Reading and writing files · Lessons

A file is a container

The simplest way to use a file in xTalk is to treat it as a container, like a variable or a field. URL "file:" followed by the file's path reads the whole file, and putting into it writes the whole file:

ExampleRun it in the playground

put specialFolderPath("temporary") & "/oxt-lesson-notes.txt" into tPath
put "First line" & return & "Second line" into URL ("file:" & tPath)
put URL ("file:" & tPath) into tText
put the number of lines of tText
put line 2 of tText
put there is a file tPath
delete file tPath
put there is a file tPath

Output

2
Second line
true
false

Use after to add to the end of a file without reading it first, which is handy for a log:

ExampleRun it in the playground

put specialFolderPath("temporary") & "/oxt-lesson-log.txt" into tPath
put "started" into URL ("file:" & tPath)
put return & "working" after URL ("file:" & tPath)
put return & "finished" after URL ("file:" & tPath)
put URL ("file:" & tPath)
delete file tPath

Output

started
working
finished

file: or binfile:

file: reads and writes text, and changes line endings to suit the system. binfile: reads and writes the bytes exactly as they are: use it for pictures, sound and any data that is not plain text, and for text whose encoding you choose yourself:

ExampleRun it in the playground

put specialFolderPath("temporary") & "/oxt-lesson-utf8.txt" into tPath
put textEncode("café ☕", "UTF-8") into URL ("binfile:" & tPath)
put the number of bytes of URL ("binfile:" & tPath)
put textDecode(URL ("binfile:" & tPath), "UTF-8")
delete file tPath

Output

9
café ☕

Where to keep files

A program should not scatter files anywhere. specialFolderPath gives the right folder on every system:

specialFolderPath("documents"): the user's documents, for files they made and will look for;
specialFolderPath("support"): the place for a program's own settings and data (add a folder with your program's name);
specialFolderPath("temporary"): for files you need only for a moment, as in these examples;
specialFolderPath("home") and specialFolderPath("desktop").

Paths in xTalk always use / between folders, on Windows too, so the same script works everywhere. With the itemDelimiter set to /, a path's items are its folders:

ExampleRun it in the playground

put "/home/ada/notes/todo.txt" into tPath
set the itemDelimiter to slash
put item -1 of tPath
put item 1 to -2 of tPath
set the itemDelimiter to "."
put item -1 of tPath

Output

todo.txt
/home/ada/notes
txt

Folders and listing files

files(folder) lists the files in a folder, a line each, and folders(folder) its folders. create folder, rename file and delete file and delete folder do what they say:

ExampleRun it in the playground

put specialFolderPath("temporary") & "/oxt-lesson-folder" into tFolder
create folder tFolder
put "a" into URL ("file:" & tFolder & "/b.txt")
put "b" into URL ("file:" & tFolder & "/a.txt")
put "c" into URL ("file:" & tFolder & "/c.csv")
put files(tFolder) into tFiles
sort tFiles
put tFiles
filter tFiles with "*.txt"
put the number of lines of tFiles
rename file (tFolder & "/c.csv") to (tFolder & "/d.csv")
put there is a file (tFolder & "/d.csv")
repeat for each line tFile in files(tFolder)
   delete file (tFolder & "/" & tFile)
end repeat
delete folder tFolder
put there is a folder tFolder

Output

a.txt
b.txt
c.csv
2
true
false

When a file cannot be read

Reading a file that is not there does not stop the script. The URL is empty and the result says what went wrong, so check it:

ExampleRun it in the playground

put URL "file:/no/such/folder/settings.txt" into tSettings
if the result is not empty then
   put "Could not read the settings:" && the result
end if

Output

Could not read the settings: can't open file

Try it yourself

Save a high-score table (one line per player, name,score) to a file in the temporary folder, read it back, add a new score, sort the table highest first, save it again, and put the top line. Delete the file at the end.

Show a solution

ExampleRun it in the playground

put specialFolderPath("temporary") & "/oxt-lesson-scores.txt" into tPath
put "Kim,340" & return & "Lee,875" into URL ("file:" & tPath)
put URL ("file:" & tPath) into tScores
put return & "Raj,1200" after tScores
sort lines of tScores numeric descending by item 2 of each
put tScores into URL ("file:" & tPath)
put line 1 of URL ("file:" & tPath)
delete file tPath

Output

Raj,1200

Words in this lesson

URLfile:binfile:specialFolderPathfilesfoldersthere is a filedelete filecreate folderrenamedefaultFolder

Each one finds every lesson that uses it. The Dictionary has the whole story of each, with its syntax and more examples.