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.close()

Closes the open file, if any.

Syntax

file.close()

Parameters

none

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.exists()

Determines whether the specified file exists.

Syntax

file.exists(filename)

Parameters

• filename file to check

Returns

true of the file exists (even if 0 bytes in size), and false if it does not exist

Example

files = file.list()
if files["device.config"] then
    print("Config file exists")
end

if file.exists("device.config") then
    print("Config file exists")
end

See also

file.list()

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

none

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()

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

none

Returns

nil

See also

file.remove()

file.fscfg ()

Returns the flash address and physical size of the file system area, in bytes.

Syntax

file.fscfg()

Parameters

none

Returns

• flash address (number)
• size (number)

Example

print(string.format("0x%x", file.fscfg()))

file.fsinfo()

Return size information for the file system, in bytes.

Syntax

file.fsinfo()

Parameters

none

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")

file.list()

Lists all files in the file system.

Syntax

file.list()

Parameters

none

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

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()

file.read()

Read content from the open file.

Syntax

file.read([n_or_str])

Parameters

• n_or_str:
  • if nothing passed in, read up to LUAL_BUFFERSIZE bytes (default 1024) or the entire file (whichever is smaller)
  • if passed a number n, then read the file until the lesser of n bytes, LUAL_BUFFERSIZE bytes, or EOF is reached. Specifying a number larger than the buffer size will read the buffer size.
  • if passed a string str, then read until str appears next in the file, LUAL_BUFFERSIZE bytes have been read, or EOF is reached

Returns

File content as a 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 bytes of 'init.lua'
file.open("init.lua", "r")
print(file.read(5))
file.close()

See also

• file.open()
• file.readline()

file.readline()

Read the next line from the open file. Lines are defined as zero or more bytes ending with a EOL ('\n') byte. If the next line is longer than LUAL_BUFFERSIZE, this function only returns the first LUAL_BUFFERSIZE bytes (this is 1024 bytes by default).

Syntax

file.readline()

Parameters

none

Returns

File content in string, line by line, including 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()

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()

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")

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()

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()

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()