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Fri, 05 Jan 2024 06:41:44 -0800 (PST) MIME-Version: 1.0 References: <625e7ef5-be1f-4b5d-bb2a-f71634d151cf@eastlink.ca> <3fb34197-be9a-4323-87e0-7052cecf33ea@app.fastmail.com> <3adba5e1-18b6-495e-bcbc-09a554465029@app.fastmail.com> In-Reply-To: From: "Mark J. Reed" Date: Fri, 5 Jan 2024 09:41:32 -0500 Message-ID: Subject: Re: tilde syntax To: Ray Andrews Cc: zsh-users@zsh.org Content-Type: multipart/alternative; boundary="000000000000dbe673060e33d8d9" X-Seq: 29422 Archived-At: X-Loop: zsh-users@zsh.org Errors-To: zsh-users-owner@zsh.org Precedence: list Precedence: bulk Sender: zsh-users-request@zsh.org X-no-archive: yes List-Id: List-Help: , List-Subscribe: , List-Unsubscribe: , List-Post: List-Owner: List-Archive: --000000000000dbe673060e33d8d9 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable When you include the value of a variable (parameter) in a command line, the replacement usually happens too late for the resulting value to participate in other sorts of expansion. For example, if you do `echo *`, you'll get a list of the files in the directory. But if you put the `*` into a variable and echo it: $ asterisk=3D'*' $ echo $asterisk * Likewise, if you have a variable with a space in the value, it's not normally subject to word splitting - if you pass it to a command, that command will get a single argument containing a space, not multiple arguments: $ words=3D'one two' $ printf '%s\n' $words one two (It's worth mentioning that in both of the above cases the behavior of zsh is different from the behavior of bash or ksh, in which the parameter value _is_ subject to further expansion.) You can selectively enable further processing with the `~` and `=3D` modifiers. The `~` means that the result of the variable substitution will be subject to wildcard expansion: $ echo $~asterisk Applications Desktop Documents Downloads Library bin etc git lib src tmp While the `=3D` means it will be subject to word-splitting: $ printf '%s\n' $=3Dwords one two On Thu, Jan 4, 2024 at 9:04=E2=80=AFPM Ray Andrews = wrote: > > On 2024-01-04 17:41, Lawrence Vel=C3=A1zquez wrote: > > Another important part occurs earlier in "Parameter Expansion" and > > can admittedly be hard to find: > > Yes. Seems almost inevitable that with such terse syntax normal search > > culture is going to be frustrating. One must master the shell's jargon. > > I wonder if a syntax index could be contemplated, it would look rather > strange: > > $( > > $(( > > $~ > > ${~ > > if[ > > if[[ > > ... every last construction. > > This is why you can use $~foo instead of ${~foo} sometimes. > > I've noticed that but I don't even try to understand it. I am in awe of > the > > geniuses who wrote the parser. The list of ifs, ands, buts and maybes is > > not for a mere mortal to understand. That's what accretion gets you -- > couldn't > > be otherwise. > > That just refers to the result of the parameter expansion being > > subsequently used as something other than a literal value, if the > context calls for it. > > God knows. It's a steep hill to climb if you're not familiar with it. > Anyway I'm > > at least alert to the issue. > > Tx. > > > --=20 Mark J. Reed --000000000000dbe673060e33d8d9 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
When you include the value of a variable (parameter) in a = command line, the replacement usually happens too late for the resulting va= lue to participate in other sorts of expansion.=C2=A0

= =C2=A0For example, if you do `echo *`, you'll get a list of the files i= n the directory. But if you put the `*` into a variable and echo it:
<= div>
=C2=A0 =C2=A0 $ asterisk=3D'*'
=C2=A0 =C2=A0= $ echo $asterisk
=C2=A0 =C2=A0 *

Likewi= se, if you have a variable with a space in the value, it's not normally= subject to word splitting - if you pass it to a command, that command will= get a single argument containing a space, not multiple arguments:

=C2=A0 =C2=A0 $ words=3D'one two'
=C2=A0= =C2=A0 $ printf '%s\n' $words
=C2=A0 =C2=A0 one two

(It's worth mentioning that in both of the above c= ases the behavior of zsh is different from the behavior of bash or ksh,=C2= =A0in which the=C2=A0parameter value _is_ subject to further expansion.)

You can selectively enable further processing with t= he `~` and `=3D` modifiers.=C2=A0 The `~` means that the result of the vari= able substitution will be subject to wildcard expansion:

=C2=A0 =C2=A0 $ echo $~asterisk
=C2=A0 =C2=A0 Applications= Desktop Documents Downloads Library bin etc git lib src tmp=C2=A0

While the `=3D` means it will be subject to word-splitting= :

=C2=A0 =C2=A0 $ printf '%s\n' $=3Dwords<= /div>
=C2=A0 =C2=A0 one
=C2=A0 =C2=A0 two



=C2=A0 =C2=A0

On Thu, Jan 4,= 2024 at 9:04=E2=80=AFPM Ray Andrews <rayandrews@eastlink.ca> wrote:
=20 =20 =20


On 2024-01-04 17:41, Lawrence Vel=C3=A1zquez wrote:

Another = important part occurs earlier in "Parameter Expansion" and 
can admittedly be hard to find:

Yes.=C2=A0 Seems almost inevitable that with such terse syntax norma= l search

culture is going to be frustrating.=C2=A0 One must master the shell&= #39;s jargon.

I wonder if a syntax index could be contemplated, it would look rather strange:

$(

$((

$~

${~

if[

if[[

... every last construction.=C2=A0 

This is why you can use $~foo instead of ${~foo} sometimes.

I've noticed that but I don't even try to understand it.=C2= =A0 I am in awe of the

geniuses who wrote the parser.=C2=A0 The list of ifs, ands, buts and maybes is

not for a mere mortal to understand.=C2=A0 That's what accretion= gets you -- couldn't

be otherwise.

That jus= t refers to the result of the parameter expansion being 
subsequently used as something other than a literal value, if th=
e
context calls for it.

God knows.=C2=A0 It's a steep hill to climb if you're not fa= miliar with it.=C2=A0 Anyway I'm

at least alert to the issue.=C2=A0

Tx.



    

  





-- 
Ma=
rk J. Reed <mar=
kjreed@gmail.com>


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