How to overcome an incompatibility between the ksh on Linux vs. that installed on AIX/Solaris/HPUX?

Question

I am involved in the process of porting a system containing several hundreds of ksh scripts from AIX, Solaris and HPUX to Linux. I have come across the following difference in the way ksh behaves on the two systems:

#!/bin/ksh
flag=false
echo "a\nb" | while read x
do
    flag=true
done
echo "flag = ${flag}"
exit 0

On AIX, Solaris and HPUX the output is "flag = true" on Linux the output is "flag = false".

My questions are:

• Is there an environment variable that I can set to get Linux's ksh to behave like the other Os's'? Failing that:
• Is there an option on Linux's ksh to get the required behavior? Failing that:
• Is there a ksh implementation available for Linux with the desired behavior?

Other notes:

• On AIX, Solaris and HPUX ksh is a variant of ksh88.
• On Linux, ksh is the public domain ksh (pdksh)
• On AIX, Solaris and HPUX dtksh and ksh93 (where I have them installed) are consistent with ksh
• The Windows NT systems I have access to: Cygwin and MKS NT, are consistent with Linux.
• On AIX, Solaris and Linux, bash is consistent, giving the incorrect (from my perspective) result of "flag = false".

The following table summarizes the systems the problem:

uname -s       uname -r                   which ksh          ksh version                     flag =
========       ========                   =========          ===========                     ======
Linux          2.6.9-55.0.0.0.2.ELsmp     /bin/ksh           PD KSH v5.2.14 99/07/13.2       false
AIX            3                          /bin/ksh           Version M-11/16/88f             true    // AIX 5.3
                                          /bin/ksh93         Version M-12/28/93e             true
SunOS          5.8, 5.9 and 5.10          /bin/ksh           Version M-11/16/88i             true
                                          /usr/dt/bin/dtksh  Version M-12/28/93d             true
HP-UX          B.11.11 and B.11.23        /bin/ksh           Version 11/16/88                true
                                          /usr/dt/bin/dtksh  Version M-12/28/93d             true
CYGWIN_NT-5.1  1.5.25(0.156/4/2)          /bin/ksh           PD KSH v5.2.14 99/07/13.2       false
Windows_NT     5                          .../mksnt/ksh.exe  Version 8.7.0 build 1859...     false    // MKS

Update

After some advice from people in my company we decided to make the following modification to the code. This gives us the same result whether using the "real" ksh's (ksh88, ksh93) or any of the ksh clones (pdksh, MSK ksh). This also works correctly with bash.

#!/bin/ksh
echo "a\nb" > junk
flag=false
while read x
do
    flag=true
done < junk
echo "flag = ${flag}"
exit 0

Thanks to jj33 for the previously accepted answer.

Answer 1

Instead of using pdksh on linux, use the "real" ksh from kornshell.org. pdksh is a blind re-implementation of ksh. kornshell.org is the original korn shell dating back 25 years or so (the one written by David Korn). AIX and Solaris use versions of the original ksh, so the kornshell.org version is usually feature- and bug- complete. Having cut my teeth with SunOS/Solaris, installing kornshell.org ksh is usually one of the first things I do on a new Linux box...