#unix #bash #cheatsheet

bash.md

Bash cheatsheet

• Bash cheatsheet
  • Helpful links
  • Tricks & tips
    • Wait until something works
    • tr
    • Check udp port
    • Check for argument
    • Cat content to file
    • Using journalctl & sytemctl
    • Compress folder while excluding certain files
    • Datadog troubleshoot
    • [Generate markdown table from @so0k link](#generate-markdown-table-from-so0k-linkhttpsgistgithubcomso0k256cde434cbb0b58702249b31203a357)
    • Ssh through jumphost
    • Set -e
    • Ssh issue
    • List all processes from pods list

Helpful links

• tmux cheatsheet link

• bash cheatsheet link

• Makefile cheatsheet link

• GPG cheatsheet link

• Exit code link

Tricks & tips

Wait until something works

until ping -c 1 mongo; do
  echo "waiting for DNS mongo..."
  sleep 2
done

tr

tr -s '[[:space:]]' '\n' : replace space with newline td -d '[:space:]' : remove all spaces

Check udp port

nc -zuv 192.168.0.10 123

Check for argument

  if [ -z "$1" ];then
    echo "Usage: ./create-users.sh <user-name>"
    exit 0
  fi

Cat content to file

cat > outfile.txt <<EOF
some text
to save
EOF

Using journalctl & sytemctl

# display last line
journalctl -b -1 -e

# follow log stream
journalctl -u <service> -f

# restart service
systemctl restart <service>

Compress folder while excluding certain files

tar -zcvf file.tar.gz --exclude=".git/*" --exclude="*.zip" .

Datadog troubleshoot

To display information about the Agent's state with this command.

debian:

docker exec dd-agent service datadog-agent info

alpine:

docker exec dd-agent /opt/datadog-agent/bin/agent info

Generate markdown table from @so0k link

import yaml

print_format="| {parameter:<40}| | {default:<50}|"
def walk_dict(d,keys=[],depth=0):
    for k,v in sorted(d.items(),key=lambda x: x[0]):
        keys.append(k)
        if isinstance(v,dict):
            walk_dict(v,keys,depth+1)
        else:
            print(print_format.format(parameter='`{0}`'.format(".".join(keys)),default='`{0}`'.format(v)))
        keys.pop()

s = open("./values.yaml")
d = yaml.load(s)

walk_dict(d)

Ssh through jumphost

ssh -o ProxyCommand='ssh <jump_host> nc %h %p' user@host

Set -e

set -e stops the execution of a script if a command or pipeline has an error - which is the opposite of the default shell behaviour, which is to ignore errors in scripts. Type help set in a terminal to see the documentation for this built-in command.

Ssh issue

ln -s ../Cellar/[email protected]/1.1.0f /usr/local/opt/[email protected]

List all processes from pods list

export NODE_NAME=<NODE_NAME> && export IFS=$'\n' && \
for i in $(kubectl get pod --all-namespaces -o wide | grep $NODE_NAME | awk '{print "kubectl exec -it -n "$1" "$2" -- sh -c \"hostname && ps aux\""}'); \
do bash -c "$i";done

k8s-bashrc

# Get resources
# kget <pod|deployment|svc> <resource-name> <option>
kget() {
  kubectl get $@
}

# Change context
# kctx <context-name>
kctx() {
  kubectl config use-context $1
}

# Change namespace
# kns <namespace-name>
kns() {
  kubectl config set-context $(kubectl config current-context) --namespace=$1
}

# Get current context
kcurrent() {
  kubectl config current-context
}

# Delete resources
# kdel <pod|deployment|svc> <resource-name> <option>
kdel() {
  kubectl delete $@
}

# Describe resources
# kdes <pod|deployment|svc> <resource-name> <option>
kdes() {
  kubectl describe $@
}