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# 1  
Old 02-06-2014
Dot sourcing differences in ksh, AIX vs Linux vs Solaris
Why does dot sourcing of ksh functions behave so differently between AIX, Solaris, and Linux? How can I make Linux behave the way I want in the test I show below?

I have a library of interdependent functions I have developed and use in ksh in AIX. They also run in Solaris. Now I am migrating them to Linux. They aren't working properly in Linux. I have devised a test to illustrate the differences. I am looking for an explanation of the behavior, particularly in Linux, and how I can resolve it to be like Solaris (which would be OK) or like AIX (which would be ideal).

Test 1 below is the behavior I like. Test 2 is OK. Test 3 is the one I don't understand and need to fix.

I start by creating this file that contains the "MyFun" function definition in a directory that is on my PATH:
Code:
$ cat MyFun
#! /bin/ksh
print -- "In file MyFun, before def of function MyFun. PID=$$, system=$( uname -rsv )"
function MyFun
{
print -- "In function MyFun. PID=$$, system=$( uname -rsv )"
return $(( $# % 128 )) #number of arguments mod 128
}
print -- "In file MyFun, after def of function MyFun. PID=$$, system=$( uname -rsv )"

The contents above are stored in file "MyFun", which does NOT require execute permissions:
Code:
$ ls -l MyFun | xargs echo | cut -d ' ' -f 1,9 
-rw-r--r-- MyFun

############
TEST 1: run in AIX
(first install MyFun from above into a directory in your PATH, then cd to that directory)

Here when the file is dot sourced a second time, NONE of it executes. The system is caching the dot-sourcing operation, so if this function is shared by several other functions that dot source it and all are used in a script, it only executes once.

The important thing is that the inner part of the function never executes when the file is dot sourced (the function itself doesn't get called during dot sourcing). In this case the behavior is like an import (not include) statement, and is the behavior I want:
Code:
$ #dot source the file first time
$ . MyFun
In file MyFun, before def of function MyFun. PID=8908866, system=AIX 3 5
In file MyFun, after def of function MyFun. PID=8908866, system=AIX 3 5
$ #call the function after dot sourcing
$ MyFun
In function MyFun. PID=8908866, system=AIX 3 5
$ #dot source the file a second time
$ . MyFun
#(there is no output from the command above).

############
TEST 2: run in Solaris (first install MyFun from above)
(first install MyFun from above into a directory in your PATH, then cd to that directory)

Here when the file is dot sourced a second time, the file executes again just like the first time. The system is re-executing the entire file each time it is dot sourced, so if this function is shared by several other functions that dot source it and all are used in a script, the file re-executes every time and the function itself is redundantly redefined each time.

The important thing is that the inner part of the function still never executes when the file is dot sourced (the function itself doesn't get called during dot sourcing). This behaves like an include (not import) statement, and is inefficient compared to test 1, but still works:
Code:
$ #dot source the file first time
$ . MyFun
In file MyFun, before def of function MyFun. PID=29760, system=SunOS 5.10 Generic_141444-09
In file MyFun, after def of function MyFun. PID=29760, system=SunOS 5.10 Generic_141444-09
$ #call the function after dot sourcing
$ MyFun
In function MyFun. PID=29760, system=SunOS 5.10 Generic_141444-09
$ #dot source the file a second time
$ . MyFun
In file MyFun, before def of function MyFun. PID=29760, system=SunOS 5.10 Generic_141444-09
In file MyFun, after def of function MyFun. PID=29760, system=SunOS 5.10 Generic_141444-09

############
TEST 3: run in Linux (first install MyFun from above into a directory in your PATH, then cd to that directory)

Here when the file is dot sourced a second time, the FUNCTION BODY executes even though I don't want to CALL it.

The problem here is that the inner part of the function executes when the file is dot sourced after the first time (the function itself gets called during subsequent dot sourcing operations). I do not understand this behavior and it is harmful:
Code:
$ #dot source the file first time
$ . MyFun
In file MyFun, before def of function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
In file MyFun, after def of function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
$ #call the function after dot sourcing
$ MyFun
In function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
$ #dot source the file a second time
$ . MyFun
In function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011

Last edited by charles_n_may; 02-06-2014 at 06:29 PM.. Reason: clarifying explanations
# 2  
Old 02-06-2014
I think you're using a non-portable function declaration... In some shells that would be a syntax error. This syntax works in any Bourne shell that supports functions AFAIK:

Code:
function () {
        contents
}

This User Gave Thanks to Corona688 For This Post:
rbatte1
# 3  
Old 02-06-2014
RedHat
I want the behavior given by using the function keyword as it is indeed different from that using the parentheses. I use the difference (ksh functions defined with function have their own function environment and my code relies heavily on that isolation, particularly for logging the name of the function, $0, being called), and I am not really interested in bash compatibility.

However I did notice that if I use corrected bash syntax I get basic compatibility with the Solaris test (regardless of whether the curly brace is on the same line as the parens):

Code:
$ cat MyFun
#! /bin/ksh
print -- "In file MyFun, before def of function MyFun. PID=$$, system=$( uname -rsv )"
MyFun() {
print -- "In function MyFun. PID=$$, system=$( uname -rsv )"
return $(( $# % 128 )) #number of arguments mod 128
}
print -- "In file MyFun, after def of function MyFun. PID=$$, system=$( uname -rsv )"

Running the above in Linux:
Code:
$ . MyFun
In file MyFun, before def of function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
In file MyFun, after def of function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
$ MyFun
In function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
$ . MyFun
In file MyFun, before def of function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
In file MyFun, after def of function MyFun. PID=37604, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011

The above still isn't acceptable because using the bash sytax, the function's name is not stored in $0 inside the function body when it executes.
Last edited by charles_n_may; 02-06-2014 at 07:16 PM..
# 4  
Old 02-06-2014
Are you sure your Linux' /bin/ksh is really a ksh and not a link to somewhere else?
# 5  
Old 02-06-2014
For my linux host:

Code:
 
$ which ksh
/bin/ksh

$ print ${.sh.version}
Version JM 93t+ 2010-06-21

# 6  
Old 02-06-2014
ksh supports two types of function definition syntax:
Code:
 name() {body;}

result in a Posix style function. No scoping allowed and thus side-effects abound.
Code:
function name {body;}

Standard ksh functions. You can define local variables and have local signals.

With newer version ksh (such as inhabit linux) the . command has been expanded. In addition to sourcing a filename, the argument to the . command can now be a function. This invokes the function forcing it into local scope. This new feature is killing you. One idea is to name the file and the function it contains differently. . MyFunc.def would define a function called MyFunc. Then you have no name collision. Another idea is to use a pathname:. ./MyFunc.

The behavior you describe on AIX is strange. I can't explain that. But I think I could induce it. Try this:
Code:
if [[ $MyFunDef != "true" ]] ; then
        export MyFunDef="true"
        #! /bin/ksh  this line serves no purpose in a sourced file
        print -- "In file MyFun, before def of function MyFun. PID=$$, system=$( uname -rsv )"
        function MyFun
        {
        print -- "In function MyFun. PID=$$, system=$( uname -rsv )"
        return $(( $# % 128 )) #number of arguments mod 128
        }
        print -- "In file MyFun, after def of function MyFun. PID=$$, system=$( uname -rsv )"
fi

Last edited by Perderabo; 02-06-2014 at 07:37 PM..
These 3 Users Gave Thanks to Perderabo For This Post:
charles_n_may drl vgersh99
# 7  
Old 02-06-2014
Well now this is promising. I will look into that in more detail overnight. Simply using the dot - dot-slash notation also makes the linux version at least compatible with Solaris. I modified the function slightly to show the value of $0 inside it here:

Code:
 
$ cat MyFun
#! /bin/ksh
print -- "In file MyFun, before def of function MyFun. PID=$$, system=$( uname -rsv )"
function MyFun {
  print -- "In function MyFun. \$0=$0. PID=$$, system=$( uname -rsv )"
  return $(( $# % 128 )) #number of arguments mod 128
}
print -- "In file MyFun, after def of function MyFun. PID=$$, system=$( uname -rsv )"

Running in linux:

Code:
$ . ./MyFun
In file MyFun, before def of function MyFun. PID=19620, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
In file MyFun, after def of function MyFun. PID=19620, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
$ MyFun
In function MyFun. $0=MyFun. PID=19620, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
$ . ./MyFun
In file MyFun, before def of function MyFun. PID=19620, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011
In file MyFun, after def of function MyFun. PID=19620, system=Linux 2.6.32-220.el6.x86_64 #1 SMP Wed Nov 9 08:03:13 EST 2011



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