Shell Scripts

Google Shell Style Guide: https://google.github.io/styleguide/shellguide.html

Bash Reference Manual: https://www.gnu.org/software/bash/manual/html_node/index.html

Pure bash snippets: https://github.com/dylanaraps/pure-bash-bible

Reusable Bash functions: https://github.com/gruntwork-io/bash-commons

Bash Guide: https://mywiki.wooledge.org/BashGuide - New version: https://guide.bash.academy - https://github.com/lhunath/guide.bash.academy

If statement

https://stackoverflow.com/questions/669452/are-double-square-brackets-preferable-over-single-square-brackets-in-b

https://stackoverflow.com/questions/3427872/whats-the-difference-between-and-in-bash

Ternary operator

[[ $b = 5 ]] && a="$c" || a="$d"
a=$([ "$b" == 5 ] && echo "$c" || echo "$d")

Check if directory exists

if [ -d src/app ]; then
  echo "Directory exists"
else
  mkdir src/app
fi

https://stackoverflow.com/questions/59838/how-do-i-check-if-a-directory-exists-or-not-in-a-bash-shell-script

Check if environment variable is set

if [[ -z $ENVIRONMENT ]]; then
  echo "ENVIRONMENT is empty"
else
  echo "ENVIRONMENT is set to '$ENVIRONMENT'"
fi

https://stackoverflow.com/questions/39296472/how-to-check-if-an-environment-variable-exists-and-get-its-value

Wait for some condition

https://linuxsimply.com/bash-scripting-tutorial/loop/until-loop/

Wait until a file exists(source):

until [ -f /tmp/examplefile.txt ]
do
  sleep 5
done
echo "File found"
exit

Wait for EFS mount target in EC2 (source):

while ! (echo > /dev/tcp/${FileSystem}.efs.${AWS::Region}.amazonaws.com/2049) >/dev/null 2>&1
do
  sleep 5
done

Arguments

• $@ stores all the arguments in a list of string
• $* stores all the arguments as a single string
• $# stores the number of arguments

https://stackoverflow.com/questions/9994295/what-does-mean-in-a-shell-script

https://stackoverflow.com/questions/3898665/what-is-in-bash

https://stackoverflow.com/questions/2761723/what-is-the-difference-between-and-in-shell-scripts

https://stackoverflow.com/questions/3008695/what-is-the-difference-between-and-in-bash

Input

echo "Enter your name"
read name

read -p "Enter your name" name

https://stackoverflow.com/questions/18544359/how-do-i-read-user-input-into-a-variable-in-bash

Parameter expansion

https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html

https://stackoverflow.com/questions/2642585/read-a-variable-in-bash-with-a-default-value

read -p "Enter your name" name
name=${name:-Peter}