Shell

Get script dir

SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )

Check if command available

With command

if ! command -v aws &> /dev/null; then
    echo "aws could not be found"
    exit
fi

with type

if ! type uuid >/dev/null 2>&1; then
  echo "uuid command not found!"
  exit
fi

Set default value to variable

variable=${1:-default_value}

Expression	x set and not null	x set to null	x is unset	x after expression
${x:-default_value}	$x	default_value	default_value	$x
${x-default_value}	$x	$x (null string)	default_value	$x
${x:=default_value}	$x	default_value	default_value	default_value
${x=default_value}	$x	$x (null string)	default_value	default_value

set -Eeuo pipefail

Sources: vaneyckt.io / gnu.org

• e/errexit: cause a bash script to exit immediately when a command fails
• E: any trap on ERR is inherited by shell functions, command substitutions, and commands executed in a subshell environment. The ERR trap is normally not inherited in such cases. (means that trap is triggered even if -e is set)
• u/nounset: treat unset variables as an error and exit immediately
• pipefail: sets the exit code of a pipeline to that of the rightmost command to exit with a non-zero status
• e/xtrace: Print a trace

set -x for debugging

if [[ -n "${TRACE-}" ]]; then set -o xtrace; fi

Traps

Sources: tldp.org

# trap EXIT and kill awslogs process
trap "killall awslogs" EXIT

Testing TLS/SSL/HTTPS certs

https://github.com/drwetter/testssl.sh

./testssl.sh https://my-url.foobar.baz