linux bash dictionary check if empty
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How to check if a dictionary (associative array) is empty? I just declare one using declare -A dict. I want to know if it is just declared but not have any key.
bash shell-script associative-array
edited Dec 7 at 10:14
Kusalananda
120k16225369
asked Dec 7 at 9:56
focus zheng
14
add a comment |
up vote
0
down vote
favorite
How to check if a dictionary (associative array) is empty? I just declare one using declare -A dict. I want to know if it is just declared but not have any key.
bash shell-script associative-array
edited Dec 7 at 10:14
Kusalananda
120k16225369
asked Dec 7 at 9:56
focus zheng
14
add a comment |
up vote
0
down vote
favorite
up vote
0
down vote
favorite
How to check if a dictionary (associative array) is empty? I just declare one using declare -A dict. I want to know if it is just declared but not have any key.
bash shell-script associative-array
edited Dec 7 at 10:14
Kusalananda
120k16225369
asked Dec 7 at 9:56
focus zheng
14
How to check if a dictionary (associative array) is empty? I just declare one using declare -A dict. I want to know if it is just declared but not have any key.
bash shell-script associative-array
bash shell-script associative-array
edited Dec 7 at 10:14
Kusalananda
120k16225369
asked Dec 7 at 9:56
focus zheng
14
edited Dec 7 at 10:14
Kusalananda
120k16225369
asked Dec 7 at 9:56
focus zheng
14
edited Dec 7 at 10:14
Kusalananda
120k16225369
edited Dec 7 at 10:14
Kusalananda
120k16225369
edited Dec 7 at 10:14
Kusalananda
120k16225369
120k16225369
asked Dec 7 at 9:56
focus zheng
14
asked Dec 7 at 9:56
focus zheng
14
asked Dec 7 at 9:56
focus zheng
14
14
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
up vote
4
down vote
The length of (or the number of elements in) an associative array is available as $#array[@], just like for an ordinary array. If this number is zero, then the array is empty.
if [ "$#array[@]" -ne 0 ]; then
echo 'array is not empty'
fi
On an ordinary shell variable, may use the -v test to test whether it exists or not:
if [ -v variable ]; then
echo 'variable exists'
fi
... but this does not work intuitively on arrays. You can't therefore use this reliably to determine if an array exists but is empty, or whether it hasn't been declared yet.
The test will be true on arrays if their 0 key exists.
answered Dec 7 at 10:01
Kusalananda
120k16225369
Hi @kusa.I find a way to check,if [[ -z $!dict[*] ]];this will check if any key exist.
– focus zheng
Dec 7 at 10:27
@focuszheng This would be better:if [ "$#dict[@]" -ne 0 ]. It's better because the shell does not have to concatenate all the keys together to create a long string.
– Kusalananda
Dec 7 at 10:30
nope, if the dictionary is empty.an error "ubound variable" shows.
– focus zheng
Dec 7 at 10:31
You can test your conditional expression on linux server and bash version >4.4.
– focus zheng
Dec 7 at 10:32
@focuszheng You will get "unbound variable" only if you run underset -u(this is not the default inbash). Also, it is unclear whether you want to check whether an array is empty or whether it is defined.
– Kusalananda
Dec 7 at 10:33
|
show 3 more comments
up vote
-1
down vote
[ -z $!dict[*] ] && echo "yes" || echo "no" yes
this should be fine to check it is empty.
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
answered Dec 7 at 10:44
focus zheng
14
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
The length of (or the number of elements in) an associative array is available as $#array[@], just like for an ordinary array. If this number is zero, then the array is empty.
if [ "$#array[@]" -ne 0 ]; then
echo 'array is not empty'
fi
On an ordinary shell variable, may use the -v test to test whether it exists or not:
if [ -v variable ]; then
echo 'variable exists'
fi
... but this does not work intuitively on arrays. You can't therefore use this reliably to determine if an array exists but is empty, or whether it hasn't been declared yet.
The test will be true on arrays if their 0 key exists.
answered Dec 7 at 10:01
Kusalananda
120k16225369
Hi @kusa.I find a way to check,if [[ -z $!dict[*] ]];this will check if any key exist.
– focus zheng
Dec 7 at 10:27
@focuszheng This would be better:if [ "$#dict[@]" -ne 0 ]. It's better because the shell does not have to concatenate all the keys together to create a long string.
– Kusalananda
Dec 7 at 10:30
nope, if the dictionary is empty.an error "ubound variable" shows.
– focus zheng
Dec 7 at 10:31
You can test your conditional expression on linux server and bash version >4.4.
– focus zheng
Dec 7 at 10:32
@focuszheng You will get "unbound variable" only if you run underset -u(this is not the default inbash). Also, it is unclear whether you want to check whether an array is empty or whether it is defined.
– Kusalananda
Dec 7 at 10:33
|
show 3 more comments
up vote
4
down vote
The length of (or the number of elements in) an associative array is available as $#array[@], just like for an ordinary array. If this number is zero, then the array is empty.
if [ "$#array[@]" -ne 0 ]; then
echo 'array is not empty'
fi
On an ordinary shell variable, may use the -v test to test whether it exists or not:
if [ -v variable ]; then
echo 'variable exists'
fi
... but this does not work intuitively on arrays. You can't therefore use this reliably to determine if an array exists but is empty, or whether it hasn't been declared yet.
The test will be true on arrays if their 0 key exists.
answered Dec 7 at 10:01
Kusalananda
120k16225369
Hi @kusa.I find a way to check,if [[ -z $!dict[*] ]];this will check if any key exist.
– focus zheng
Dec 7 at 10:27
@focuszheng This would be better:if [ "$#dict[@]" -ne 0 ]. It's better because the shell does not have to concatenate all the keys together to create a long string.
– Kusalananda
Dec 7 at 10:30
nope, if the dictionary is empty.an error "ubound variable" shows.
– focus zheng
Dec 7 at 10:31
You can test your conditional expression on linux server and bash version >4.4.
– focus zheng
Dec 7 at 10:32
@focuszheng You will get "unbound variable" only if you run underset -u(this is not the default inbash). Also, it is unclear whether you want to check whether an array is empty or whether it is defined.
– Kusalananda
Dec 7 at 10:33
|
show 3 more comments
up vote
4
down vote
up vote
4
down vote
The length of (or the number of elements in) an associative array is available as $#array[@], just like for an ordinary array. If this number is zero, then the array is empty.
if [ "$#array[@]" -ne 0 ]; then
echo 'array is not empty'
fi
On an ordinary shell variable, may use the -v test to test whether it exists or not:
if [ -v variable ]; then
echo 'variable exists'
fi
... but this does not work intuitively on arrays. You can't therefore use this reliably to determine if an array exists but is empty, or whether it hasn't been declared yet.
The test will be true on arrays if their 0 key exists.
answered Dec 7 at 10:01
Kusalananda
120k16225369
The length of (or the number of elements in) an associative array is available as $#array[@], just like for an ordinary array. If this number is zero, then the array is empty.
if [ "$#array[@]" -ne 0 ]; then
echo 'array is not empty'
fi
On an ordinary shell variable, may use the -v test to test whether it exists or not:
if [ -v variable ]; then
echo 'variable exists'
fi
... but this does not work intuitively on arrays. You can't therefore use this reliably to determine if an array exists but is empty, or whether it hasn't been declared yet.
The test will be true on arrays if their 0 key exists.
answered Dec 7 at 10:01
Kusalananda
120k16225369
edited Dec 7 at 10:31
answered Dec 7 at 10:01
Kusalananda
120k16225369
answered Dec 7 at 10:01
Kusalananda
120k16225369
answered Dec 7 at 10:01
Kusalananda
120k16225369
120k16225369
Hi @kusa.I find a way to check,if [[ -z $!dict[*] ]];this will check if any key exist.
– focus zheng
Dec 7 at 10:27
@focuszheng This would be better:if [ "$#dict[@]" -ne 0 ]. It's better because the shell does not have to concatenate all the keys together to create a long string.
– Kusalananda
Dec 7 at 10:30
nope, if the dictionary is empty.an error "ubound variable" shows.
– focus zheng
Dec 7 at 10:31
You can test your conditional expression on linux server and bash version >4.4.
– focus zheng
Dec 7 at 10:32
@focuszheng You will get "unbound variable" only if you run underset -u(this is not the default inbash). Also, it is unclear whether you want to check whether an array is empty or whether it is defined.
– Kusalananda
Dec 7 at 10:33
|
show 3 more comments
Hi @kusa.I find a way to check,if [[ -z $!dict[*] ]];this will check if any key exist.
– focus zheng
Dec 7 at 10:27
@focuszheng This would be better:if [ "$#dict[@]" -ne 0 ]. It's better because the shell does not have to concatenate all the keys together to create a long string.
– Kusalananda
Dec 7 at 10:30
nope, if the dictionary is empty.an error "ubound variable" shows.
– focus zheng
Dec 7 at 10:31
You can test your conditional expression on linux server and bash version >4.4.
– focus zheng
Dec 7 at 10:32
@focuszheng You will get "unbound variable" only if you run underset -u(this is not the default inbash). Also, it is unclear whether you want to check whether an array is empty or whether it is defined.
– Kusalananda
Dec 7 at 10:33
Hi @kusa.I find a way to check,if [[ -z $!dict[*] ]];this will check if any key exist.
– focus zheng
Dec 7 at 10:27
Hi @kusa.I find a way to check,if [[ -z $!dict[*] ]];this will check if any key exist.
– focus zheng
Dec 7 at 10:27
@focuszheng This would be better:
if [ "$#dict[@]" -ne 0 ]. It's better because the shell does not have to concatenate all the keys together to create a long string.– Kusalananda
Dec 7 at 10:30
@focuszheng This would be better:
if [ "$#dict[@]" -ne 0 ]. It's better because the shell does not have to concatenate all the keys together to create a long string.– Kusalananda
Dec 7 at 10:30
nope, if the dictionary is empty.an error "ubound variable" shows.
– focus zheng
Dec 7 at 10:31
nope, if the dictionary is empty.an error "ubound variable" shows.
– focus zheng
Dec 7 at 10:31
You can test your conditional expression on linux server and bash version >4.4.
– focus zheng
Dec 7 at 10:32
You can test your conditional expression on linux server and bash version >4.4.
– focus zheng
Dec 7 at 10:32
@focuszheng You will get "unbound variable" only if you run under
set -u (this is not the default in bash). Also, it is unclear whether you want to check whether an array is empty or whether it is defined.– Kusalananda
Dec 7 at 10:33
@focuszheng You will get "unbound variable" only if you run under
set -u (this is not the default in bash). Also, it is unclear whether you want to check whether an array is empty or whether it is defined.– Kusalananda
Dec 7 at 10:33
|
show 3 more comments
up vote
-1
down vote
[ -z $!dict[*] ] && echo "yes" || echo "no" yes
this should be fine to check it is empty.
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
answered Dec 7 at 10:44
focus zheng
14
add a comment |
up vote
-1
down vote
[ -z $!dict[*] ] && echo "yes" || echo "no" yes
this should be fine to check it is empty.
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
answered Dec 7 at 10:44
focus zheng
14
add a comment |
up vote
-1
down vote
up vote
-1
down vote
[ -z $!dict[*] ] && echo "yes" || echo "no" yes
this should be fine to check it is empty.
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
answered Dec 7 at 10:44
focus zheng
14
[ -z $!dict[*] ] && echo "yes" || echo "no" yes
this should be fine to check it is empty.
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
answered Dec 7 at 10:44
focus zheng
14
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
edited Dec 7 at 12:40
Jeff Schaller
37.9k1053123
37.9k1053123
answered Dec 7 at 10:44
focus zheng
14
answered Dec 7 at 10:44
focus zheng
14
answered Dec 7 at 10:44
focus zheng
14
14
add a comment |
add a comment |
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