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# Script version global variable. Edit this whenever changes are made.
__ADVANCED_BASH_VERSION__="step_01"

# Later, the value of this environment variable is referencesreferenced 
# by prefixing the name with the dollar sign ( $ )
echo "Current script version is: $__ADVANCED_BASH_VERSION__"

# or enclosed in ${ }
echo "Current script version is: ${__ADVANCED_BASH_VERSION__}"

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When defining or evaluating environment variables there's also a difference between enclosing the value in double quotes ( "$foo" ) or single quotes ( '$foo' ) – see Intro Unix: Quoting in the shell (Intro Unix).

Example:

myvar="some text"
echo "$myvar"
echo '$myvar'

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And in bash, arguments passed to both scripts and functions are not enclosed in parentheses, as is the case in most many programming languages.

Example:

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Since there is no formal argument list, it is good practice to copy function arguments into local variables with names suggesting their role. (e.g. local txt1=$1). The local keyword specifies that the variable scope is only within the function body – it is not visible to the caller or to called functions.

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Dispatching to the appropriate function is done using a case/esac block. The case argument string ("$CMD$CMD") is matched against each clause using the clause text before the right parenthesis ")". The double-semicolon ";;" terminates each case clause, including the default case "*".

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function myfn() { echo "arg 1: $1"; echo "arg 2: $2"; echo "all args: $@"; }
myfn foo bar baz wonk
myfn foo "bar baz" wonk
myfn "foo bar" baz wonk

As described in Intro Unix: Quoting in the shell, this is the main function of both single and double quotes – to group text containing whitespace into one item.

Running the step_01.sh script

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