Re: problem under cygwin with sh, bash, ksh

[Dirk Fassbender <dirk dot fassbender at arcor dot de>]

VÃclav Haisman schrieb:
> Hubert Samm wrote, On 6.3.2009 14:26:
> > Hi All...  I've searched and found nothing....  this script runs just fine on 
> > AIX, Solaris, and Linux, but under cygwin, the array VALUE prints only 
> > blanks.. has anyone else run into this... I've tried a bunch of different 
> > things around typecast, etc, but it looks like VALUE is local in the table_it 
> > function...  any thoughts???
> > [...]
> Have you tried debugging it using the -x switch to see what is going on?
> Simple test case of setting VALUE[0]=$1 and then echoing "${VALUE[0]}" does
> print what I give it, using bash.
>
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> VH
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This is a problem with portable script programming between different shells.
Some explanations:

Shell Versions used:
AIX uses as the default  sh  shell a  ksh Version 88.
HP-UX uses as the default  sh   shell a  ksh Version 88.
Solaris uses as the default  sh  shell a non posix compatible shell.
The ksh on Solaris is mostly a Version 88, opensolaris uses a ksh 
Version 93.
Linux uses as the default  sh  shell a bash.
Older Linux versions uses a  pdksh  as a replacement for the ksh shell.
Newer Linux versions uses a  ksh    Version 93.
Cygwin uses as the default  sh  shell a bash
Cygwin uses the a  pdksh  as a replacement fir the ksh shell.

Setting variables and sub shells.
If you set a variable in a sub shell, this variable usable in the 
calling shell. You can execute commands in a sub shell with the 
following syntax  (list).

The different shell executed the commands in a pipe in a different 
manner. The shells uses internally sub shells to execute the different 
commands of a pipe line.


           command1  |  command2  |  command3
is executed in this order in the different shells.
bash   :   command1  | (command2) | (command3)
pdksh  :   command1  | (command2) | (command3)
ksh    :  (command1) | (command2) |  command3

So only in a ksh it is possible to set a variable in the last command of 
a pipeline and uses this variable later in the shell script.

A short example script for bash, pdksh and ksh is attached.
It includes a in all 3 shell working solution at the end.

So the solution for your problem is to use a ksh  version 93 on cygwin 
or rewrite your code more portable.
You can download a version of ksh version 93 from http://www.kornshell.com/

Regards
Dirk




















#!/bin/ksh
#!/bin/bash
#!/bin/pdksh

TESTVAR="VALUE befor setting a differend value in a sub shell"
echo "OUTSIDE of sub shell. Value of \${TESTVAR} before setting a differend value in a sub shell: ${TESTVAR}"
( 
  echo "INSIDE of sub shell. Value of \${TESTVAR} before setting a differend value in a sub shell: ${TESTVAR}"
  TESTVAR="NEW VALUE set inside a sub shell"
  echo "INSIDE of sub shell. Value of \${TESTVAR} after setting a differend value in a sub shell: ${TESTVAR}"
)
echo "OUTSIDE of sub shell. Value of \${TESTVAR} before setting a differend value in a sub shell: ${TESTVAR}"

echo
echo

TESTVAR="Value before READ in PIPE"
echo "Value of \${TESTVAR} before READING in a pipe: ${TESTVAR}"
echo "New value to READ in PIPE" | { read TESTVAR; echo "This is the value of \${TESTVAR} during execution of the read part of the pipe : ${TESTVAR}"; }
echo "Value of \${TESTVAR} after READING in a pipe: ${TESTVAR}"

echo
echo

TESTVAR="Value before portable while read loop"
echo "Value of \${TESTVAR} before READING portable in a while read loop: ${TESTVAR}"a
i=0
while read TESTVAR; do
    echo "Value of \${TESTVAR} after READING portable in a while read loop: ${TESTVAR}"
    i=$(( i + 1 ))
	READVALUE[${i}]=${TESTVAR}
done <<END
First line to read in the while read loop
Second line to read in the while read loop
END
echo "Value of \${TESTVAR} after the end of the while read loop: ${TESTVAR}"
echo "Value of \${READVALUE[1]} after the end of the while read loop: ${READVALUE[1]}"
echo "Value of \${READVALUE[2]} after the end of the while read loop: ${READVALUE[2]}"

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