[SOLVED] How differentiate functions with same name in separate shells

app4dxh · 01-27-2016, 10:00 AM

Hi, here is my question.
I have a parent shell that will call a function in subshell and return back to the parent.
The next line of code will call a function in the parent (This function name ALSO exits in the subshell)
It seems the function in the subshell is getting executed.
For simplicity, I created small test shells to play around with:
1. Parent shell - calling.sh
DUPL_FUNC()
{
echo "In DUPL_FUNC in calling.sh"
}

. func.sh FUNC_FUNC abc

DUPL_FUNC
exit 0

2. subshell - func.sh:
DUPL_FUNC()
{
echo "In DUPL_FUNC in func.sh"
}

FUNC_FUNC()
{
ARG1=$1
echo "in FUNC_FUNC in func.sh"
}

FUNC_NAME=$*
$FUNC_NAME
return 0

3. Execute:
./calling.sh
in FUNC_FUNC in func.sh
In DUPL_FUNC in func.sh

I want the echo from DUPL_FUNC to come from the parent, calling.sh like such:
In DUPL_FUNC in calling.sh

Thanks if you can help :-)

Keith Hedger · 01-27-2016, 10:43 AM

Basically you can't, a subshell can't know anything about a parent process except for any environment variable's exported from the parent and if the child alters a variable the parent can't know the new value, if the child exports a variable the parent can't know the value, though any children of the child will know about the newly exported variable.

If you need to share functions use the "." or include statements, if you then need to do different things in the function depending on the calling process just pass an argument to the function, either the pid of the calling process or something similar.

Please also use code tags to surround your code as it make it easier to read.

Keith Hedger · 01-27-2016, 10:45 AM

Small example, two file called proc1 and proc2 in the same folder, proc1

Code:

#©keithhedger Wed 27 Jan 16:33:58 GMT 2016 kdhedger68713@gmail.com

testfuncproc1 ()
{
	echo "testfunc from proc1"
}

testfuncproc1
./proc2

proc2

Code:

#!/bin/bash -e

#©keithhedger Wed 27 Jan 16:34:09 GMT 2016 kdhedger68713@gmail.com
testfuncproc2 ()
{
	echo "testfunc from proc2"
}

testfuncproc1
./proc2

Execute proc1

Code:

keithhedger@LFSHal:/tmp-> ./proc1
testfunc from proc1
./proc2: line 9: testfuncproc1: command not found

As you can see proc2 ( the child ) cant see the parents function defs.

grail · 01-27-2016, 10:48 AM

Quote:

I have a parent shell that will call a function in subshell and return back to the parent.

This is not what you did.

Code:

. func.sh FUNC_FUNC abc

Here you are sourcing (by the use of '.') func.sh, which if it has the same named function as the calling script, will overwrite it, so now only DUPL_FUNC from func.sh exists.

To make it run in a subshell, simply call it:

Code:

func.sh FUNC_FUNC abc

Of course if not in your PATH you will need to give the path to the script.

I didn't test this, but i am pretty sure

app4dxh · 01-27-2016, 04:48 PM

Thank You! Made suggested changes, working as I expected.

GazL · 01-28-2016, 12:46 PM

Quote:

Originally Posted by Keith Hedger

Code:

keithhedger@LFSHal:/tmp-> ./proc1
testfunc from proc1
./proc2: line 9: testfuncproc1: command not found

As you can see proc2 ( the child ) cant see the parents function defs.

Though in bash you can export functions and they're passed to the children through the environment (which was what led to the 'Shellshock' vulnerability thingy a while back).

Code:

test@ws2:/tmp$ cat proc1
#!/bin/bash

testfunc1() {
  echo "testfunc1 from proc1"
}

testfunc1

export -f testfunc1

./proc2
test@ws2:/tmp$ cat proc2
#!/bin/bash

testfunc1

test@ws2:/tmp$ ./proc1
testfunc1 from proc1
testfunc1 from proc1
test@ws2:/tmp$

Exporting functions is a bash specific extension however. Traditional bourne shell and ksh had the good sense not to provide this "feature". When I remember, I make a point of using "#!/bin/bash -p" to disable it.

Keith Hedger · 01-28-2016, 02:09 PM

Quote:

Originally Posted by GazL

Though in bash you can export functions and they're passed to the children through the environment (which was what led to the 'Shellshock' vulnerability thingy a while back).
...
Exporting functions is a bash specific extension however. Traditional bourne shell and ksh had the good sense not to provide this "feature". When I remember, I make a point of using "#!/bin/bash -p" to disable it.

You are of course quite correct I forgot about the -f switch to export, but as you say is non statndard.