Can I have a file with variable content?-CodePudding

Is it possible to have a file with variable content? (It's probably not possible but worth asking as other might know a solution.)

For example the content of file mydate.txt should always be what this bash (it can be any scripting language, used bash just for simplicity) snippet produce:

#!/bin/bash
date

So when I try to see the content of the mydate.txt file it should actually display current date.

For example

cat mydate.txt

should display

Fri Dec 23 09:54:05 AM EET 2022

CodePudding user response：

The given example and description looks (to me) like a (simple) wrapper function to execute the provided file ... if the file has execute permissions enabled:

mycat() { for fname in "$@"; do ./"${fname}"; done; }

Taking for a test drive:

$ mycat mydate.txt
Fri Dec 23 11:02:20 CST 2022

$ mycat mydate.txt mydate.txt mydate.txt
Fri Dec 23 11:21:07 CST 2022
Fri Dec 23 11:21:07 CST 2022
Fri Dec 23 11:21:07 CST 2022

NOTES:

if the file has not been marked as executable it gets (quite) a bit more complicated (eg, sourcing a file bypasses any shebang that may be needed for the contents of the script to 'run' correctly; do you have permission to (re)set the 'execute' bit?)
while this 'works' for the (relatively) simple example, I'm guessing it probably won't work in all of OP's scenarios in which case we'd need a more detailed problem description (and more examples)

CodePudding user response：

As suggested, the best answer is to use a FIFO (First In, First Out) file, maybe like this:

#!/bin/bash

[ -f "catme.txt" ] && rm catme.txt    # cleanup if needed
mkfifo catme.txt

trap 'rm catme.txt ; exit 1' SIGINT.  # try to clean up the nice way

while true
do
    date > catme.txt
    printf "data provided on %s\n" "`date`"
done

run the command and use control-c to exit it. Then in another terminal you would call cat catme.txt and you will see our current date. This may not be what you want, but you have to attach a process to something dynamic in unix, else you can try running the command from your other script.