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I have a shell script which gets triggerred and runs at regular interval again and again on linux system, say every 45 mins. I need to share certain information between different runs of this shell script. What are different ways I can implement this? This is somewhat similar to interprocess communication. I dont want to use disk I/O so no file creation. Something I can create in memory and can keep it alive for some time duration e.g. 7AM to 12AM etc. During this time, the scripts runs say 20 times and uses/populates that data structure again and again. The values populated in previous run need to be used in next run by the script.

Basically I am looking for something which works like DB but faster and modifying that is less expensive operation. So I will keep my data in that DB like thing and all differnt runs of script will read/modify that thing instead of going to DB again and again. /dev/shm looks good option unless someone suggests better option.

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    You could use tmpfs (like /dev/shm) but that's in virtual memory and may get swapped in 45 mins if there is other usage on that system. echo $BASHPID; $(echo $BASHPID >/dev/shm/foo); cat /dev/shm/foo; rm -f /dev/shm/foo Commented Jun 14, 2018 at 4:20
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    @melpomene I dont want to use I/O operation as this job is time critical. Commented Jun 15, 2018 at 0:29
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    If it's time critical, why are you using a shell script for this? Commented Jun 15, 2018 at 3:06
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    Internal functionality is written in java. Shell script is only triggering the main functionality repeatedly at regular interval. Commented Jun 17, 2018 at 3:15
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    Sounds like a job for Redis - an in-memory datastructure server with bindings for shell, PHP, Python, C, C++, Java... Commented Jun 17, 2018 at 8:51

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I dont want to use disk I/O so no file creation.

If you're on a Linux system, create a file in /dev/shm. Files stored in this directory are only stored in shared memory; they are not written to disk.

Depending on your system configuration, /tmp and/or /var/tmp may be mounted as a tmpfs, making them behave the same way. Your mileage may vary.

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Someone has commented above that this can get swapped in some time. Is that true? I want control over this file, creation/deletion etc.
@JamesBond If there's sufficient memory pressure on the system, yes. But that's unlikely to happen for a small file unless the system is completely out of memory.

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