Functions in Linux shell (bash)

Define and call a function in Bash

examples/shell/hello_world_function.sh

function hello()
{
    echo "Hello World"
}

echo before
hello
echo after

Return value from shell function

examples/shell/return_from_function.sh

function hello()
{
    echo "hello world"
}

result=$(hello)

echo before
echo $result
echo after

Parameter passing to functions in shell

examples/shell/parameter_passing.sh

function foo()
{
   echo "param: '$1'  param: '$2'"
}

echo before
foo "one" "and two"
echo after

Early return from shell functions

examples/shell/early_return.sh

function foo()
{
   param=$1
   if [ "$param" == "ok" ]
   then
       echo "short"
       return
   fi
      echo "long"
}

foo

foo ok

foo

See also Returning Values from Bash Functions

Empty shell functions

examples/shell/empty.sh

function hello()
{
}

This does not work, but gives this error:

./empty.sh: line 3: syntax error near unexpected token `}'
./empty.sh: line 3: `}'

examples/shell/empty_with_colon.sh

function hello()
{
:
}

A Bash function can be called only after declaration

# qqrq    # ./func.sh: line 2: qqrq: command not found

function qqrq()
{
   echo "hello"
}

qqrq