inc.sh

echo inc.sh:
if [ "${#BASH_SOURCE[@]}" -le 1 ];then
	echo I am the main script file.
else
	echo I am being called from another file.
fi
func1()
{
   echo env on func1 called from $1:
   set
   echo --------
}
echo env on inc.sh, top-level:
set
echo ----------
func1 inc.sh
echo end of inc.sh

mainscript.sh

echo I am mainscript.sh:
source inc.sh
echo env on mainscript.sh, top-level:
set
echo -----------
func1 mainscript.sh
echo end of mainscript.sh.

Output of revision 4e5932:

[1589039/master]$ bash mainscript.sh  | egrep '^env on|FUNC|BASH_SOURCE'
env on inc.sh, top-level:
BASH_SOURCE=([0]="inc.sh" [1]="mainscript.sh")
env on func1 called from inc.sh:
BASH_SOURCE=([0]="inc.sh" [1]="inc.sh" [2]="mainscript.sh")
FUNCNAME=([0]="func1" [1]="source" [2]="main")
env on mainscript.sh, top-level:
BASH_SOURCE=([0]="mainscript.sh")
mainscript.sh: line 5: -----------: command not found
env on func1 called from mainscript.sh:
BASH_SOURCE=([0]="inc.sh" [1]="mainscript.sh")
FUNCNAME=([0]="func1" [1]="main")
(ehabkost@otherpad:~/tmp/1589039 (ok))
[1589039/master]$ bash inc.sh  | egrep '^env on|FUNC|BASH_SOURCE'
env on inc.sh, top-level:
BASH_SOURCE=([0]="inc.sh")
env on func1 called from inc.sh:
BASH_SOURCE=([0]="inc.sh" [1]="inc.sh")
FUNCNAME=([0]="func1" [1]="main")
(ehabkost@otherpad:~/tmp/1589039 (ok))