Difference between revisions of "Fs.open"

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m (Fixed up some parts that weren't clear. fixed links to nil)
m (More use of Template:Type)
 
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{{Function
 
{{Function
 
|name=fs.open
 
|name=fs.open
−
|args=[[string (type)|string]] path, [[string (type)|string]] mode
+
|args={{Type|string}} path, {{Type|string}} mode
 
|api=fs
 
|api=fs
−
|returns=[[Table_(type)|Table]] the file handle, or [[Nil|nil]] if the mode was read-only and the file did not exist
+
|returns={{Type|table}} the file handle, or {{Type|nil}} on error (e.g. if <var>mode</var> was "r" and the file did not exist, or if <var>mode</var> was "w" or "a" and the file was in a read-only location)
 
|desc=
 
|desc=
 
'''Supported File Modes'''
 
'''Supported File Modes'''
−
Opens a file; <var>mode</var> consists of a first character which is one of the following
+
Opens a file so it can be read or written. <var>mode</var> consists of a first character which is one of the following:
−
"r" to open the file read-only,  
+
* "r" to open the file read-only,  
 +
* "w" to open it for writing and remove any existing data on file open, or
 +
* "a" to open for writing but keep existing data and append any writes to the end of the file
 +
Any of the three may be optionally followed by "b" to open the file for binary access instead of the default text access (eg, "wb" opens a file for binary output).
  
−
"w" to open it for writing and remove any existing data on file open, or
+
Text mode file handles assume UTF-8 encoding for both input and output purposes, and supports all characters within the [https://en.wikipedia.org/wiki/ISO/IEC_8859-1 ISO 8859-1 codepage] (plus a few extras). Prior to ComputerCraft 1.76, instead only [https://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters printable ASCII] characters are supported. In either case, any characters ''not'' supported are translated to 0x3F (representing a question mark).
  
−
"a" to open for writing but keep existing data and append any writes to the end of the file, plus optionally the second character
+
When you have opened a file you must always [[#Closing a file handle|close the file handle]], or else data may not be saved.
  
−
"b" to open the file for binary access instead of text access
+
Append mode and write mode both create a new file if none already exists (and write mode creates a new one even if one does); however, under a few builds of ComputerCraft in the 1.5x range, append mode will fail if an existing file cannot be found.
−
(text mode will perform end-of-line conversions necessary to move text files between Windows, Linux, and Mac OS systems; binary files should not have these conversions applied as they will be corrupted)
+
−
 
+
−
When you have opened a file you must always close the file handle, or else data will not be saved.
+
 
|examples=
 
|examples=
 
{{Example
 
{{Example
 
|desc=Creates the file "abcd" for writing, and holds a file handle to it
 
|desc=Creates the file "abcd" for writing, and holds a file handle to it
−
|code=h = fs.open("abcd", "w")
+
|code=local h = fs.open("abcd", "w")
 +
}}
 +
{{Example
 +
|desc=Opens "abcd" in either append or write mode, depending on whether it already exists or not.
 +
|code=local h = fs.open("abcd", fs.exists("abcd") and "a" or "w")
 
}}
 
}}
 
}}
 
}}
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=== Closing a file handle ===
 
=== Closing a file handle ===
  
−
When you open a file you must remember to then close the handle! With the write modes supported by ComputerCraft all the data that you are writing to a file will not be written into the file until you close the file. A file opened in any mode exposes the following close function.
+
When you open a file you must remember to close the handle when you've finished with it! The write modes supported by ComputerCraft may not actually output data until this is done. A file opened in any mode exposes the following close function:
 
{{Function
 
{{Function
 
|name=<var>h</var>.close
 
|name=<var>h</var>.close
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|name=<var>h</var>.readLine
 
|name=<var>h</var>.readLine
 
|api=fs
 
|api=fs
−
|returns=[[string]] the next line read from the file, with the end-of-line character stripped; or nil if there are no more lines in the file
+
|returns={{type|string}} the next line read from the file, with the end-of-line character stripped; or nil if there are no more lines in the file
 
|desc=Reads the next line from the file
 
|desc=Reads the next line from the file
 
}}
 
}}
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|name=<var>h</var>.readAll
 
|name=<var>h</var>.readAll
 
|api=fs
 
|api=fs
−
|returns=[[string]] the entire rest of the file, with the end-of-line character on the very last line (if present) stripped
+
|returns={{type|string}} the entire rest of the file, with the end-of-line character on the very last line (if present) stripped
 
|desc=Reads the all the text in the file
 
|desc=Reads the all the text in the file
 
}}
 
}}
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{{Function
 
{{Function
 
|name=<var>h</var>.write
 
|name=<var>h</var>.write
−
|args=[[string (type)|string]] data
+
|args={{type|string}} data
 
|api=fs
 
|api=fs
 
|desc=Writes a string of characters to the file exactly as they appear in the string <var>data</var>
 
|desc=Writes a string of characters to the file exactly as they appear in the string <var>data</var>
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{{Function
 
{{Function
 
|name=<var>h</var>.writeLine
 
|name=<var>h</var>.writeLine
−
|args=[[string (type)|string]] data
+
|args={{type|string}} data
 
|api=fs
 
|api=fs
 
|desc=Writes a string of characters to the file, then appends an end-of-line character
 
|desc=Writes a string of characters to the file, then appends an end-of-line character
 +
}}
 +
if you just want to save a file, without closing the handle, then you could do a flush. ( this is normally used for logging etc...)
 +
{{Function
 +
|name=<var>h</var>.flush
 +
|api=fs
 +
|desc=Flushes the data to the specified file. (keeps the handle available afterwards)
 
}}
 
}}
  
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|name=<var>h</var>.read
 
|name=<var>h</var>.read
 
|api=fs
 
|api=fs
−
|returns=[[int (type)|int]] the byte read from the file, or [[Nil|nil]] if there are no more bytes
+
|returns={{type|number}} the byte read from the file, or {{type|nil}} if there are no more bytes
 
|desc=Reads a single byte from the file and returns it
 
|desc=Reads a single byte from the file and returns it
 
}}
 
}}
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{{Function
 
{{Function
 
|name=<var>h</var>.write
 
|name=<var>h</var>.write
−
|args=[[int (type)|int]] byte
+
|args={{type|number}} byte
 
|api=fs
 
|api=fs
 
|desc=Writes a single byte into the file
 
|desc=Writes a single byte into the file

Latest revision as of 21:08, 9 June 2016


Grid Redstone.png  Function fs.open
Supported File Modes

Opens a file so it can be read or written. mode consists of a first character which is one of the following:

  • "r" to open the file read-only,
  • "w" to open it for writing and remove any existing data on file open, or
  • "a" to open for writing but keep existing data and append any writes to the end of the file

Any of the three may be optionally followed by "b" to open the file for binary access instead of the default text access (eg, "wb" opens a file for binary output).

Text mode file handles assume UTF-8 encoding for both input and output purposes, and supports all characters within the ISO 8859-1 codepage (plus a few extras). Prior to ComputerCraft 1.76, instead only printable ASCII characters are supported. In either case, any characters not supported are translated to 0x3F (representing a question mark).

When you have opened a file you must always close the file handle, or else data may not be saved.

Append mode and write mode both create a new file if none already exists (and write mode creates a new one even if one does); however, under a few builds of ComputerCraft in the 1.5x range, append mode will fail if an existing file cannot be found.
Syntax fs.open(string path, string mode)
Returns table the file handle, or nil on error (e.g. if mode was "r" and the file did not exist, or if mode was "w" or "a" and the file was in a read-only location)
Part of ComputerCraft
API fs

Examples

Grid paper.png  Example
Creates the file "abcd" for writing, and holds a file handle to it
Code 
local h = fs.open("abcd", "w")



Grid paper.png  Example
Opens "abcd" in either append or write mode, depending on whether it already exists or not.
Code 
local h = fs.open("abcd", fs.exists("abcd") and "a" or "w")


File Handles

A file handle allows access to a file. A file handle is a table; the functions within the table are accessed with the dot operator (not the colon operator, as may be more intuitive!). The examples below assume a file has already been opened and the handle stored in the variable h.

Closing a file handle

When you open a file you must remember to close the handle when you've finished with it! The write modes supported by ComputerCraft may not actually output data until this is done. A file opened in any mode exposes the following close function:

Grid Redstone.png  Function h.close
Closes the file handle, after which it can no longer be used
Syntax h.close()
Returns nil
Part of ComputerCraft
API fs


Files opened in text read mode

A file opened in mode "r" (text read mode) exposes the following functions.


Grid Redstone.png  Function h.readLine
Reads the next line from the file
Syntax h.readLine()
Returns string the next line read from the file, with the end-of-line character stripped; or nil if there are no more lines in the file
Part of ComputerCraft
API fs


Grid Redstone.png  Function h.readAll
Reads the all the text in the file
Syntax h.readAll()
Returns string the entire rest of the file, with the end-of-line character on the very last line (if present) stripped
Part of ComputerCraft
API fs


Files opened in text write/append mode

A file opened in mode "w" (text write mode) or "a" (text append mode) exposes the following functions:


Grid Redstone.png  Function h.write
Writes a string of characters to the file exactly as they appear in the string data
Syntax h.write(string data)
Returns nil
Part of ComputerCraft
API fs


Grid Redstone.png  Function h.writeLine
Writes a string of characters to the file, then appends an end-of-line character
Syntax h.writeLine(string data)
Returns nil
Part of ComputerCraft
API fs


if you just want to save a file, without closing the handle, then you could do a flush. ( this is normally used for logging etc...)

Grid Redstone.png  Function h.flush
Flushes the data to the specified file. (keeps the handle available afterwards)
Syntax h.flush()
Returns nil
Part of ComputerCraft
API fs


Files opened in binary read mode

A file opened in mode "rb" (binary read mode) exposes the following functions:


Grid Redstone.png  Function h.read
Reads a single byte from the file and returns it
Syntax h.read()
Returns number the byte read from the file, or nil if there are no more bytes
Part of ComputerCraft
API fs


Files opened in binary write/append mode

A file opened in mode "wb" (binary write mode) or "ab" (binary append mode) exposes the following functions:


Grid Redstone.png  Function h.write
Writes a single byte into the file
Syntax h.write(number byte)
Returns nil
Part of ComputerCraft
API fs
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