There are two ways, with '+>' and '+<'. They are distinctly different and are used in different situations.

'+>' truncates the opened file, just like '>' does. That means the contents of the file before opening are lost. You can seek to a previous location and read/modify what you have written there. [ I've never needed to use this one, either. I'd suspect a design flaw if I did ]

'+<' is more like '<', open to read. The contents of the file are not clobbered, and the file position is set to the beginning. You can read the file and even modify it (if you preserve length or don't care about it). Having read to the end, you can freely append to it.

The commonest situation where you want to open r/w happens when the file must be flock'd to prevent races on its content. '+<' permits you to read and modify the file under a single lock.

For either, the seek, tell, and truncate builtins are often needed.

After Compline,
Zaxo

In reply to Re: Using +> for File Read/Write by Zaxo
in thread Using +> for File Read/Write by slloyd

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