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I searched a bit on how to do this, but I cannot find a solution. I am using process substitution cause of necessity. I want to wait for all the processing to finish before proceeding.

How do I get the PID of my 'runner' FUNCTION below so I can wait for it?

Basically what it does is execute, then log the stdout, then log errors & errors to stdout. Works well except for the out of sequence responses.

"${@}" 1> >(2log) 2> >(2log2scr | tee >&2) pid=???? # <<< HERE while [ -e /proc/"$pid" ]; do sleep 0.1; done # <<< HERE

I tried things like the following but does not work:

  1. pid=$(exec sh -c "${@}" 1> >(2log) 2> >(2log2scr | tee >&2) )

  2. this works partially - it breaks my EVAL:

> runner success & > while [ -e /proc/$! ]; do sleep 0.1; done

OUTPUTS

started running FAILURE: **** 4.4.19(1)-release **** finished running EVAL IS:

Your help is appreciated.

The full script follows if you need it for testing:

#!/bin/bash logfile='test.log' logprep() { local in=$(cat) in=$(echo "$in" | perl -pe 's/\**//smig') # for proc subst # Return prepped string echo -e "preped for logging: '$in'" } 2log() { local in=$(cat) if [ "$in" != '' ]; then echo -e "$in" | logprep >>"$logfile" # out to logfile fi return 0 } 2log2scr() { local in=$(cat) # 2scr if [ "'$in'" != '' ]; then echo -e "$in"; fi # 2log if [ "$in" != '' ]; then echo -e "$in" > >(logprep >>"$logfile") # out to logfile fi return 0 } runner () { echo -e "started running\n" "${@}" 1> >(2log) 2> >(2log2scr | tee >&2) # <<< RUNNER #while [ -e /proc/15435 ]; do sleep 0.1; done # <<< HERE echo -e "finished running\n" } success() { eval 'version=$(echo "SUCCESS: **** ${BASH_VERSION} ****")' echo -e "$version"; return 0 } failure() { eval 'version=$(echo "FAILURE: **** ${BASH_VERSION} ****")' echo -e "$version" 1>&2; return 64 } runner success # to test a successful command runner failure # to test a command that errs echo "EVAL IS: $version"
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  • 1
    The script should already wait for it to finish before moving to the next line unless it is being sent to the background somehow. Commented Jun 13, 2019 at 17:17
  • its out of sequence Commented Jun 13, 2019 at 17:19
  • It's hard to successfully get stdout and stderr output properly interleaved as you would see it in your terminal: stdout is buffered but stderr is not, I think. Commented Jun 13, 2019 at 18:35

2 Answers 2

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The pid of a background process can be retrieved from the $! environment variable if it has been put into the background (via adding a & to the end of your command), i.e.

my-cmd & echo $!

Another option you could explore is using $$ (pid of current shell) within the executed shell, e.g.

exec sh -c 'echo $$ > t.pid && sleep 10' & echo $! # <-- pid of spawned shell pid=$(cat t.pid) # <-- pid of execed process in shell

Something like this will give you the pid in a temporary file named t.pid

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  • Hey jjj thanks for you nice comment. I tried your suggestion (my-cmd & echo $!) already but for some reason it breaks my EVAL. see my comment section on what I tried. Commented Jun 13, 2019 at 17:43
  • Glad you got it working - thanks for posting your final result Commented Jun 13, 2019 at 18:06
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The only way I got this working without breaking my EVAL was this:

runner () { echo -e "started running\n" "${@}" 1> >(2log) 2> >(2log2scr | tee >&2) while [ -e /proc/$! ]; do sleep 0.1; done echo -e "$pid finished running\n" }

The difference here is that I am just plainly accessing $! without any prior requirements. All suggestions everywhere mention that $! is accessed if we call our routine like so:

my-cmd & echo $!

It seems that this is not a requirement and that we can plainly access $! after any complex routine such as "${@}" 1> >(2log) 2> >(2log2scr | tee >&2) without using the '&' anywhere

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  • I wonder if $! is the pid of the stderr process substitution. That seems like it would be the last background process created. Commented Jun 13, 2019 at 18:42

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