Populate PS1 asynchronously

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                          I have a few git svn related functions that see if I have to pull/push from/to the repository.

My problem is that the functions I've written to gather this information are too slow. I'd like to make them async so that PS1 shows a default, if though the data produced by the functions is ready I want it printed.

I'd like to have these information in my prompt – so that, for example, I know if I have to pull – without doing a git svn fetch everytime.

This is the function I call to add a ↑ to my PS1 if I have to push my changes.

    function hasToPush {
        (($1 == 0)) && 
            (git svn dcommit --dry-run 2>/dev/null | grep -q "diff-tree" && echo "↑")
    }

These are the functions I call to add a ↓ if I have to pull. The first is used to refresh my index every 2 minutes so that I can do the (($latest > $current)) check.

    function loopingGitSvnFetch {
         sleep 120
         git svn fetch &>/dev/null
    }
    loopingGitSvnFetch &
    function hasToPull {
        (($1 == 0)) && (
            latest=$(git svn log | awk 'NR==2' | cut -d ' ' -f1 | tr -d 'r')
            current=$2
            (($latest > $current)) && echo "↓"
        )
    }

To make them async, I've tried to put them together like this:

    function async {
        {
         git diff-index --quiet --cached HEAD &>/dev/null
         dirty=$(echo $?)
         push=$(hasToPush $dirty)
         gitsvn=$(git svn info 2> /dev/null | grep Revision)
         gitsvn=${gitsvn#Revision: }
         pull=$(hastoPull $dirty $gitsvn)
         callback $push $pull
         } &
     }

But that produces the same slow behaviour.
I've tried to put results in a file and then read it after, but I don't like that approach.

I've thought about using PROMPT_COMMAND. But that would not be async; it would be on demand.

Could you shed some light on how PS1 behaves or on what I'm doing wrong?
Thank you in advance.


PS: Could someone with 300 rep add the async and ps1 tags?


EDIT: 

I added these line to my .bashrc as a simple test, it seemed to work, so having rewrote them (I reverted my previous attempt) seems was a good thing :)

    while true;
    do
        discoverScmInfo &>~/.ps1
        sleep 1
    done &
    PS1='$(customW)$(cat ~/.ps1)\$ '

I'll put this in a function and check if the job is already running before calling it.
Sorry about this, after all it seems that all I needed was to write about it. :)
                        
Asked by Alberto Zaccagni (385 rep)
Nov 23, 2011, 05:32 PM
Last activity: Apr 21, 2015, 06:22 PM
Populate PS1 asynchronously

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