Do Things While a Bash Script is Running

Andrumen1 0
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I have a very simple bash script; call it test.sh for practical purposes:

#!/bin/bash

sleep 5s

echo "Program is done."

I have another script that must take statistics with the /usr/bin/time command, for which I have set the cf alias; call this script statistics.sh:

#!/bin/bash

# Make sure to add the aliases.
shopt -s expand_aliases
source ~/.bash_aliases

# Get the command name.
name=${1:2}
echo "Executing script: $1"
echo "Name of script: $name"

# Run the script and get the process id.
cf $1 &
procID=$!

# While the $1 script is running do.
while [ <The script with id $1 is running>  ]
do
   echo "Here"
   sleep 1s
done

wait

# Exit message.
echo "Done running the program."

I have failed to make the while loop (properly) work; i.e., print "Here" 5 (or 4?) times.

Running the Program

I run the program as:

./statistics.sh './test.sh'

Whenever I am running it without the while loop it works perfectly, without printing the desired strings...of course.

What I Have Tried

I am lost in the sea of literature and 'solutions', but I have tried to set the <The script with id $1 is running> as:

  • kill -0 $1 2> /dev/null (and variations of)
  • I have tried to use the trap command, but I don't think that I understand it properly and thus it's not working.
while-loop shell bash linux
2 Answers
while kill -0 "$procID" 2>/dev/null
do
    echo Here
    sleep 1
done

If the condition is a command, you don't put it inside []. [ is an alias for the test command, it's used for testing conditional expressions, not the status of other commands.

Barmar0
  1. launch the program into the background
  2. launch the "here" loop into the background as well
  3. wait for the program to complete
  4. then kill the here loop
cf "$1" &
procID=$!

( while true; do echo "Here"; sleep 1s; done ) &
loopID=$!

wait "$procID"
kill "$loopID"

We can give it some more pizzazz:

(
    spinner=('/' '-' '\' '|')
    # or: spinner=(' ' '░' '▒' '▓' '█' '▓' '▒' '░')
    # or: spinner=(' ' '○' '◎' '●' '◎' '○')
    n=${#spinner[@]}
    i=0
    while true; do
        printf '\r%s ' "${spinner[(i++)%n]}"
        sleep 0.1s
    done
) &
glenn jackman0
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