")
    -- write 'foo bar' to the end of the file
    file.writeline('foo bar')
    file.close()

####See also

• file.open()
• file.readline()

---

file.read()

Read content from the open file. ####Syntax file.read([n_or_str])

####Parameters

• n_or_str:
  • if nothing passed in, read all byte in file.
  • if pass a number n, then read n bytes from file, or EOF is reached.
  • if pass a string "str", then read until 'str' or EOF is reached.

####Returns File content in string, or nil when EOF.

####Example

    -- print the first line of 'init.lua'
    file.open("init.lua", "r")
    print(file.read('\n'))
    file.close()

    -- print the first 5 byte of 'init.lua'
    file.open("init.lua", "r")
    print(file.read(5))
    file.close()

####See also

• file.open()
• file.readline()

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file.write()

Write a string to the open file.

####Syntax file.write(string)

####Parameters string: content to be write to file.

####Returns true if the write is ok, nil on error.

####Example

    -- open 'init.lua' in 'a+' mode
    file.open("init.lua", "a+")
    -- write 'foo bar' to the end of the file
    file.write('foo bar')
    file.close()

####See also

• file.open()
• file.writeline()

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file.flush()

Flushes any pending writes to the file system, ensuring no data is lost on a restart. Closing the open file using file.close() performs an implicit flush as well.

####Syntax file.flush()

####Parameters nil

####Returns nil

####Example

    -- open 'init.lua' in 'a+' mode
    file.open("init.lua", "a+")
    -- write 'foo bar' to the end of the file
    file.write('foo bar')
    file.flush()
    -- write 'baz' too
    file.write('baz')
    file.close()

####See also

• file.close()

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file.seek()

Sets and gets the file position, measured from the beginning of the file, to the position given by offset plus a base specified by the string whence.

####Syntax file.seek([whence [, offset]])

####Parameters

• whence:
  • "set": base is position 0 (beginning of the file)
  • "cur": base is current position (default value)
  • "end": base is end of file
• offset: default 0

If no parameters are given, the function simply returns the current file offset.

####Returns The resulting file position, or nil on error.

####Example

    file.open("init.lua", "r")
    -- skip the first 5 bytes of the file
    file.seek("set", 5)
    print(file.readline())
    file.close()

####See also

• file.open()

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