[SOLVED] Trying to exit main command from a piped grep condition

Issue

I'm struggling to find a good solution for what I'm trying to do.

So I have a CreateReactApp instance that is booted through a yarn run start:e2e. As soon as the output from that command has "Compiled successfully", I want to be able to run next command in the bash script.

Different things I tried:

if yarn run start:e2e | grep "Compiled successfully"; then
  exit 0
fi
echo "THIS NEEDS TO RUN"

This does appear to stop the logs, but it does not run the next command.

yarn run start:e2e | while read -r line;
do
  echo "$line"
  if [[ "$line" == *"Compiled successfully!"* ]]; then
    exit 0
  fi
done
echo "THIS NEEDS TO RUN"

yarn run start:e2e | grep -q "Compiled successfully";
echo $?
echo "THIS NEEDS TO RUN"

I've read about the differences between pipes / process substitions, but don't see a practical implementation regarding my use case..

Can someone enlighten me on what I'm doing wrong?

Thanks in advance!

---

EDIT: Because I got multiple proposed solutions and none of those worked I'll maybe redefine my main problem a bit.

1. So the yarn run start:e2e boots op a react app, that has a sort of "watch" mode. So it keeps spewing out logs after the "Compiled successfully" part, when changes occur to the source code, typechecks, ....
   After the React part is booted (so if the log Compiled succesfully is outputted) the logs do not matter anymore but the localhost:3000 (that the yarn compiles to) must remain active.

2. Then I run other commands after the yarn run to do some testing on the localhost:3000

So basically what I want to achieve in pseudo (the pipe stuff in command A is very abstract and may not even look like the correct solution but trying to explain thoroughly):

# command A
yarn run dev | cmd_to_watch_the_output "Compiled succesfully" | exit 0 -> localhost:3000 active but the shell is back in 'this' window

-> keep watching the output until Compiled succesfully occurs
-> If it occurs, then the logs does not matter anymore and I want to run command B

# command B
echo "I WANT TO SEE THIS LOG"
... do other stuff ...

I hope this clears it up a bit more :D 

Thanks already for the propositions!

Solution

If you want yarn run to keep running even after Compiled successfully, you can't just pipe its stdout to another program that exits after that line: that stdout needs to have somewhere to go so yarn's future attempts to write logs don't fail or block.

#!/usr/bin/env bash
case $BASH_VERSION in
  ''|[0-3].*|4.[012].*) echo "Error: bash 4.3+ required" >&2; exit 1;;
esac

exec {yarn_fd}< <(yarn run); yarn_pid=$!
while IFS= read -r line <&$yarn_fd; do
  printf '%s\n' "$line"
  if [[ $line = *"Compiled successfully!"* ]]; then
    break
  fi
done
# start a background process that reads future stdout from `yarn run`
cat <&$yarn_fd >/dev/null & cat_pid=$!
# close the FD from that background process so `cat` has the only copy
exec {yarn_fd}<&-

echo "Doing other things here!"
echo "When ready to shut down yarn, kill $yarn_pid and $cat_pid"

Answered By - Charles Duffy

Answer Checked By - Gilberto Lyons (WPSolving Admin)