unexpected result from sh script with `date`

[Erik Trulsson]

On Fri, Feb 02, 2007 at 01:48:31PM +0100, J65nko wrote:
> On 2/2/07, Tigger <tigger at lvlworld.com> wrote:
> >Hello, the following simply sh script is outputting unexpected results.
> >Any idea why?
> >
> >--script--
> >
> >#!/bin/sh
> >
> >started=`date`
> >
> >echo "Started at: $started"
> >echo "Finished  : "`date`
> >exit
> >
> >--output--
> >
> >Started at: Fri Feb  2 22:13:51 EST 2007
> >Finished  : Fri Feb 2 22:13:51 EST 2007
> >
> >--problem--
> >
> >Between 'Feb' and '2', there is two spaces on the 'Started at' line,
> >however the 'Finished' one only has 1 space.
> >
> >I know this sounds picky, but I was not expecting this at all.
> >
> >uname -a
> >FreeBSD piglet 6.2-STABLE FreeBSD 6.2-STABLE #0: Fri Jan 19 04:13:20 EST
> >2007     tigger at piglet:/usr/obj/usr/src/sys/PIGLET  i386
> 
> The same on OpenBSD here (ksh)
> OpenBSD 4.0-current (GENERIC) #1194: Thu Nov  2 16:32:12 MST 2006
>    deraadt at i386.openbsd.org:/usr/src/sys/arch/i386/compile/GENERIC
> 
> It seems to depend whether  the command substitution is within the
> quote-delimited string,   for 'echo' or outside that string, in other
> words on its own.
> ------- script----------
> #!/bin/sh
> 
> started=$(date)
> 
> echo "\$started within \" delimited string for echo"
> echo "Started at: $started"
> echo "Command substitution \$(date) within \" delimited string for echo"
> echo "Finished  : $(date)"
> echo "Command substitution \$(date) outside \" delimited string for echo"
> echo "Finished  : "$(date)
> echo "Command substitution \`date\` outside \" delimited string for echo"
> echo "Finished  : "$(date)
> -----------------------------------
> Output:
> -------------------
> $started within " delimited string for echo
> Started at: Fri Feb  2 13:46:07 CET 2007
> Command substitution $(date) within " delimited string for echo
> Finished  : Fri Feb  2 13:46:07 CET 2007
> Command substitution $(date) outside " delimited string for echo
> Finished  : Fri Feb 2 13:46:07 CET 2007
> Command substitution `date` outside " delimited string for echo
> Finished  : Fri Feb 2 13:46:07 CET 2007
> ---------------------------------------
> Embedded inside the string there are two spaces between Feb and the 2,
> as "stand-alone" there is only one space.
> 
> Strange indeed ;)

Not strange at all if think about how 'echo' works and how the arguments are
passed to it.
If you do a  
  echo `date` 
then echo will be passed 6 arguments ('Fri' 'Feb' '2' '13:46:07' 'CET' '2007')
and print them with a single space between each of them.
If you do a 
  echo "`date`"
then echo will be passed only a single argument ('Fri Feb  2 13:46:07 CET 2007')
which will be printed unmodified.

As another example compare the outputs of
  echo  a  b c
and
  echo "a  b c"




-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at student.uu.se