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Reading a data file and sensing EOF in Lua

In Lua, the standard table io includes an io.open code element that lets you open a file. This returns a userdata to you (looks like a table but isn't - it's a C accessible structure) from which you can run the read code. Empty lines return an empty string (in Lua this is a TRUE value, unlike other languages), and at the end of file a nil is returned. See source code

You do need to write your reading loop as while true do, as you are not allowed to assign a value to a variable within the test condition - the = sign is not an operator in the same way that it is in other languages.

Covered on our Learning to Program in Lua course.
(written 2009-08-10)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
U110 - Lua - Input / Output
  [3558] Python or Lua - which should I use / learn? - (2011-12-21)
  [1841] Formatting with a leading + / Lua and Perl - (2008-10-15)
  [1744] Lua examples, Lua Courses - (2008-08-08)


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Automatically initialising Lua variables the first time
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