Mixing
What is the difference between `if [[ .. ]] ; then …` and `[[ .. ]] && …`?
What is the difference between the if [[ ... ]] ; then ... and the [[ ... ]] && ... constructs in Bash, other than syntax? For example:
if [[ -d /etc ]] ; then echo "I see." ; else echo "I don't." ; fi
[[ -d /etc ]] && echo "I see." || echo "I don't."
What can one do that the other cannot?
bash
add a comment |
What is the difference between the if [[ ... ]] ; then ... and the [[ ... ]] && ... constructs in Bash, other than syntax? For example:
if [[ -d /etc ]] ; then echo "I see." ; else echo "I don't." ; fi
[[ -d /etc ]] && echo "I see." || echo "I don't."
What can one do that the other cannot?
bash
3
It's BashPitfall #22.
– Benjamin W.
Jan 2 at 14:59
...see also Ternary operator in bash?, especially the comment stackoverflow.com/questions/3953645/… and the answer by Ivan Pozdeev.
– Charles Duffy
Jan 2 at 15:02
add a comment |
What is the difference between the if [[ ... ]] ; then ... and the [[ ... ]] && ... constructs in Bash, other than syntax? For example:
if [[ -d /etc ]] ; then echo "I see." ; else echo "I don't." ; fi
[[ -d /etc ]] && echo "I see." || echo "I don't."
What can one do that the other cannot?
bash
What is the difference between the if [[ ... ]] ; then ... and the [[ ... ]] && ... constructs in Bash, other than syntax? For example:
if [[ -d /etc ]] ; then echo "I see." ; else echo "I don't." ; fi
[[ -d /etc ]] && echo "I see." || echo "I don't."
What can one do that the other cannot?
bash
bash
asked Jan 2 at 14:26
user8370684
3
It's BashPitfall #22.
– Benjamin W.
Jan 2 at 14:59
...see also Ternary operator in bash?, especially the comment stackoverflow.com/questions/3953645/… and the answer by Ivan Pozdeev.
– Charles Duffy
Jan 2 at 15:02
add a comment |
3
It's BashPitfall #22.
– Benjamin W.
Jan 2 at 14:59
...see also Ternary operator in bash?, especially the comment stackoverflow.com/questions/3953645/… and the answer by Ivan Pozdeev.
– Charles Duffy
Jan 2 at 15:02
3
3
It's BashPitfall #22.
– Benjamin W.
Jan 2 at 14:59
It's BashPitfall #22.
– Benjamin W.
Jan 2 at 14:59
...see also Ternary operator in bash?, especially the comment stackoverflow.com/questions/3953645/… and the answer by Ivan Pozdeev.
– Charles Duffy
Jan 2 at 15:02
...see also Ternary operator in bash?, especially the comment stackoverflow.com/questions/3953645/… and the answer by Ivan Pozdeev.
– Charles Duffy
Jan 2 at 15:02
add a comment |
2 Answers
2
active
oldest
votes
There are not many differences, but one is that the first example is only using the first condition. In the second there are two conditions that effect the output.
if [[ -d /etc ]] ; # only condition that matters
then echo "I see." ;
else echo "I don't." ;
fi
[[ -d /etc ]] && # condition 1
echo "I see." || # condition 2
echo "I don't."
In this example condtion 2 will always be fine, as echo is a builtin function, but if it was another command, and it failed it would trigger the or clause, which is not possible in the first example. The first one only uses one condition the second relies on two conditions.
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
2
Technically,echocan fail (for instance, if its standard output is redirected to a read-only file); it's just isn't common.
– chepner
Jan 2 at 14:38
add a comment |
Addendum - It is a relevant aside that you can put multiple statements in each block of a properly formatted if/then/elif/else without much special effort (though it does take some finagling on the if part) but the ternary construct requires that you create blocks yourself.
if true && false || oops
then : "this shan't be executed"
: but I can put several statements anyway
elif true && true || oops
then echo hello
echo more statements!
else : I could put more statements here too
: see?
fi
bash: oops: command not found
hello
more statements!
To create multiple-statements blocks in a ternary you need something like this -
true && {
echo ok
echo more
oops!
} || false {
echo This still has the same logical vulnerability, now made *worse*
echo oh, woe.
}
ok
more
bash: oops!: command not found
echo This still has the same logical vulnerability
This still has the same logical vulnerability
echo oh, woe.
oh, woe.
}
bash: syntax error near unexpected token `}'
It could be cleaned up a bit, but that isn't the point.
They aren't the same.
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54008074%2fwhat-is-the-difference-between-if-then-and%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
There are not many differences, but one is that the first example is only using the first condition. In the second there are two conditions that effect the output.
if [[ -d /etc ]] ; # only condition that matters
then echo "I see." ;
else echo "I don't." ;
fi
[[ -d /etc ]] && # condition 1
echo "I see." || # condition 2
echo "I don't."
In this example condtion 2 will always be fine, as echo is a builtin function, but if it was another command, and it failed it would trigger the or clause, which is not possible in the first example. The first one only uses one condition the second relies on two conditions.
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
2
Technically,echocan fail (for instance, if its standard output is redirected to a read-only file); it's just isn't common.
– chepner
Jan 2 at 14:38
add a comment |
There are not many differences, but one is that the first example is only using the first condition. In the second there are two conditions that effect the output.
if [[ -d /etc ]] ; # only condition that matters
then echo "I see." ;
else echo "I don't." ;
fi
[[ -d /etc ]] && # condition 1
echo "I see." || # condition 2
echo "I don't."
In this example condtion 2 will always be fine, as echo is a builtin function, but if it was another command, and it failed it would trigger the or clause, which is not possible in the first example. The first one only uses one condition the second relies on two conditions.
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
2
Technically,echocan fail (for instance, if its standard output is redirected to a read-only file); it's just isn't common.
– chepner
Jan 2 at 14:38
add a comment |
There are not many differences, but one is that the first example is only using the first condition. In the second there are two conditions that effect the output.
if [[ -d /etc ]] ; # only condition that matters
then echo "I see." ;
else echo "I don't." ;
fi
[[ -d /etc ]] && # condition 1
echo "I see." || # condition 2
echo "I don't."
In this example condtion 2 will always be fine, as echo is a builtin function, but if it was another command, and it failed it would trigger the or clause, which is not possible in the first example. The first one only uses one condition the second relies on two conditions.
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
There are not many differences, but one is that the first example is only using the first condition. In the second there are two conditions that effect the output.
if [[ -d /etc ]] ; # only condition that matters
then echo "I see." ;
else echo "I don't." ;
fi
[[ -d /etc ]] && # condition 1
echo "I see." || # condition 2
echo "I don't."
In this example condtion 2 will always be fine, as echo is a builtin function, but if it was another command, and it failed it would trigger the or clause, which is not possible in the first example. The first one only uses one condition the second relies on two conditions.
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
answered Jan 2 at 14:35
Nick EllisNick Ellis
752818
752818
2
Technically,echocan fail (for instance, if its standard output is redirected to a read-only file); it's just isn't common.
– chepner
Jan 2 at 14:38
add a comment |
2
Technically,echocan fail (for instance, if its standard output is redirected to a read-only file); it's just isn't common.
– chepner
Jan 2 at 14:38
2
2
Technically,
echo can fail (for instance, if its standard output is redirected to a read-only file); it's just isn't common.– chepner
Jan 2 at 14:38
Technically,
echo can fail (for instance, if its standard output is redirected to a read-only file); it's just isn't common.– chepner
Jan 2 at 14:38
add a comment |
Addendum - It is a relevant aside that you can put multiple statements in each block of a properly formatted if/then/elif/else without much special effort (though it does take some finagling on the if part) but the ternary construct requires that you create blocks yourself.
if true && false || oops
then : "this shan't be executed"
: but I can put several statements anyway
elif true && true || oops
then echo hello
echo more statements!
else : I could put more statements here too
: see?
fi
bash: oops: command not found
hello
more statements!
To create multiple-statements blocks in a ternary you need something like this -
true && {
echo ok
echo more
oops!
} || false {
echo This still has the same logical vulnerability, now made *worse*
echo oh, woe.
}
ok
more
bash: oops!: command not found
echo This still has the same logical vulnerability
This still has the same logical vulnerability
echo oh, woe.
oh, woe.
}
bash: syntax error near unexpected token `}'
It could be cleaned up a bit, but that isn't the point.
They aren't the same.
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
add a comment |
Addendum - It is a relevant aside that you can put multiple statements in each block of a properly formatted if/then/elif/else without much special effort (though it does take some finagling on the if part) but the ternary construct requires that you create blocks yourself.
if true && false || oops
then : "this shan't be executed"
: but I can put several statements anyway
elif true && true || oops
then echo hello
echo more statements!
else : I could put more statements here too
: see?
fi
bash: oops: command not found
hello
more statements!
To create multiple-statements blocks in a ternary you need something like this -
true && {
echo ok
echo more
oops!
} || false {
echo This still has the same logical vulnerability, now made *worse*
echo oh, woe.
}
ok
more
bash: oops!: command not found
echo This still has the same logical vulnerability
This still has the same logical vulnerability
echo oh, woe.
oh, woe.
}
bash: syntax error near unexpected token `}'
It could be cleaned up a bit, but that isn't the point.
They aren't the same.
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
add a comment |
Addendum - It is a relevant aside that you can put multiple statements in each block of a properly formatted if/then/elif/else without much special effort (though it does take some finagling on the if part) but the ternary construct requires that you create blocks yourself.
if true && false || oops
then : "this shan't be executed"
: but I can put several statements anyway
elif true && true || oops
then echo hello
echo more statements!
else : I could put more statements here too
: see?
fi
bash: oops: command not found
hello
more statements!
To create multiple-statements blocks in a ternary you need something like this -
true && {
echo ok
echo more
oops!
} || false {
echo This still has the same logical vulnerability, now made *worse*
echo oh, woe.
}
ok
more
bash: oops!: command not found
echo This still has the same logical vulnerability
This still has the same logical vulnerability
echo oh, woe.
oh, woe.
}
bash: syntax error near unexpected token `}'
It could be cleaned up a bit, but that isn't the point.
They aren't the same.
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
Addendum - It is a relevant aside that you can put multiple statements in each block of a properly formatted if/then/elif/else without much special effort (though it does take some finagling on the if part) but the ternary construct requires that you create blocks yourself.
if true && false || oops
then : "this shan't be executed"
: but I can put several statements anyway
elif true && true || oops
then echo hello
echo more statements!
else : I could put more statements here too
: see?
fi
bash: oops: command not found
hello
more statements!
To create multiple-statements blocks in a ternary you need something like this -
true && {
echo ok
echo more
oops!
} || false {
echo This still has the same logical vulnerability, now made *worse*
echo oh, woe.
}
ok
more
bash: oops!: command not found
echo This still has the same logical vulnerability
This still has the same logical vulnerability
echo oh, woe.
oh, woe.
}
bash: syntax error near unexpected token `}'
It could be cleaned up a bit, but that isn't the point.
They aren't the same.
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
answered Jan 2 at 15:27
Paul HodgesPaul Hodges
3,7601524
3,7601524
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54008074%2fwhat-is-the-difference-between-if-then-and%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
3
It's BashPitfall #22.
– Benjamin W.
Jan 2 at 14:59
...see also Ternary operator in bash?, especially the comment stackoverflow.com/questions/3953645/… and the answer by Ivan Pozdeev.
– Charles Duffy
Jan 2 at 15:02