Expansion order

Expansion order

[Mads Martin Joergensen]

Hey together,

$ export LS_OPTIONS="-N --color=tty -T 0"
$ alias ls='ls $LS_OPTIONS'
$ ls
/bin/ls: invalid option --
Try `/bin/ls --help' for more information.

How come the zsh is doing the expansion in this case differently from
csh, tcsh, bash and sh?

If it's a configuration option or such, I would be grateful to know. I
looked through the expansion man-pages, but I might have missed it.

-- 
Mads Martin Joergensen, http://mmj.dk
"Why make things difficult, when it is possible to make them cryptic
 and totally illogical, with just a little bit more effort?"
                                -- A. P. J.

Re: Expansion order

[Peter Stephenson]

Mads Martin Joergensen wrote:
> Hey together,
> 
> $ export LS_OPTIONS="-N --color=tty -T 0"
> $ alias ls='ls $LS_OPTIONS'
> $ ls
> /bin/ls: invalid option --
> Try `/bin/ls --help' for more information.
> 
> How come the zsh is doing the expansion in this case differently from
> csh, tcsh, bash and sh?

It's sh_word_split again.  You're using $LS_OPTIONS as a single word and
zsh is obliging.  The error message is confusing.

There are various possibilities:

alias ls="ls $LS_OPTIONS"

is the simplest, but if you want changes in LS_OPTIONS to be reflected
later on you need something else.

alias ls='ls $=LS_OPTIONS'

is the obvious.

More sophisticated:

typeset -xT LS_OPTIONS="-N --color=tty -T 0" ls_options
alias ls='ls $ls_options'

This allows for whitespace characters in the options as long as you
manipulate them through the array ls_options.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR PLC, Churchill House, Cambridge Business Park, Cowley Road
Cambridge, CB4 0WZ, UK                          Tel: +44 (0)1223 692070


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Re: Expansion order

[Bart Schaefer]

On Jan 25,  2:53pm, Peter Stephenson wrote:
} Subject: Re: Expansion order
}
} typeset -xT LS_OPTIONS="-N --color=tty -T 0" ls_options
} alias ls='ls $ls_options'
} 
} This allows for whitespace characters in the options as long as you
} manipulate them through the array ls_options.

Doesn't that need to be

  typeset -xT LS_OPTIONS="-N --color=tty -T 0" ls_options ' '

??  Otherwise it's splitting on colons, not spaces.

Re: Expansion order

[Stephane Chazelas]

On Tue, Jan 25, 2005 at 03:41:50PM +0100, Mads Martin Joergensen wrote:
> Hey together,
> 
> $ export LS_OPTIONS="-N --color=tty -T 0"
> $ alias ls='ls $LS_OPTIONS'
> $ ls
> /bin/ls: invalid option --
> Try `/bin/ls --help' for more information.
> 
> How come the zsh is doing the expansion in this case differently from
> csh, tcsh, bash and sh?
> 
> If it's a configuration option or such, I would be grateful to know. I
> looked through the expansion man-pages, but I might have missed it.
[...]

See question 3.1 in the FAQ
http://zsh.sunsite.dk/FAQ/zshfaq03.html#l17

Even with other Bourne like shells, it's not a good idea to
write it this way as it relies on the current value of IFS.
(if you change IFS, your ls will stop working).

Here, you want LS_OPTIONS to be an array, not a string.

LS_OPTIONS=(-N --color=tty -T 0)
alias ls='ls "${LS_OPTIONS[@]"'

Or if LS_OPTIONS has to be an environment variable, then you'd
better ensure the the right value of IFS is used:

export LS_OPTIONS='-N,--color=tty,-T,0'
ls() {
  (
    IFS=,
    set -f
    exec command ls $LS_OPTIONS "$@"
  )
}

or for zsh, where word splitting and filename generation are
thanksfully not implicit:

export LS_OPTIONS='-N,--color=tty,-T,0'
ls() {
  local IFS=,
  command ls $=LS_OPTIONS "$@"
}

" " (space) is not a good choice of <character> for a
<character> separated list, as it doesn't allows empty elements,
that's why I used "," instead above.

Alternatively, you may consider "LS_OPTIONS" as a part of a
shell command line, so that can have:

LS_OPTIONS='-foo "arg with spaces" -empty ""'
or
LS_OPTIONS='--color="$([ -t 1 ] && echo yes || echo no)"'

Then, you can use it as:

ls() {
  eval "command ls $LS_OPTIONS \"\$@\""
}

Which should work in zsh as well as in POSIX shells.

-- 
Stéphane