Bash Function Definition and Invocation

my_func() {
	echo "my function is working"
}
myfunc

• the similar to python, with (), but there is no ;, and the function need to start with {}
• it can also be defined as function myfunc() {}
• to call a function, write out the function, but without the ()
  Important: function name CANNOT be a built-in function eg. time, date, ls

Function with Variables

my_func() {
        echo "scale=4; $1/$2+($3-$4)" | bc
        for i in $*; do echo "$i-0.5" |bc ; done
}
my_func 1 4 1 0.667 5# 0.5830
# also echo out all the input and minux by -0.5

• $1,2,3 indicates positional arguments and are ordered
• if there are more arguments in a function that parameters these arguments will be ignored
• however, $* consists of all the arguments that is passed into the function

Function Return

my_func() {
    echo $(( $1+10 ))
}
my_func 10 # returns 20
[ $(my_func 20) == 30 ] && echo "return 30" || echo "return not 30"

• using echo will return the output of the function for further testing
• for functions, it’s different than variable, if it returns something, it needs to be enclosed in $() when trying to evaluate with test function
  Another way using exit code

new_func() {
	return 20
}
new_func; echo $?

• return is only used for exit codes not returning values

Command Line
A bash function can be sourced

source myscript.sh
my_func args
./myscript.sh func1 args

• after it’s sourced, the functions are available to use in command line
  Using "$@" after a function allow the function to be called in the cli with arguments
  Using *args and **kwargs in Bash Functions

Unlike Python, Bash does not have *args and **kwargs syntax. Instead, Bash functions receive all arguments as positional parameters ($1, $2, …, $N). To access all arguments, use $@ or $*. There is no direct equivalent to Python’s keyword arguments (**kwargs), as Bash only supports positional arguments.

Example:

my_func() {
    echo "All arguments: $@"
    for arg in "$@"; do
        echo "Argument: $arg"
    done
}
my_func 1 2 3 "foo" "bar"

• $@ expands to all arguments as separate words.
• $* expands to all arguments as a single word.