assign local variable from function in linux bash a new value

Question

I have a linux bash script with a function:

myfunctiona ()  {   local MYVAR1="one"   local MYVAR2="two"   echo $MYVAR1   # The line beneath is the line in question!   local MYVAR1=$MYVAR1$MYVAR2        } 

When I want to give the LOCAL variable MYVAR1 in the function myfunctiona a new value, do I have to write

local MYVAR1=$MYVAR1$MYVAR2 

or can I also write

MYVAR1=$MYVAR1$MYVAR2 

With the second line without "local" do I create a global variable with the same name?

Answer 1

Once you've defined a local variable you can assign it normally, like this:

#!/bin/bash  myfunctiona ()  {   local MYVAR1="one"   local MYVAR2="two"   echo $MYVAR1   # The line beneath is the line in question!   local MYVAR1=$MYVAR1$MYVAR2       MYVAR1="FOO"   echo $MYVAR1    }  myfunctiona echo "global" $MYVAR1 

which gives the output:

one FOO global 

• As you can see attempting to access the variable from global scope returns null

HTH

Answer 2

The correct way to do it would be:

MYVAR1="${MYVAR1}${MYVAR2}" 

The braces are usually used when you concatenate variables. Use quotes.

The variable is still local since you reassigned its value within the scope of the function. An example:

#!/usr/bin/env bash  _myFunction() {     local var_1="one"     local var_2="two"     local -g var_3="three" # The -g switch makes a local variable a global variable     var_4="four" # This will be global since we didn't mark it as a local variable from the start      var_1="${var_1}${var_2}"      echo "Inside function var_1=${var_1}"     echo "Inside function var_2=${var_2}"     echo "Inside function var_3=${var_3}"     echo "Inside function var_4=${var_4}" }  _myFunction  echo "Outside function var_1=${var_1}" echo "Outside function var_2=${var_2}" echo "Outside function var_3=${var_3}" echo "Outside function var_4=${var_4}" 

This results in:

$ ./script Inside function var_1=onetwo Inside function var_2=two Inside function var_3=three Inside function var_4=four Outside function var_1= Outside function var_2= Outside function var_3=three Outside function var_4=four