Bash and Pieces

Jan 10, 2018

Here is a list of “useful” bash commands that I always seem to forget …

Get CPU percentage

top -bn 2 -d 0.1 | grep -E '^(%)?Cpu' | tail -n 1 | awk '{print $2+$4+$6}'

# top -b        for batch
# top -n 2      for 2 sequences
# top -d 0.1    difference of 0.1 second
# grep -E       for regex pattern - some OS will start the line with %Cpu and some other won't
# tail -n 1     to get the last line
# awk           to add numbers up

Get Memory percentage

free -t | grep 'Total' | awk '{print ($3 * 100) / $2 }'

# free -t       to display the total
# grep          the last line
# awk           to make a percentage

Count the total number of docker containers

docker ps -aq | wc -l

# docker ps     will list the docker containers - you can filter stuff here with the --filter parameter
# wc -l         counts the total of line

Get a timestamp in seconds

date +%s%N | cut -b1-13

# cut -b1-13    will keep the 13 first digits which is what we want because the date will return the nano seconds

Prompt for user input with a timeout

Sometimes people fall asleep in front of their screen so a simple read -p "your question:" $value; will be prompted for ever… Add a timeout!

printf "What is your favourite colour?\n"
read -t 10 $colour;

if [[ $? = "1" ]]; then
    printf "Are you asleep?"
    read -t 10 $colour;
fi

Note that once the timeout of 10 seconds is reached, the command will fail with the error code “1”.

Running a PHP script forever with Supervisor

Let’s say you want to run a script forever (like a job queuing system that needs to constantly listen to incoming jobs) you could just start the process with a php my-script.php and be done with it (HAHA jk) but then how do you make sure it always run? And what if you want to monitor it?