Re: Prepending text to the beginning of a file

[Greg Wooledge]

On Fri, Jun 17, 2022 at 09:01:50AM -0400, Chet Ramey wrote:
> On 6/16/22 4:48 PM, Akbarkhon Variskhanov wrote:
> 
> > To be honest, I can't quite grasp the <> operator's purpose.
> 
> It opens the named file for reading and writing, no more, no less.

I've never seen a script that uses the <> opening mode on a regular file.
The types of files that shell scripts deal with are simply not compatible
with that kind of operation, and the shell doesn't have a builtin "lseek"
command for random access to a file opened in this mode, either.

The only place I've ever seen <> used in a script is when opening a TCP
socket.  For example,

exec 3<>/dev/tcp/www.google.com/80
printf 'HEAD / HTTP/1.1\r\nHost: www.google.com\r\nConnection: close\r\n\r\n' 
>&3
cat <&3
exec 3>&-