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

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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

edited 12 hours ago

Nikhil

asked 12 hours ago

NikhilNikhil

310112

add a comment | 

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

edited 12 hours ago

Nikhil

asked 12 hours ago

NikhilNikhil

310112

add a comment | 

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

edited 12 hours ago

Nikhil

asked 12 hours ago

NikhilNikhil

310112

#!/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 "$@"

$ . Sample.sh

Hi from function

Hi from function

Hi from function

$ . Sample.sh

Hi from alias

Hi from function

Hi from function

#!/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"

$ . Sample.sh

Hi from alias

Hi from function

Hi from function

$ . Sample.sh

Hi from alias

Hi from function

Hi from function

share|improve this question

edited 12 hours ago

Nikhil

asked 12 hours ago

NikhilNikhil

310112

share|improve this question

edited 12 hours ago

Nikhil

asked 12 hours ago

NikhilNikhil

310112

asked 12 hours ago

NikhilNikhil

310112

asked 12 hours ago

NikhilNikhil

310112

1 Answer
1

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

edited 12 hours ago

answered 12 hours ago

BodoBodo

1,993314

add a comment | 

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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

edited 12 hours ago

answered 12 hours ago

BodoBodo

1,993314

add a comment | 

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

edited 12 hours ago

answered 12 hours ago

BodoBodo

1,993314

add a comment | 

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

edited 12 hours ago

answered 12 hours ago

BodoBodo

1,993314

share|improve this answer

edited 12 hours ago

answered 12 hours ago

BodoBodo

1,993314

answered 12 hours ago

BodoBodo

1,993314

answered 12 hours ago

BodoBodo

1,993314