How To | Read files using scripting

Learn how to use scripting to efficiently and effectively read files.

Updated at June 8th, 2023

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Procedure


There are two primary methods of reading (and writing) files via scripted methods: a Simple Method and a Complete I/O Model:

Tip

To learn how to write files using scripting, see the related article "How To | Write files using scripting"

 
--READING FILES
--Reading a File, Method 1
--The "Direct Way", Simple Model
io.input("design/MyTestFile")   --Open the file for reading     
thefile = io.read("*a")          --One way to do this
  --"a" means read the whole file.
  --The asterisk is optional in Lua 5.3 and beyond, but required in Lua 5.2 in before.
print ("This is Read Method #1, Entire File Read")
print (thefile)

--Or by line
print ("This is Read Method #1, Line-by-Line Read")
count = 0
for line in io.lines("design/MyTestFile") do
  count = count + 1
  print(count, line)
end
io.input("design/MyTestFile")   --Close file after use



--Reading a File, Method 2
  --The Complete I/O Model
  --use for advanced file manipulation, reading/writing to several files
myfile = io.open ("design/MyTestFile2","r")
  --r for Read-Only of existing file
  --w for Create/Write new file
  --a for Append Mode, this is for writing only
  --r+ for Read/Write existing file, will overwrite existing content
  --w+, same as "w", except reading is also allowed
  --a+, same as "a", except reading is also allowed
if myfile~=nil then
  thefile = myfile:read("*a")
    --"a" means read the whole file.
    --The asterisk is optional in Lua 5.3 and beyond, but required in Lua 5.2 in before.
  print("This is Read Method #2")
  print(thefile)
  io.close(myfile)              --Close file after use
else
  print("myfile==nil")
  --for certain argument usages a nil is returned if file does not exist
end

--The locations "design/" and "media/" are acceptable.
--The "media/" folder is generally for all media files, and the "design/" folder
--is where uncompressed design configuration files reside.
--Files in "design/" can be viewed at http://[ip_of_core]/designs/current_design