How can I run a function from a script in command line?

If the script only defines the functions and does nothing else, you can first execute the script within the context of the current shell using the source or . command and then simply call the function. See help source for more information.

The following command first registers the function in the context, then calls it:

. ./myScript.sh && function_name

Well, while the other answers are right - you can certainly do something else: if you have access to the bash script, you can modify it, and simply place at the end the special parameter "$@" - which will expand to the arguments of the command line you specify, and since it's "alone" the shell will try to call them verbatim; and here you could specify the function name as the first argument. Example:

$ cat test.sh
testA() {
  echo "TEST A $1";
}

testB() {
  echo "TEST B $2";
}

"$@"


$ bash test.sh
$ bash test.sh testA
TEST A 
$ bash test.sh testA arg1 arg2
TEST A arg1
$ bash test.sh testB arg1 arg2
TEST B arg2

For polish, you can first verify that the command exists and is a function:

# Check if the function exists (bash specific)
if declare -f "$1" > /dev/null
then
  # call arguments verbatim
  "$@"
else
  # Show a helpful error
  echo "'$1' is not a known function name" >&2
  exit 1
fi