insert into file without overwriting

[maackey]

So, my question isn't directly related to spring, but more of lua in general.

Is there a way I can easily insert eg. a string into a file without overwriting the contents?

I tried something like this:
file:write(abcdefghijklmn)
local bookmark = file:seek()
file:write(stuvwxyz)
file:seek("set", bookmark)
file:write(opqr)

but instead of getting output

Code: Select all

abcdefghijklmn
opqr
stuvwxyz

I get

Code: Select all

abcdefghijklmn
opqrwxyz

I've written spaces to "fill the gap" in the meantime, but since "opqr" is generated dynamically later on in the file it is very hard to predict how long it will be.

[Forboding Angel]

As food for thought, depending on what you are doing, it might be better to have a config file that gets included wherever the values are needed as a go between. That way you're not risking overwriting important stuff. And having one lua file write directly into another is O_o


That said, couldn't you just use a global variable?

[knorke]

Is there a way I can easily insert eg. a string into a file without overwriting the contents?

I dont think such thing is possible because of how files work?
imo read file into array, insert your stuff, write it again.
if you feel like being cautious you could write to a temp file and when everything worked, replace the orginal file with that.

or if you just want to add at the end of the file, "a" parameter is for append.

[zwzsg]

imo read file into array

Or read the whole file into a string. I have a widget that read files in the 50kb range into a string, apply some gsub to it, then write it to a file.

[maackey]

Thanks guys! I managed to get it working perfectly

As food for thought, depending on what you are doing, it might be better to have a config file that gets included wherever the values are needed as a go between. That way you're not risking overwriting important stuff. And having one lua file write directly into another is O_o


That said, couldn't you just use a global variable?

Its a lua file that generates verilog code. I can't use a variable, because I don't know how many wires there are and what they will be named.

or if you just want to add at the end of the file, "a" parameter is for append.

Can't append to the end of the file as the wires need to be defined before I use them ^^

r read the whole file into a string. I have a widget that read files in the 50kb range into a string, apply some gsub to it, then write it to a file.

Yeah apparently lua is a beast at strings.

Because Lua handles long strings efficiently, a simple technique for writing filters in Lua is to read the whole file into a string, do the processing to the string (typically with gsub), and then write the string to the output:

t = io.read("*all") -- read the whole file
t = string.gsub(t, ...) -- do the job
io.write(t) -- write the file

ended up using this, worked perfectly.

I attached the file if anyone is interested in seeing what it does/how horribly noobish I am at lua.