Unexpected behavior of Bash script: First executes function, afterwards executes alias












5















When I execute the following script



#!/usr/bin/env bash



main() {

    shopt -s expand_aliases 

    alias Hi='echo "Hi from alias"'

    Hi  # Should Execute the alias

    Hi # Should Execute the function

    "Hi"

}



function Hi() {

    echo "Hi from function"

}

main "$@"


Very first time it executes the function and then always executes as alias:



$ . Sample.sh

Hi from function

Hi from function

Hi from function

$ . Sample.sh

Hi from alias

Hi from function

Hi from function


Why is it so?




This does not happen in the following case



#!/usr/bin/env bash



function Hi() {

    echo "Hi from function"

}



shopt -s expand_aliases 

alias Hi='echo "Hi from alias"'

Hi  # Should Execute the alias

Hi # Should Execute the function

"Hi"


Very first time it executes the function and then always executes as alias:



$ . Sample.sh

Hi from alias

Hi from function

Hi from function

$ . Sample.sh

Hi from alias

Hi from function

Hi from function





bash scripting alias function







share|improve this question





























    5















    When I execute the following script



    #!/usr/bin/env bash
    

    
main() {
    
    shopt -s expand_aliases 
    
    alias Hi='echo "Hi from alias"'
    
    Hi  # Should Execute the alias
    
    Hi # Should Execute the function
    
    "Hi"
    
}
    

    
function Hi() {
    
    echo "Hi from function"
    
}
    
main "$@"


    Very first time it executes the function and then always executes as alias:



    $ . Sample.sh
    
Hi from function
    
Hi from function
    
Hi from function
    
$ . Sample.sh
    
Hi from alias
    
Hi from function
    
Hi from function


    Why is it so?




    This does not happen in the following case



    #!/usr/bin/env bash
    

    
function Hi() {
    
    echo "Hi from function"
    
}
    

    
shopt -s expand_aliases 
    
alias Hi='echo "Hi from alias"'
    
Hi  # Should Execute the alias
    
Hi # Should Execute the function
    
"Hi"


    Very first time it executes the function and then always executes as alias:



    $ . Sample.sh
    
Hi from alias
    
Hi from function
    
Hi from function
    
$ . Sample.sh
    
Hi from alias
    
Hi from function
    
Hi from function





    bash scripting alias function







    share|improve this question



























      5












      5








      5








      When I execute the following script



      #!/usr/bin/env bash
      

      
main() {
      
    shopt -s expand_aliases 
      
    alias Hi='echo "Hi from alias"'
      
    Hi  # Should Execute the alias
      
    Hi # Should Execute the function
      
    "Hi"
      
}
      

      
function Hi() {
      
    echo "Hi from function"
      
}
      
main "$@"


      Very first time it executes the function and then always executes as alias:



      $ . Sample.sh
      
Hi from function
      
Hi from function
      
Hi from function
      
$ . Sample.sh
      
Hi from alias
      
Hi from function
      
Hi from function


      Why is it so?




      This does not happen in the following case



      #!/usr/bin/env bash
      

      
function Hi() {
      
    echo "Hi from function"
      
}
      

      
shopt -s expand_aliases 
      
alias Hi='echo "Hi from alias"'
      
Hi  # Should Execute the alias
      
Hi # Should Execute the function
      
"Hi"


      Very first time it executes the function and then always executes as alias:



      $ . Sample.sh
      
Hi from alias
      
Hi from function
      
Hi from function
      
$ . Sample.sh
      
Hi from alias
      
Hi from function
      
Hi from function





      bash scripting alias function







      share|improve this question
















      When I execute the following script



      #!/usr/bin/env bash
      

      
main() {
      
    shopt -s expand_aliases 
      
    alias Hi='echo "Hi from alias"'
      
    Hi  # Should Execute the alias
      
    Hi # Should Execute the function
      
    "Hi"
      
}
      

      
function Hi() {
      
    echo "Hi from function"
      
}
      
main "$@"


      Very first time it executes the function and then always executes as alias:



      $ . Sample.sh
      
Hi from function
      
Hi from function
      
Hi from function
      
$ . Sample.sh
      
Hi from alias
      
Hi from function
      
Hi from function


      Why is it so?




      This does not happen in the following case



      #!/usr/bin/env bash
      

      
function Hi() {
      
    echo "Hi from function"
      
}
      

      
shopt -s expand_aliases 
      
alias Hi='echo "Hi from alias"'
      
Hi  # Should Execute the alias
      
Hi # Should Execute the function
      
"Hi"


      Very first time it executes the function and then always executes as alias:



      $ . Sample.sh
      
Hi from alias
      
Hi from function
      
Hi from function
      
$ . Sample.sh
      
Hi from alias
      
Hi from function
      
Hi from function





      bash scripting alias function




      bash scripting alias function






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 2 days ago







      Nikhil

















      asked 2 days ago









      NikhilNikhil

      310113




      310113






















          1 Answer
          1






          active

          oldest

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          10














          Alias expansion in a function is done when the function is read, not when the function is executed. The alias definition in the function is executed when the function is executed.



          See Alias and functions

          and https://www.gnu.org/software/bash/manual/html_node/Aliases.html



          This means, the alias will be defined when function main is executed, but when the function was read for the first time the alias was not yet defined. So the first time function main will execute function Hi three times.



          When you source the script for the second time, the alias is already defined from the previous run and can be expanded when the function definition is read. When you now call the function it is run with the alias expanded.



          The different behavior occurs only when the script is sourced with . Sample.sh, i.e. when it is run in the same shell several times. When you run it in a separate shell as ./Sample.sh it will always show the behavior of the first run.






          share|improve this answer

























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            1 Answer
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            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            10














            Alias expansion in a function is done when the function is read, not when the function is executed. The alias definition in the function is executed when the function is executed.



            See Alias and functions

            and https://www.gnu.org/software/bash/manual/html_node/Aliases.html



            This means, the alias will be defined when function main is executed, but when the function was read for the first time the alias was not yet defined. So the first time function main will execute function Hi three times.



            When you source the script for the second time, the alias is already defined from the previous run and can be expanded when the function definition is read. When you now call the function it is run with the alias expanded.



            The different behavior occurs only when the script is sourced with . Sample.sh, i.e. when it is run in the same shell several times. When you run it in a separate shell as ./Sample.sh it will always show the behavior of the first run.






            share|improve this answer






























              10














              Alias expansion in a function is done when the function is read, not when the function is executed. The alias definition in the function is executed when the function is executed.



              See Alias and functions

              and https://www.gnu.org/software/bash/manual/html_node/Aliases.html



              This means, the alias will be defined when function main is executed, but when the function was read for the first time the alias was not yet defined. So the first time function main will execute function Hi three times.



              When you source the script for the second time, the alias is already defined from the previous run and can be expanded when the function definition is read. When you now call the function it is run with the alias expanded.



              The different behavior occurs only when the script is sourced with . Sample.sh, i.e. when it is run in the same shell several times. When you run it in a separate shell as ./Sample.sh it will always show the behavior of the first run.






              share|improve this answer




























                10












                10








                10







                Alias expansion in a function is done when the function is read, not when the function is executed. The alias definition in the function is executed when the function is executed.



                See Alias and functions

                and https://www.gnu.org/software/bash/manual/html_node/Aliases.html



                This means, the alias will be defined when function main is executed, but when the function was read for the first time the alias was not yet defined. So the first time function main will execute function Hi three times.



                When you source the script for the second time, the alias is already defined from the previous run and can be expanded when the function definition is read. When you now call the function it is run with the alias expanded.



                The different behavior occurs only when the script is sourced with . Sample.sh, i.e. when it is run in the same shell several times. When you run it in a separate shell as ./Sample.sh it will always show the behavior of the first run.






                share|improve this answer















                Alias expansion in a function is done when the function is read, not when the function is executed. The alias definition in the function is executed when the function is executed.



                See Alias and functions

                and https://www.gnu.org/software/bash/manual/html_node/Aliases.html



                This means, the alias will be defined when function main is executed, but when the function was read for the first time the alias was not yet defined. So the first time function main will execute function Hi three times.



                When you source the script for the second time, the alias is already defined from the previous run and can be expanded when the function definition is read. When you now call the function it is run with the alias expanded.



                The different behavior occurs only when the script is sourced with . Sample.sh, i.e. when it is run in the same shell several times. When you run it in a separate shell as ./Sample.sh it will always show the behavior of the first run.







                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited 2 days ago

























                answered 2 days ago









                BodoBodo

                2,048416




                2,048416






























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