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From: Parmenides on 4 Dec 2009 09:40
On 12ÔÂ4ÈÕ, ÏÂÎç8Ê±09·Ö, Andrew McDermott <a.p.mcderm...(a)NOSPAM-rl.ac.uk>
> Parmenides wrote:
> > IFS=:
> > echo $IFS # the result is space
> a space, or just a blank line?
> > echo "$IFS" # the result is :
> > Is there any difference between $IFS and "$IFS"
> $ aaa="a> b
> > c
> > d
> > e"
> $ echo $aaa
> a b c d e
> $ echo "$aaa"
> IFS is the internal field separator. When you quote a string with double
> quotes it is a single token. When you don't quote a string it is broken
> into tokens using IFS to identify field separators. IFS normally contains
> the space, tab and newline characters, so in my example 'echo $aaaa'
> becomes 'echo "a" "b" "c" "d" "e"' (ie five arguments) while 'echo "$aaa"'
> contains a single argument - a string on five lines. In your example $IFS
> is either being interpreted as spaces (if indeed it is printing a space),
> or as a string which contains a ':'.
> echo separates its arguments with a space when it prints them.
I see, it means that shell interpretes the content of IFS in terms of
its content(:), and the result is null.
thanks a lot.
From: Seebs on 4 Dec 2009 13:33
On 2009-12-04, Parmenides <mobile.parmenides(a)gmail.com> wrote:
> echo $IFS # the result is space
> echo "$IFS" # the result is :
> Is there any difference between $IFS and "$IFS"
Well, without quotes, the expansion of $IFS is subject to field splitting,
meaning that any characters in $IFS can be replaced by nulls which implicitly
So when you echo $IFS without quotes, it expands to a colon, and is then
separated out into fields, where a field is anything other than colons,
separated by any colons. Which means that it ends up being no arguments
at all. So you're doing echo with no argument.
Copyright 2009, all wrongs reversed. Peter Seebach / usenet-nospam(a)seebs.net
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!
From: Sven Mascheck on 2 Jan 2010 13:09
Geoff Clare wrote:
> Stephane Chazelas wrote:
>> For some shells, IFS is a field separator (zsh, pdksh, ash),
>> and for some, it's a field terminator (bash, AT&T ksh).
>> POSIX [...]
> [...] says the characters in IFS are used as field terminators.
And adding to Stephane's results:
- field separator in earlier posh and earlier ash
- field terminator since posh-0.6.15, since early
(d)ash-0.4.x, ~NetBSD3.1, and in mksh
There are even more variations, probably only important to notice
for such experiments: if the variable contains only characters from
IFS, then one field collapses in mksh and recent posh, or all fields
collapse in Bourne shell and bash-1.05. But such corner cases in
shell tend to be a house of cards, anyway.