topic Re: Changing IFS within a shell script in Operating System - Linux

Changing IFS within a shell script

Michele (Mike) Alberton — Mon, 22 Oct 2012 05:01:21 GMT

Hi !

I need to access different column data files within the same shell script, but they use different field separators so that before doing

while read A B C
do
...
done < file.dat

I need to setup IFS to ";" for instance.

Once done that I would like to reset IFS to the original value (tabs, spaces) but doing

IFS="", or IFS=" " doesn't work like at the beginning.

How can I do that ?

At the beginning running

echo $IFS"+"

gives me back

$+

so that I thought the default value was "", but it's not that easy ... sigh.

Thanks in advance !

Cheers,

Mike

P.S. This thread has been moved from HP-UX > General to HP-UX > languages - HP Forums moderator

Re: Changing IFS within a shell script

john korterman — Thu, 20 Nov 2003 03:59:15 GMT

Hi,
have you tried the simple approach; save the original value at the very beginning of your script:
SAVE_IFS="$IFS"
and then restore the value later...

IFS="$SAVE_IFS"

regards,
John K.

Re: Changing IFS within a shell script

Massimo Bianchi — Thu, 20 Nov 2003 03:59:52 GMT

Ohters will tell you better trick and solution, mine is a workaround...

at the beginning of the script

SAVE_IFS=$IFS

...
work as needed
...

at the end of the script.

IFS=${SAVE_IFS}

Massimo

Re: Changing IFS within a shell script

Stefan Farrelly — Thu, 20 Nov 2003 04:04:28 GMT

The default value for IFS is a newline, not a null. In any posix shell I get;

echo "A${IFS}B"
A
B

Re: Changing IFS within a shell script

Michele (Mike) Alberton — Thu, 20 Nov 2003 04:05:12 GMT

That's why I love this FORUM !

Simply great, thanks to both, well earned !

Cheers,

Mike

Re: Changing IFS within a shell script

David Totsch — Fri, 21 Nov 2003 14:01:51 GMT

You could also do it like this:

(
IFS="${IFS}|"
while read A B C
do
.
.
.
done
)

The parenthesis set-up a sub-environment. You can even cd(1) within the parenthesis and outside them go back to where you were w/o having to record where you came from.

Enjoy,
-dlt-

Re: Changing IFS within a shell script

Michele (Mike) Alberton — Fri, 21 Nov 2003 14:09:02 GMT

Thanks David,

I implemented the backup and restore approach, but definitely this looks very elegant.
I'm still wondering if there's any chance to reset the value of IFS, without the need of restoring it through an external var.Ã¹
I odumped the value and it really looks a NULL, but it is not...

Again, thanks !

Mi

Re: Changing IFS within a shell script

Michael Schulte zur Sur — Fri, 21 Nov 2003 14:37:51 GMT

Hi Mike,

thats just, what Davids approach does.
() creates a subenvironment, which ceases to exist after ), so you can do to IFS all you want and no need to restore it.

right Dave?

Michael

Re: Changing IFS within a shell script

curt larson_1 — Fri, 21 Nov 2003 14:44:35 GMT

the default value of IFS is the space character, the tab character, and the newline
IFS=" \t\n"

do an print $IFS | vis -n to see the characters

Re: Changing IFS within a shell script

Michele (Mike) Alberton — Fri, 27 Jan 2006 13:21:22 GMT

Usage of parenthesis to group the set of instructions using the new IFS worked ok.
Thanks to all those who helped me in this