Bash scripting

I am writing a Linux bash scripts that I can run on a server or my own machine. Its purpose is to provide terminal output that immediately tells me about what is installed and running on that machine regarding the following:

Nginx (how is it configured)
Docker (which networks and containers are running and what is their setup)
Filesystem (what is to be found in the home directory)
PostgreSQL (is it root installed and if so, what databases, what tables, what ownership/permissions)

As bash script language is rather obscure, I publish here some advice I got from ChatGPT, some pitfalls I might encounter next time, and some work-in-progress scripts that contain working code.

ChatGPT advice

Here is a small block with general advice. Working with variables is painfull as the script language does not always make a difference between newline and space, following the guidelines below saves a lot of trouble. Furthermore the syntax of if-statements requires precision. Use [[ double square brackets and leave spaces between things.

#!/bin/bash
set -euo pipefail   # safer defaults
IFS=$'\n\t'         # strict input field splitting

# Always quote variables
echo "Hello, ${USER}"

# Use [[ ]] for tests, (with spaces around them)
if [[ "$name" == "Geert-Jan" ]]; then
    echo "Welcome back!"
fi

# Use functions
log() { echo "[LOG] $*"; }

# Use shellcheck
# -> a lint tool that points out errors and unsafe syntax

Few more advices:

No spaces when assigning variables. MYVAR="Hello" instead of `MYVAR = “HELLO”.
Tests can be multiple using && and/or ||
If you use [[ ]] for tests you can use == and !=.
jq is a library that helps to work with json output. Use it in pipes. My code shows examples and there is documentation.
shellcheck is not that good
Start nano editor with the -m flag, it lets you use your mouse to put the cursor anywhere.
To copy paste in nano, do cut-paste-paste (first paste to put the line back, second for the copy).
Docker commands provide output options with the –format flag. See Docker reference.
If you want styling of text using Unicod characters, use the -e flag in the echo command.
Variables can be used in commands, like "${MyVariable}"
Capitals are not required for variable names.

To assign a multiline string to a variable, for example if you want to create a long query string, this is a safe way:

QUERY=$(cat <<'EOF'
Just some string
that contains multiple 
lines
EOF
)

Sample code

The code below creates text output concerning Docker containers and networks.

set -euo pipefail
IFS=$'\n\t'

BLUEYELLOW='\e[44;93m'
RESETCOLOR='\e[0m'

echo ""
echo -e "${BLUEYELLOW}                                                                DOCKER                                                                                             ${RESETCOLOR}"
echo ""

docker ps --all
echo ""

QUERY2=$(cat <<'EOF'
SELECT * FROM buurten LIMIT 5;
EOF
)

do_query () {
  docker exec -it mijnwoonplaatsdbcontainer psql -U user01 -d db01 -At -c "$1"
}

#do_query "${QUERY2}"  // I disabled this one but you can do psql db query like this

docker network ls
echo""

for netwrk in $(docker network ls --format ''); do
  if [[ "$netwrk" != "host" && "$netwrk" != "bridge" && "$netwrk" != "none" ]]; then
    echo -e "Network \e[4;37m$netwrk\e[0m includes the following containers:"
    for name in $(docker network inspect "$netwrk" | jq -r '.[0].Containers | to_entries[] | .value.Name'); do
      echo -e "  \u2022 $name"
    done
  fi
done

echo ""
echo "CONTAINER DETAILS"

for container in $(docker ps --format ''); do
  echo -e "\u25AA \e[4;37m$container:\e[0m"
  #echo "$container:"
  NETWORKNAME=$(docker inspect "$container" | jq -r '.[0].HostConfig.NetworkMode')
  RESTARTPOLICY=$(docker inspect "$container" | jq -r '.[0].HostConfig.RestartPolicy.Name')
  echo "  Network: ${NETWORKNAME}"
  echo "  RestartPolicy: ${RESTARTPOLICY}"

  MOUNT_TYPE=$(docker inspect "$container" | jq -r '.[0].Mounts.[0].Type')
  MOUNT_NAME=$(docker inspect "$container" | jq -r '.[0].Mounts.[0].Name')
  MOUNT_SOURCE=$(docker inspect "$container" | jq -r '.[0].Mounts.[0].Source')
  MOUNT_DESTINATION=$(docker inspect "$container" | jq -r '.[0].Mounts.[0].Destination')
  echo "  Mounts (only first):"
  echo "    Type: ${MOUNT_TYPE}"
  echo "    Name: ${MOUNT_NAME}"
  echo "    Source: ${MOUNT_SOURCE}"
  echo "    Destination: ${MOUNT_DESTINATION}"
  echo ""
done

Docker

PostgreSQL Information Schema