Best script practices

Bash is an ideal systems language for UNIX or command line tasks. Of course, in some cases it's better to use systems languages like C or Go. However, Bash can solve almost all of your problems, you just need to use it.

Basic Rules

It’s recommended to apply Clean Code principles while working with Bash.

All code blocks should be commented. Thus, it makes the script easier to read and understand.

Always double quote variables, including subshells. No naked $ signs.

echo "Names without double quotes"
echo
names="Codica Shell Practises"
for name in $names; do
   echo "$name"
done
echo

echo "Names with double quotes"
echo
for name in "$names"; do
   echo "$name"
done

Variables

Variables is used to store your values. You should operate them carefully, because sometimes Bash sometimes can use undeclared variables.
Concerning variables, use names that reflect the values stored in them, but try to make it more briefly.
Make static variables read-only.
```
# Password file variable
readonly passwd_file='/etc/passwd'
```
- Always use local when setting variables, unless there is reason to use declare.
  - An exception to this are cases when you are intentionally setting a variable in an outer scope.
```
func(){
    cd $PWD
}
```

Functions

Functions are created to reduce the amount of code. Try to write brief functions, that do only one task if it is possible.
Declare variables with a meaningful name for positional parameters of functions.
- Use UNIX-like approach: a function does one thing.
```
 # Function description
func(){
    printf("Hello world!")
}
```

I/O

Your script will sometimes require input from user. Try to make a clear message of your script requirements and don't forget to handle all correctly.
You should prefer printf to echo.
- printf gives more control over the output, it’s more portable and its behaviour is defined better.
- Your script should always react to abnormal input.
```
func(){
    echo -e "Unexpected argument!"
}
```
- It should always return 0 in case of a success and another value otherwise. It would be great if you can handle those.
- If your script requires user input, use prompts.
```
printf "Input email: "
read email
printf "$email"
```

Security

Security is very important thing. When writing a script be prepared for that your script will be executed by a less experienced person, so you should make your script fool-proof.
Don't store your credentials in shell scripts, people can have access to your script. Use ENV variables or vaults instead.
- You should always remember that your script can be executed on other machines or in container, so you need to use environment variables i.e.
```
# Copying from remote machine with ENV path
scp 192.168.0.1:$HOME $HOME
```
- Instead of
```
# Copying from remote machine with an absolute path
scp 192.168.0.1:/home/myuser /home/otheruser
```
- The matter is that there may not be those directories you want to copy.
- Sometimes the script will be executed even when a command fails. Thus, will affect the rest of the script. Use set -o errexit exit a script when a command fails.
  - nounset flag to exit when your script tries to use undeclared variables.
  - xtrace helps to trace what gets executed (useful for debugging)
```
 #let the script exit if a command fails
 set -o errexit
 set -o nounset
 set -o xtrace
```

Useful Tips

You should prefer absolute paths /home/user/file instead to relative ~/file.
- Use .sh or .bash extension if the file is meant to be included/sourced. Don’t use these extensions on executable script.
- Do not use deprecated style.
  - Define functions as func() { }.
  - Always use [[...]] instead of [].
  - Do not use backticks, use $( ... ).

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codica2 / script-best-practices