topic Re: Command substitution strange behavior? in Operating System - HP-UX

Command substitution strange behavior?

Jesper Sivertsen — Mon, 26 Oct 2009 15:49:37 GMT

Hi there
I have seen a strange behavior i HP-UX that sombody have to explain to mee??

If you try this scipt:
---------------------------------
RES=$(cat <single 'qoute'
double "qoute"
single \'qoute\'
END
)
echo $RES
RES=`cat <single 'qoute'
double "qoute"
single \'qoute\'
END
`
echo $RES
---------------------------------

In HP-UX the result is:
single "qoute" double "qoute" single \'qoute\'
single 'qoute' double "qoute" single \'qoute\'

But in linux bash it is ( as exspected) :
single 'qoute' double "qoute" single \'qoute\'
single 'qoute' double "qoute" single \'qoute\'

Why is there a diffrense in HP-UX between $() and `` ?

Regards Jesper

Re: Command substitution strange behavior?

James R. Ferguson — Mon, 26 Oct 2009 16:08:53 GMT

Hi Jesper:

First, the HP-UX Posix shell ('/usr/bin/sh' or '/sbin/sh') does differ from the 'bash' shell.

I can't offer a reason for the difference you see, however.

It is interesting, though, that if you do:

#!/usr/bin/sh
cat <single 'qoute' double "qoute" single \'qoute\'
END
cat <single 'qoute' double "qoute" single \'qoute\'
END

...you get the expected:

single 'qoute' double "qoute" single \'qoute\'
single 'qoute' double "qoute" single \'qoute\'

...
I'm not sure why you are resorting to collecting a here-doc in a variable and then echoing that variable.

Regards!

...JRF...

Re: Command substitution strange behavior?

OldSchool — Mon, 26 Oct 2009 16:41:35 GMT

For what it may be worth,in ksh on AIX, the result is identical to the HP-UX output the OP posted.

Re: Command substitution strange behavior?

Jesper Sivertsen — Mon, 26 Oct 2009 16:53:52 GMT

This is just an example to show the "problem".
I use the construction to run sqlplus from oracle and get the result in a variable.

Jesper

Re: Command substitution strange behavior?

Bill Hassell — Mon, 26 Oct 2009 23:55:51 GMT

Just to clarify: HP-UX doesn't know anything about quotes and strings and echo. HP-UX is an OS just like Linux. What you are describing is specific to shell programs, and just like Linux and AIX, HP-UX has several shells. As mentioned, the typical shell for HP-UX is the POSIX shell: /usr/bin/sh and not to be confused with the Bourne shell: /usr/old/bin/sh. But you may have been given the Korn shell (aka, ksh-88) for your login on HP-UX, or maybe an optional shell called Bash.

The $() construct is always preferred for modern shells as it can provide unambiguous nesting and is infinitely easier to document properly. The reason is that ' and ` are very, very often typed incorrectly. Read the man page for sh-posix (HP-UX), ksh (any OS) and Bash (any OS) to see the deprecation (obsolete) of grave accents for command substitution.

Bottom line, there are differences between shells. I don't have a clear explanation for the changing of single quotes into double quotes. But as you might imagine, characters that special meaning to the shell will always need extra handling.

Re: Command substitution strange behavior?

Raj D. — Tue, 27 Oct 2009 00:08:26 GMT

Jesper,

Check this out , similar bash WT... page:
you will find more interesting stuff,

http://almirkaric.com/tag/awk/

Hth,

Re: Command substitution strange behavior?

Jesper Sivertsen — Tue, 27 Oct 2009 06:03:40 GMT

I said HP-UX because i se the problem in both posix-shell and ksh.

I know all about shells.
I have worked vith HP-UX and other unixes for more than 15 years and been teathing HP-UX at HP.

That is why i do not understand the difference.

Regards Jesper

Re: Command substitution strange behavior?

Dennis Handly — Tue, 27 Oct 2009 09:46:34 GMT

>I have seen a strange behavior I HP-UX that somebody have to explain to me?

It looks like a bug with new-fangled $() and here documents. Please report it to the Response Center.

RES=$(cat <
It fails even with: <<\END
If you do this, you see the here documented is messed up when it parses the $():
RES=$(cat <<\END > /dev/tty
single 'qoute'
double "qoute"
single \'qoute\'
END
)

>JRF: I can't offer a reason for the difference you see

It's broken. :-(

>It is interesting, though, that if you do:

That doesn't mix the gas with a match.

>Bill: characters that special meaning to the shell will always need extra handling.

And it failed.

Re: Command substitution strange behavior?

Duncan Edmonstone — Tue, 27 Oct 2009 13:11:57 GMT

It's interesting that both sh and ksh are ksh88 type shells, whereas dtksh which is a ksh93 type shell works as expected...

# more ./de.sh
#!/usr/dt/bin/dtksh
RES=$(cat <single 'qoute'
double "qoute"
single \'qoute\'
END
)
echo $RES
RES=`cat <single 'qoute'
double "qoute"
single \'qoute\'
END
`
echo $RES

# ./de.sh
single 'qoute' double "qoute" single \'qoute\'
single 'qoute' double "qoute" single \'qoute\'

Wonder if this is some obscure feature - the POSIX/IEEE standards are almost impossible for joe-admins like me to make sense of, but I wonder if there is something in there that might explain this behaviour...

HTH

Duncan