Bash - is it possible to write to memory rather than a file

basildon · 09-23-2008, 04:55 PM

... and then read the memory back as if it were a file i.e. line by line?

matthewg42 · 09-23-2008, 05:13 PM

You could use a ramdisk, or if you don't want to use fread and friends, why not use shared memory?

i92guboj · 09-23-2008, 09:04 PM

Quote:

Originally Posted by matthewg42

You could use a ramdisk, or if you don't want to use fread and friends, why not use shared memory?

Just write to /dev/shm, you can put files there and then read them or do whatever.

pixellany · 09-23-2008, 09:57 PM

If you simply save in a variable, does that accomplish the same thing?

What problem are you trying to solve---ie why do you need to do this?

i92guboj · 09-24-2008, 07:17 AM

Quote:

Originally Posted by pixellany

If you simply save in a variable, does that accomplish the same thing?

What problem are you trying to solve---ie why do you need to do this?

I don't think that variables are the best way to achieve that, since he mentioned needing multiple lines. Remember that the space for environment variables is far more finite than the available virtual memory, and the available virtual memory is the only limit for /dev/shm. By default, half of the memory is the limit, but it can be specified via a mount option for tmpfs.

basildon · 09-24-2008, 08:13 AM

That sounds excellent

Could you please give me a couple of lines of code that show how to implement this i.e. write a few lines and then read them ?

H_TeXMeX_H · 09-24-2008, 10:44 AM

Code:

bash-3.1$ echo oaneuthnsoathue > /dev/shm/new
bash-3.1$ cat /dev/shm/new
oaneuthnsoathue

i92guboj · 09-24-2008, 12:07 PM

Quote:

Originally Posted by basildon

That sounds excellent

Could you please give me a couple of lines of code that show how to implement this i.e. write a few lines and then read them ?

If you intend to so something that's going to run for a few users (or a lot of them) concurrently, it might be a good idea to write this way:

Code:

my_shm_file="/dev/shm/$USER-$0"

echo "whatever" >> "$my_shm_file"

That's the basic thing, it all depends on what do you exactly need to do. If you need a fifo instead of a regular file, you can create it as well. With a fifo, the contents will dissapear from the file as it's consumed by any program. A random link illustrating it:

http://www.linuxjournal.com/article/2156