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You can always show the effects of variable quoting with printf.

Word splitting done on var1:

$ var1="hello     world"
$ printf '[%s]\n' $var1
[hello]
[world]

var1 quoted, so no word splitting:

$ printf '[%s]\n' "$var1"
[hello     world]

Word splitting on var1 inside $(), equivalent to echo "hello" "world":

$ var2=$(echo $var1)
$ printf '[%s]\n' "$var2"
[hello world]

No word splitting on var1, no problem with not quoting the $():

$ var2=$(echo "$var1")
$ printf '[%s]\n' "$var2"
[hello     world]

Word splitting on var1 again:

$ var2="$(echo $var1)"
$ printf '[%s]\n' "$var2"
[hello world]

Quoting both, easiest way to be sure.

$ var2="$(echo "$var1")"
$ printf '[%s]\n' "$var2"
[hello     world]

###Globbing problem

Not quoting a variable can lead to glob expansion of its contents:

$ mkdir test; cd test; touch file1 file2
$ var="*"
$ echo $var
file1 file2
$ echo "$var"
*

Note this happens after the variable is expanded only. It is not necessary to quote a glob during assignment:

$ var=*
$ echo $var
file1 file2
$ echo "$var"
*

Use set -f to disable this behaviour:

$ set -f
$ var=*
$ echo $var
*

And set +f to re-enable it:

$ set +f
$ echo $var
file1 file2

You can always show the effects of variable quoting with printf.

Word splitting done on var1:

$ var1="hello     world"
$ printf '[%s]\n' $var1
[hello]
[world]

var1 quoted, so no word splitting:

$ printf '[%s]\n' "$var1"
[hello     world]

Word splitting on var1 inside $(), equivalent to echo "hello" "world":

$ var2=$(echo $var1)
$ printf '[%s]\n' "$var2"
[hello world]

No word splitting on var1, no problem with not quoting the $():

$ var2=$(echo "$var1")
$ printf '[%s]\n' "$var2"
[hello     world]

Word splitting on var1 again:

$ var2="$(echo $var1)"
$ printf '[%s]\n' "$var2"
[hello world]

Quoting both, easiest way to be sure.

$ var2="$(echo "$var1")"
$ printf '[%s]\n' "$var2"
[hello     world]

###Globbing problem

Not quoting a variable can also lead to glob expansion of its contents:

$ mkdir test; cd test; touch file1 file2
$ var="*"
$ printf '[%s]\n' $var
[file1]
[file2]
$ printf '[%s]\n' "$var"
[*]

Note this happens after the variable is expanded only. It is not necessary to quote a glob during assignment:

$ var=*
$ printf '[%s]\n' $var
[file1]
[file2]
$ printf '[%s]\n' "$var"
[*]

Use set -f to disable this behaviour:

$ set -f
$ var=*
$ printf '[%s]\n' $var
[*]

And set +f to re-enable it:

$ set +f
$ printf '[%s]\n' $var
[file1]
[file2]

You can always show the effects of variable quoting with printf.

Word splitting done on var1:

$ var1="hello     world"
$ printf '[%s]\n' $var1
[hello]
[world]

var1 quoted, so no word splitting:

$ printf '[%s]\n' "$var1"
[hello     world]

Word splitting on var1 inside $(), equivalent to echo "hello" "world":

$ var2=$(echo $var1)
$ printf '[%s]\n' "$var2"
[hello world]

No word splitting on var1, no problem with not quoting the $():

$ var2=$(echo "$var1")
$ printf '[%s]\n' "$var2"
[hello     world]

Word splitting on var1 again:

$ var2="$(echo $var1)"
$ printf '[%s]\n' "$var2"
[hello world]

Quoting both, easiest way to be sure.

$ var2="$(echo "$var1")"
$ printf '[%s]\n' "$var2"
[hello     world]

You can always show the effects of variable quoting with printf.

Word splitting done on var1:

$ var1="hello     world"
$ printf '[%s]\n' $var1
[hello]
[world]

var1 quoted, so no word splitting:

$ printf '[%s]\n' "$var1"
[hello     world]

Word splitting on var1 inside $(), equivalent to echo "hello" "world":

$ var2=$(echo $var1)
$ printf '[%s]\n' "$var2"
[hello world]

No word splitting on var1, no problem with not quoting the $():

$ var2=$(echo "$var1")
$ printf '[%s]\n' "$var2"
[hello     world]

Word splitting on var1 again:

$ var2="$(echo $var1)"
$ printf '[%s]\n' "$var2"
[hello world]

Quoting both, easiest way to be sure.

$ var2="$(echo "$var1")"
$ printf '[%s]\n' "$var2"
[hello     world]

###Globbing problem

Not quoting a variable can lead to glob expansion of its contents:

$ mkdir test; cd test; touch file1 file2
$ var="*"
$ echo $var
file1 file2
$ echo "$var"
*

Note this happens after the variable is expanded only. It is not necessary to quote a glob during assignment:

$ var=*
$ echo $var
file1 file2
$ echo "$var"
*

Use set -f to disable this behaviour:

$ set -f
$ var=*
$ echo $var
*

And set +f to re-enable it:

$ set +f
$ echo $var
file1 file2

You can always show the effects of variable quoting with printf.

Word splitting done on var1:

$ var1="hello     world"
$ printf '[%s]\n' $var1
[hello]
[world]

var1 quoted, so no word splitting:

$ printf '[%s]\n' "$var1"
[hello     world]

Word splitting on var inside $():

$ var2=$(echo $var1)
$ printf '[%s]\n' "$var2"
[hello world]
$ var2=$(echo "$var1")
$ printf '[%s]\n' "$var2"
[hello     world]
$ var2="$(echo $var1)"
$ printf '[%s]\n' "$var2"
[hello world]
$ var2="$(echo "$var1")"
$ printf '[%s]\n' "$var2"
[hello     world]

You can always show the effects of variable quoting with printf.

Word splitting done on var1:

$ var1="hello     world"
$ printf '[%s]\n' $var1
[hello]
[world]

var1 quoted, so no word splitting:

$ printf '[%s]\n' "$var1"
[hello     world]

Word splitting on var1 inside $(), equivalent to echo "hello" "world":

$ var2=$(echo $var1)
$ printf '[%s]\n' "$var2"
[hello world]

No word splitting on var1, no problem with not quoting the $():

$ var2=$(echo "$var1")
$ printf '[%s]\n' "$var2"
[hello     world]

Word splitting on var1 again:

$ var2="$(echo $var1)"
$ printf '[%s]\n' "$var2"
[hello world]

Quoting both, easiest way to be sure.

$ var2="$(echo "$var1")"
$ printf '[%s]\n' "$var2"
[hello     world]