In this case, how do I quickly increase the number stored in "foo"? the file has 10000 as content, and I have a new value to add to it quickly. Is there an atomic way to read,add, write a value to "foo"?
On Mon, Jan 4, 2021 at 8:15 AM Greg Wooledge <wool...@eeg.ccf.org> wrote: > On Fri, Jan 01, 2021 at 10:02:26PM +0100, Ángel wrote: > > Yes. In fact, you can already do that using an interface exactly > > identical to file operations: > > > > # Store a string in shared memory with key 'foo' > > echo "Hello world" > foo > > > > # Read value of key foo > > var="$(<foo)" > > > > > > You only need to use that on a tmpfs filesystem, and it will be stored > > in memory. Or, if you wanted to persist your shared memory between > > reboots, or between machines, you could place them instead on a local > > or networked filesystem. > > It should be noted that $(<foo) still forks a process. If you want the > script to be faster, you'll need some other way to read the data from > the file -- perhaps using the read -r -d '' command, or the mapfile > command. > > Other forms of IPC that are viable in scripts include using a FIFO that's > held open by both parent and child, or launching the child as a coprocess. > >
