why is echo different?
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From: Parmenides on 4 Dec 2009 06:31 IFS=: echo $IFS # the result is space echo "$IFS" # the result is : Is there any difference between $IFS and "$IFS"
From: Andrew McDermott on 4 Dec 2009 07:09 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" Also $ aaa="a > b > c > d > e" $ echo $aaa a b c d e $ echo "$aaa" a b c d e 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. Andrew
From: Stephane Chazelas on 4 Dec 2009 07:59 On 2009-12-04, Andrew McDermott <a.p.mcdermott(a)NOSPAM-rl.ac.uk> wrote: > Parmenides wrote: > >> IFS=: >> echo $IFS # the result is space > > a space, or just a blank line? [...] It will depend on the shell. For some shells, IFS is a field separator (zsh, pdksh, ash), and for some, it's a field terminator (bash, AT&T ksh). POSIX is not very clear what it should be (or at least wasn't the last time I checked). So where IFS is a separator, $IFS above is split into "" and "" which echo outputs separated by a space. And where it's a terminator, into just one "". That's something to bear in mind when for instance using IFS=: to split $PATH like variables. -- Stephane
From: Geoff Clare on 4 Dec 2009 09:04 Stephane Chazelas wrote: > It will depend on the shell. For some shells, IFS is a field > separator (zsh, pdksh, ash), and for some, it's a field > terminator (bash, AT&T ksh). POSIX is not very clear what it > should be (or at least wasn't the last time I checked). It was clarified in the 2008 edition. (It says the characters in IFS are used as field terminators.) -- Geoff Clare <netnews(a)gclare.org.uk>
From: Parmenides on 4 Dec 2009 09:40
On 12ÔÂ4ÈÕ, ÏÂÎç8ʱ09·Ö, Andrew McDermott <a.p.mcderm...(a)NOSPAM-rl.ac.uk> wrote: > 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" > > Also > $ aaa="a> b > > c > > d > > e" > > $ echo $aaa > a b c d e > $ echo "$aaa" > a > b > c > d > e > > 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. > > Andrew I see, it means that shell interpretes the content of IFS in terms of its content(:), and the result is null. thanks a lot. |