shell curly braces with double quotes does not expand as i expect

[yukihisa]

hello people,

I'm really new here this is the first try to get some knowledge here.

I have a littele question.
"echo {1,2}" does expands 1 and 2.
so does "echo "`echo {1,2}`"".

But when I do it with double quotes which is "echo "{1,2}"" it doesn't expand at all.

why does this happen? I have read man for bash but could not get any clue.

Please tell me if you have any idea.

Regards,

Yuki

-- the output i see --
sh-3.2# echo {1,2}
1 2
sh-3.2# 
sh-3.2# echo "`echo {1,2}`"
1 2
sh-3.2# 
sh-3.2# echo `echo {1,2}`
1 2
sh-3.2# 
sh-3.2# echo "{1,2}"
{1,2}
sh-3.2#

----------------------------

[tornow]

In everyday speech or writing, when we "quote" a phrase, we set it apart and give it special meaning. In a Bash script, when we quote a string, we set it apart and protect its literal meaning.

From here:
Quoting
But there sure is a better explanation.
Quoting rules in Bash are anything but easy or clear. Double or single quotes, variables involved: yes or no, and so on.

In general: If you use variables you will want to use double quotes to avoid trouble with spaces.

Hoping i am not plain wrong.

[yukihisa]

hello tornow,

Thank you for your reply.
I see using double quotes (") is not required in this term because it doesn't contain
any white spaces which is {1,2}.

What i was trying to do is to expand some items in shell script like bellow.

-----------------------

#!/bin/bash

COMMAND="/bin/rm"
TARGET="{/tmp/test1,/tmp/test2}"

${COMMAND} ${TARGET}

-----------------------

This is just a example what i want to do, i know we can do the same with "for".
i am just curious about this.

${COMMAND} {/tmp/test1,/tmp/test2} does work.

but
${COMMAND} ${TARGET} does not work, the curly braces does not expand its content.

I'm guessing this is caused because the value for $TARGET has been set which should be {/tmp/test1,/tmp/test2} and it doesn't expand afterward because the value is being treated as a value in $TARGET, not the shell thing, without the shell special meanings.


ummm....

I know sometimes there are things that I do not need to know the exact reason why things work like they do.

Thanks anyway!!

[tornow]

In your example i would create an array and loop over it:

#!/usr/bin/env bash

FILES=(file0.txt file1.txt file2.txt)
for i in "${FILES[@]}"
do
    echo "$i"
done 
exit 0

The curly brackets i use from the command-line only:

mv /etc/X11/{xorg.conf,xorg.conf_backup}

where it, expansion, does work