Difference between [ and [[ in if statements [duplicate]

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This question already has an answer here:

What is the difference between [[ $a == z* ]] and [ $a == z* ]?

3 answers

Why does parameter expansion with spaces without quotes work inside double brackets â€œ[[â€ but not inside single brackets â€œ[â€?

4 answers

The following code

if [ $a == "apple" ];
then
 echo "True"
else
 echo "False"
fi

outputs "True" ("False") if a="apple" (a="plum"). The comparison fails if one uses wildcards:

if [ $a == "appl"* ];

and is fixed if one replaces [ by [[:

if [[ $a == "appl"* ]];

What is the difference between [ and [[ in if statements?

asked Dec 23 '17 at 15:52

Viesturs

224138

marked as duplicate by don_crissti, ilkkachu, Communityâ™¦ Dec 23 '17 at 16:11

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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up vote
0
down vote

favorite

This question already has an answer here:

What is the difference between [[ $a == z* ]] and [ $a == z* ]?

3 answers

Why does parameter expansion with spaces without quotes work inside double brackets â€œ[[â€ but not inside single brackets â€œ[â€?

4 answers

The following code

if [ $a == "apple" ];
then
 echo "True"
else
 echo "False"
fi

outputs "True" ("False") if a="apple" (a="plum"). The comparison fails if one uses wildcards:

if [ $a == "appl"* ];

and is fixed if one replaces [ by [[:

if [[ $a == "appl"* ]];

What is the difference between [ and [[ in if statements?

asked Dec 23 '17 at 15:52

Viesturs

224138

marked as duplicate by don_crissti, ilkkachu, Communityâ™¦ Dec 23 '17 at 16:11

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

add a commentÂ |Â

up vote
0
down vote

favorite

This question already has an answer here:

What is the difference between [[ $a == z* ]] and [ $a == z* ]?

3 answers

Why does parameter expansion with spaces without quotes work inside double brackets â€œ[[â€ but not inside single brackets â€œ[â€?

4 answers

The following code

if [ $a == "apple" ];
then
 echo "True"
else
 echo "False"
fi

outputs "True" ("False") if a="apple" (a="plum"). The comparison fails if one uses wildcards:

if [ $a == "appl"* ];

and is fixed if one replaces [ by [[:

if [[ $a == "appl"* ]];

What is the difference between [ and [[ in if statements?

asked Dec 23 '17 at 15:52

Viesturs

224138

This question already has an answer here:

What is the difference between [[ $a == z* ]] and [ $a == z* ]?

3 answers

Why does parameter expansion with spaces without quotes work inside double brackets â€œ[[â€ but not inside single brackets â€œ[â€?

4 answers

The following code

if [ $a == "apple" ];
then
 echo "True"
else
 echo "False"
fi

outputs "True" ("False") if a="apple" (a="plum"). The comparison fails if one uses wildcards:

if [ $a == "appl"* ];

and is fixed if one replaces [ by [[:

if [[ $a == "appl"* ]];

What is the difference between [ and [[ in if statements?

This question already has an answer here:

What is the difference between [[ $a == z* ]] and [ $a == z* ]?

3 answers

Why does parameter expansion with spaces without quotes work inside double brackets â€œ[[â€ but not inside single brackets â€œ[â€?

4 answers

asked Dec 23 '17 at 15:52

Viesturs

224138

asked Dec 23 '17 at 15:52

Viesturs

224138

asked Dec 23 '17 at 15:52

Viesturs

224138

asked Dec 23 '17 at 15:52

Viesturs

224138

marked as duplicate by don_crissti, ilkkachu, Communityâ™¦ Dec 23 '17 at 16:11

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

marked as duplicate by don_crissti, ilkkachu, Communityâ™¦ Dec 23 '17 at 16:11

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

add a commentÂ |Â

1 Answer
1

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oldest

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up vote
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[ is a command (basically a variant of the test command). [[ is a builtin in many shells.

When you write foo* inside [...] filename expansion (aka globbing) occurs; while inside [[...]] pattern matching occurs.

[[ is more powerful and capable than [ but should not be used if portability is a concern.

[ and [[ are not part of the if syntax, you can use them as in [ "$exit" = 'yes' ] && exit.

Inside [...] you should prefer = instead of ==. As far as I know, the second one is accepted in many shells but is not POSIX-compliant.

By the way, I recommend you to double-quote your variables even if you really know how word splitting will behave.

edited Dec 23 '17 at 16:28

answered Dec 23 '17 at 16:10

nxnev

2,4622423

add a commentÂ |Â

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

up vote
2
down vote

accepted

[ is a command (basically a variant of the test command). [[ is a builtin in many shells.

When you write foo* inside [...] filename expansion (aka globbing) occurs; while inside [[...]] pattern matching occurs.

[[ is more powerful and capable than [ but should not be used if portability is a concern.

[ and [[ are not part of the if syntax, you can use them as in [ "$exit" = 'yes' ] && exit.

Inside [...] you should prefer = instead of ==. As far as I know, the second one is accepted in many shells but is not POSIX-compliant.

By the way, I recommend you to double-quote your variables even if you really know how word splitting will behave.

edited Dec 23 '17 at 16:28

answered Dec 23 '17 at 16:10

nxnev

2,4622423

add a commentÂ |Â

up vote
2
down vote

accepted

[ is a command (basically a variant of the test command). [[ is a builtin in many shells.

When you write foo* inside [...] filename expansion (aka globbing) occurs; while inside [[...]] pattern matching occurs.

[[ is more powerful and capable than [ but should not be used if portability is a concern.

[ and [[ are not part of the if syntax, you can use them as in [ "$exit" = 'yes' ] && exit.

Inside [...] you should prefer = instead of ==. As far as I know, the second one is accepted in many shells but is not POSIX-compliant.

By the way, I recommend you to double-quote your variables even if you really know how word splitting will behave.

edited Dec 23 '17 at 16:28

answered Dec 23 '17 at 16:10

nxnev

2,4622423

add a commentÂ |Â

up vote
2
down vote

accepted

[ is a command (basically a variant of the test command). [[ is a builtin in many shells.

When you write foo* inside [...] filename expansion (aka globbing) occurs; while inside [[...]] pattern matching occurs.

[[ is more powerful and capable than [ but should not be used if portability is a concern.

[ and [[ are not part of the if syntax, you can use them as in [ "$exit" = 'yes' ] && exit.

Inside [...] you should prefer = instead of ==. As far as I know, the second one is accepted in many shells but is not POSIX-compliant.

By the way, I recommend you to double-quote your variables even if you really know how word splitting will behave.

edited Dec 23 '17 at 16:28

answered Dec 23 '17 at 16:10

nxnev

2,4622423

[ is a command (basically a variant of the test command). [[ is a builtin in many shells.

When you write foo* inside [...] filename expansion (aka globbing) occurs; while inside [[...]] pattern matching occurs.

[[ is more powerful and capable than [ but should not be used if portability is a concern.

[ and [[ are not part of the if syntax, you can use them as in [ "$exit" = 'yes' ] && exit.

Inside [...] you should prefer = instead of ==. As far as I know, the second one is accepted in many shells but is not POSIX-compliant.

By the way, I recommend you to double-quote your variables even if you really know how word splitting will behave.

edited Dec 23 '17 at 16:28

answered Dec 23 '17 at 16:10

nxnev

2,4622423

edited Dec 23 '17 at 16:28

answered Dec 23 '17 at 16:10

nxnev

2,4622423

answered Dec 23 '17 at 16:10

nxnev

2,4622423

answered Dec 23 '17 at 16:10

nxnev

2,4622423

add a commentÂ |Â

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