What's the purpose of “true” in bash “if sudo true; then” Unicorn Meta Zoo #1: Why another podcast? Announcing the arrival of Valued Associate #679: Cesar Manara 2019 Community Moderator Election Results Why I closed the “Why is Kali so hard” questionHow can I adjust this short shell script to fit my needs?Security of sudo not asking for a password after the first timeCan't give myself NOPASSWD privelege for chmod/chownHow to prevent the caller's shell from being used in sudoScript that asks for four words, then tells the user the word they chose. Output error?Sudo specific command with no passwordHave a command in my $PATH, but it is not being recognized when I use sudoHow to check a set of lines in a text file for patterns using awk, sed, or grep?Which user's password does `sudo` asks for?Does sudo restrict on which users can acquire superuser privileges?
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What's the purpose of “true” in bash “if sudo true; then”
Unicorn Meta Zoo #1: Why another podcast?
Announcing the arrival of Valued Associate #679: Cesar Manara
2019 Community Moderator Election Results
Why I closed the “Why is Kali so hard” questionHow can I adjust this short shell script to fit my needs?Security of sudo not asking for a password after the first timeCan't give myself NOPASSWD privelege for chmod/chownHow to prevent the caller's shell from being used in sudoScript that asks for four words, then tells the user the word they chose. Output error?Sudo specific command with no passwordHave a command in my $PATH, but it is not being recognized when I use sudoHow to check a set of lines in a text file for patterns using awk, sed, or grep?Which user's password does `sudo` asks for?Does sudo restrict on which users can acquire superuser privileges?
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I've hacked together this bash script which tests if the user has superuser privileges and if they don't it asks for them. Ultimately I'm trying to invert the second 'if' statement so that I can remove the following two lines (the echo "password ok" and the else on the following line)
# Root user only
if [[ "$EUID" != 0 ]]; then
sudo -k # make sure to ask for password on next sudo
if sudo true; then
echo "Password ok"
else
echo "Aborting script"
exit 1
fi
fi
echo "do my ops"
Is the purpose of "true" on the fourth line just a null-statement?
I need to invert the test on the fourth line, how do I do so? Here is what I've tried:
if sudo false; then
if sudo true == false; then
if [!(sudo true)]; then
bash sudo
|
show 7 more comments
I've hacked together this bash script which tests if the user has superuser privileges and if they don't it asks for them. Ultimately I'm trying to invert the second 'if' statement so that I can remove the following two lines (the echo "password ok" and the else on the following line)
# Root user only
if [[ "$EUID" != 0 ]]; then
sudo -k # make sure to ask for password on next sudo
if sudo true; then
echo "Password ok"
else
echo "Aborting script"
exit 1
fi
fi
echo "do my ops"
Is the purpose of "true" on the fourth line just a null-statement?
I need to invert the test on the fourth line, how do I do so? Here is what I've tried:
if sudo false; then
if sudo true == false; then
if [!(sudo true)]; then
bash sudo
2
If you're going to downvote the question, please could you explain what I can do to improve the question? Is this not the right overflow site?
– Matt Parkins
Mar 26 at 14:47
4
Not sure where the downvotes are coming from; are you trying to negate the statement or nullify the statement? You say you want to get rid of both the true/echo and the "else", so what's your final objective?
– Jeff Schaller♦
Mar 26 at 14:52
1
see stackoverflow.com/q/10552711/537980
– ctrl-alt-delor
Mar 26 at 14:55
1
@ctrl-alt-delor following that link it seems all I need do is put an exclamation mark in front of the sudo and then I can remove both the echo and the else, and now i've tested it, that works, thanks.
– Matt Parkins
Mar 26 at 15:15
2
In passing, you probably ought to redirect the error message to the error stream:echo "Aborting script" >&2
– Toby Speight
Mar 26 at 17:24
|
show 7 more comments
I've hacked together this bash script which tests if the user has superuser privileges and if they don't it asks for them. Ultimately I'm trying to invert the second 'if' statement so that I can remove the following two lines (the echo "password ok" and the else on the following line)
# Root user only
if [[ "$EUID" != 0 ]]; then
sudo -k # make sure to ask for password on next sudo
if sudo true; then
echo "Password ok"
else
echo "Aborting script"
exit 1
fi
fi
echo "do my ops"
Is the purpose of "true" on the fourth line just a null-statement?
I need to invert the test on the fourth line, how do I do so? Here is what I've tried:
if sudo false; then
if sudo true == false; then
if [!(sudo true)]; then
bash sudo
I've hacked together this bash script which tests if the user has superuser privileges and if they don't it asks for them. Ultimately I'm trying to invert the second 'if' statement so that I can remove the following two lines (the echo "password ok" and the else on the following line)
# Root user only
if [[ "$EUID" != 0 ]]; then
sudo -k # make sure to ask for password on next sudo
if sudo true; then
echo "Password ok"
else
echo "Aborting script"
exit 1
fi
fi
echo "do my ops"
Is the purpose of "true" on the fourth line just a null-statement?
I need to invert the test on the fourth line, how do I do so? Here is what I've tried:
if sudo false; then
if sudo true == false; then
if [!(sudo true)]; then
bash sudo
bash sudo
edited Mar 27 at 12:00
Matt Parkins
asked Mar 26 at 14:43
Matt ParkinsMatt Parkins
20727
20727
2
If you're going to downvote the question, please could you explain what I can do to improve the question? Is this not the right overflow site?
– Matt Parkins
Mar 26 at 14:47
4
Not sure where the downvotes are coming from; are you trying to negate the statement or nullify the statement? You say you want to get rid of both the true/echo and the "else", so what's your final objective?
– Jeff Schaller♦
Mar 26 at 14:52
1
see stackoverflow.com/q/10552711/537980
– ctrl-alt-delor
Mar 26 at 14:55
1
@ctrl-alt-delor following that link it seems all I need do is put an exclamation mark in front of the sudo and then I can remove both the echo and the else, and now i've tested it, that works, thanks.
– Matt Parkins
Mar 26 at 15:15
2
In passing, you probably ought to redirect the error message to the error stream:echo "Aborting script" >&2
– Toby Speight
Mar 26 at 17:24
|
show 7 more comments
2
If you're going to downvote the question, please could you explain what I can do to improve the question? Is this not the right overflow site?
– Matt Parkins
Mar 26 at 14:47
4
Not sure where the downvotes are coming from; are you trying to negate the statement or nullify the statement? You say you want to get rid of both the true/echo and the "else", so what's your final objective?
– Jeff Schaller♦
Mar 26 at 14:52
1
see stackoverflow.com/q/10552711/537980
– ctrl-alt-delor
Mar 26 at 14:55
1
@ctrl-alt-delor following that link it seems all I need do is put an exclamation mark in front of the sudo and then I can remove both the echo and the else, and now i've tested it, that works, thanks.
– Matt Parkins
Mar 26 at 15:15
2
In passing, you probably ought to redirect the error message to the error stream:echo "Aborting script" >&2
– Toby Speight
Mar 26 at 17:24
2
2
If you're going to downvote the question, please could you explain what I can do to improve the question? Is this not the right overflow site?
– Matt Parkins
Mar 26 at 14:47
If you're going to downvote the question, please could you explain what I can do to improve the question? Is this not the right overflow site?
– Matt Parkins
Mar 26 at 14:47
4
4
Not sure where the downvotes are coming from; are you trying to negate the statement or nullify the statement? You say you want to get rid of both the true/echo and the "else", so what's your final objective?
– Jeff Schaller♦
Mar 26 at 14:52
Not sure where the downvotes are coming from; are you trying to negate the statement or nullify the statement? You say you want to get rid of both the true/echo and the "else", so what's your final objective?
– Jeff Schaller♦
Mar 26 at 14:52
1
1
see stackoverflow.com/q/10552711/537980
– ctrl-alt-delor
Mar 26 at 14:55
see stackoverflow.com/q/10552711/537980
– ctrl-alt-delor
Mar 26 at 14:55
1
1
@ctrl-alt-delor following that link it seems all I need do is put an exclamation mark in front of the sudo and then I can remove both the echo and the else, and now i've tested it, that works, thanks.
– Matt Parkins
Mar 26 at 15:15
@ctrl-alt-delor following that link it seems all I need do is put an exclamation mark in front of the sudo and then I can remove both the echo and the else, and now i've tested it, that works, thanks.
– Matt Parkins
Mar 26 at 15:15
2
2
In passing, you probably ought to redirect the error message to the error stream:
echo "Aborting script" >&2
– Toby Speight
Mar 26 at 17:24
In passing, you probably ought to redirect the error message to the error stream:
echo "Aborting script" >&2
– Toby Speight
Mar 26 at 17:24
|
show 7 more comments
3 Answers
3
active
oldest
votes
true
in bash isn't a keyword, it's a program that instantly exits with a successful exit code.
Likewise, false
is a program that exits with an unsuccessful exit code.
You can try this out by running both programs from your terminal, and then reading the $?
variable, which contains the exit code of the last program;
true
echo $? # 0
false
echo $? #1
if sudo true
isn't equivalent to if sudo == true
. if sudo true
is running the true
program using sudo
, and checking the exit code.
Therefore:
if sudo false; then
is running the program false
as sudo. The return will always be false.
if sudo true == false
will run the program true
with the arguments ==
and false
using sudo
. This obviously isn't want you intended.
if [!(sudo true)]
is invalid syntax.
What you are probably looking for is
if ! sudo true;
12
As a slightly pedantic correction to the first sentence: in bash,true
andfalse
are "builtins", commands interpreted directly by the shell; in Unix-like systems in general, they also exist as standalone programs on the file system. The difference doesn't matter that much here, but as far as I know,sudo true
will be running the standalone program, not the bash builtin.
– IMSoP
Mar 26 at 19:11
31
PS: my favourite summaries oftrue
andfalse
are the titles on their man pages:true - do nothing, successfully
andfalse - do nothing, unsuccessfully
– IMSoP
Mar 26 at 19:14
3
@IMSoP That's deep.
– brainplot
Mar 27 at 12:54
2
Iftrue
didn't exist, the code in the question shows why one might need to invent it! It's a minimal program that can only fail if the system it's on is truly borked. So one can use it to establish if one's access credentials are OK.
– nigel222
Mar 27 at 17:22
2
In AT&T SYSV Unix, "true" was a shell script /bin/true, which consisted of a large copyright notice in comments...and nothing else.
– Lee Daniel Crocker
Mar 27 at 20:15
|
show 4 more comments
I feel like the accepted answer didn't actually answer your question?
The purpose of doing this is to check that you can actually sudo
.
How this check is performed is via the true
program as explained in the accepted answer.
1
Essentially, this. Alternative could be to check if the user is in sudoers group, but just runningsudo true
is also easy enough of a way, although a bit hacky.
– Sergiy Kolodyazhnyy
Mar 27 at 3:32
3
Note that this also requiressudo
to be installed, so the checks wouldn't be entirely equivalent... you could be in the sudoers group and still not be able to sudo. (This can especially come up if you're e.g. writing a script to setup a new image from a minimal rootfs tarball, which might not have sudo.)
– Mehrdad
Mar 27 at 3:38
1
The OP wants to drop out if you cannot sudo, and get rid of two lines rather than have an else following a noop.
– mckenzm
Mar 27 at 4:10
2
And, conversely, you can also be able tosudo
without being in the sudoers group if you (either personally or as a member of some other group) are listed in/etc/sudoers
. But evensudo true
is not infallible, assudo
access can be granted for only specific commands, so you may be able tosudo true
, but not tosudo something_else
, or vice-versa. There's no iron-clad way to test other than by trying to run the command you actually want to run withsudo
.
– Dave Sherohman
Mar 27 at 14:42
2
Also, you can be in thesudoers
group and not be able tosudo
because thesudoers
group is not listed in thesudoers
file. A group with the four letterssudo
in its name is not a valid indication of whether or not a user in that group can do any particular thing or anything at all usingsudo
.
– jrw32982
Mar 27 at 19:13
|
show 1 more comment
As I see in this script. It is just checking if sudo is enabled, that is it..
true just returns true.
So in this case if they need to run any command with sudo it checks at start first, asking the password only one time.
The condition works like this: if sudo are executing the true command correctly, it will return true for the if condition, then sudo is enabled and the user typed the password correctly, else you typed the password wrong or sudo is not enabled, the script must not continue.
The other commands do not need to ask sudo password, because your authentication are sucessfully in first time (but this depends on the sudo configuration, so this scripts depends much in the environment configuration)
The 'echo password ok' demonstrate that too. the shell script will not ask the password anymore.
1
The only commands that run through sudo there aresudo true
andsudo -k
. The latter explicitly doesn't require a password. None of the other commands in the script run via sudo, so of course they will not require passwords, regardless of if the authentication was successful the first time.
– ilkkachu
Mar 26 at 15:10
I wrote: "So in this case if they need to run any command with sudo it checks at start first, asking the password only one time. "
– Luciano Andress Martini
Mar 26 at 15:29
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
true
in bash isn't a keyword, it's a program that instantly exits with a successful exit code.
Likewise, false
is a program that exits with an unsuccessful exit code.
You can try this out by running both programs from your terminal, and then reading the $?
variable, which contains the exit code of the last program;
true
echo $? # 0
false
echo $? #1
if sudo true
isn't equivalent to if sudo == true
. if sudo true
is running the true
program using sudo
, and checking the exit code.
Therefore:
if sudo false; then
is running the program false
as sudo. The return will always be false.
if sudo true == false
will run the program true
with the arguments ==
and false
using sudo
. This obviously isn't want you intended.
if [!(sudo true)]
is invalid syntax.
What you are probably looking for is
if ! sudo true;
12
As a slightly pedantic correction to the first sentence: in bash,true
andfalse
are "builtins", commands interpreted directly by the shell; in Unix-like systems in general, they also exist as standalone programs on the file system. The difference doesn't matter that much here, but as far as I know,sudo true
will be running the standalone program, not the bash builtin.
– IMSoP
Mar 26 at 19:11
31
PS: my favourite summaries oftrue
andfalse
are the titles on their man pages:true - do nothing, successfully
andfalse - do nothing, unsuccessfully
– IMSoP
Mar 26 at 19:14
3
@IMSoP That's deep.
– brainplot
Mar 27 at 12:54
2
Iftrue
didn't exist, the code in the question shows why one might need to invent it! It's a minimal program that can only fail if the system it's on is truly borked. So one can use it to establish if one's access credentials are OK.
– nigel222
Mar 27 at 17:22
2
In AT&T SYSV Unix, "true" was a shell script /bin/true, which consisted of a large copyright notice in comments...and nothing else.
– Lee Daniel Crocker
Mar 27 at 20:15
|
show 4 more comments
true
in bash isn't a keyword, it's a program that instantly exits with a successful exit code.
Likewise, false
is a program that exits with an unsuccessful exit code.
You can try this out by running both programs from your terminal, and then reading the $?
variable, which contains the exit code of the last program;
true
echo $? # 0
false
echo $? #1
if sudo true
isn't equivalent to if sudo == true
. if sudo true
is running the true
program using sudo
, and checking the exit code.
Therefore:
if sudo false; then
is running the program false
as sudo. The return will always be false.
if sudo true == false
will run the program true
with the arguments ==
and false
using sudo
. This obviously isn't want you intended.
if [!(sudo true)]
is invalid syntax.
What you are probably looking for is
if ! sudo true;
12
As a slightly pedantic correction to the first sentence: in bash,true
andfalse
are "builtins", commands interpreted directly by the shell; in Unix-like systems in general, they also exist as standalone programs on the file system. The difference doesn't matter that much here, but as far as I know,sudo true
will be running the standalone program, not the bash builtin.
– IMSoP
Mar 26 at 19:11
31
PS: my favourite summaries oftrue
andfalse
are the titles on their man pages:true - do nothing, successfully
andfalse - do nothing, unsuccessfully
– IMSoP
Mar 26 at 19:14
3
@IMSoP That's deep.
– brainplot
Mar 27 at 12:54
2
Iftrue
didn't exist, the code in the question shows why one might need to invent it! It's a minimal program that can only fail if the system it's on is truly borked. So one can use it to establish if one's access credentials are OK.
– nigel222
Mar 27 at 17:22
2
In AT&T SYSV Unix, "true" was a shell script /bin/true, which consisted of a large copyright notice in comments...and nothing else.
– Lee Daniel Crocker
Mar 27 at 20:15
|
show 4 more comments
true
in bash isn't a keyword, it's a program that instantly exits with a successful exit code.
Likewise, false
is a program that exits with an unsuccessful exit code.
You can try this out by running both programs from your terminal, and then reading the $?
variable, which contains the exit code of the last program;
true
echo $? # 0
false
echo $? #1
if sudo true
isn't equivalent to if sudo == true
. if sudo true
is running the true
program using sudo
, and checking the exit code.
Therefore:
if sudo false; then
is running the program false
as sudo. The return will always be false.
if sudo true == false
will run the program true
with the arguments ==
and false
using sudo
. This obviously isn't want you intended.
if [!(sudo true)]
is invalid syntax.
What you are probably looking for is
if ! sudo true;
true
in bash isn't a keyword, it's a program that instantly exits with a successful exit code.
Likewise, false
is a program that exits with an unsuccessful exit code.
You can try this out by running both programs from your terminal, and then reading the $?
variable, which contains the exit code of the last program;
true
echo $? # 0
false
echo $? #1
if sudo true
isn't equivalent to if sudo == true
. if sudo true
is running the true
program using sudo
, and checking the exit code.
Therefore:
if sudo false; then
is running the program false
as sudo. The return will always be false.
if sudo true == false
will run the program true
with the arguments ==
and false
using sudo
. This obviously isn't want you intended.
if [!(sudo true)]
is invalid syntax.
What you are probably looking for is
if ! sudo true;
answered Mar 26 at 14:58
JShorthouseJShorthouse
54829
54829
12
As a slightly pedantic correction to the first sentence: in bash,true
andfalse
are "builtins", commands interpreted directly by the shell; in Unix-like systems in general, they also exist as standalone programs on the file system. The difference doesn't matter that much here, but as far as I know,sudo true
will be running the standalone program, not the bash builtin.
– IMSoP
Mar 26 at 19:11
31
PS: my favourite summaries oftrue
andfalse
are the titles on their man pages:true - do nothing, successfully
andfalse - do nothing, unsuccessfully
– IMSoP
Mar 26 at 19:14
3
@IMSoP That's deep.
– brainplot
Mar 27 at 12:54
2
Iftrue
didn't exist, the code in the question shows why one might need to invent it! It's a minimal program that can only fail if the system it's on is truly borked. So one can use it to establish if one's access credentials are OK.
– nigel222
Mar 27 at 17:22
2
In AT&T SYSV Unix, "true" was a shell script /bin/true, which consisted of a large copyright notice in comments...and nothing else.
– Lee Daniel Crocker
Mar 27 at 20:15
|
show 4 more comments
12
As a slightly pedantic correction to the first sentence: in bash,true
andfalse
are "builtins", commands interpreted directly by the shell; in Unix-like systems in general, they also exist as standalone programs on the file system. The difference doesn't matter that much here, but as far as I know,sudo true
will be running the standalone program, not the bash builtin.
– IMSoP
Mar 26 at 19:11
31
PS: my favourite summaries oftrue
andfalse
are the titles on their man pages:true - do nothing, successfully
andfalse - do nothing, unsuccessfully
– IMSoP
Mar 26 at 19:14
3
@IMSoP That's deep.
– brainplot
Mar 27 at 12:54
2
Iftrue
didn't exist, the code in the question shows why one might need to invent it! It's a minimal program that can only fail if the system it's on is truly borked. So one can use it to establish if one's access credentials are OK.
– nigel222
Mar 27 at 17:22
2
In AT&T SYSV Unix, "true" was a shell script /bin/true, which consisted of a large copyright notice in comments...and nothing else.
– Lee Daniel Crocker
Mar 27 at 20:15
12
12
As a slightly pedantic correction to the first sentence: in bash,
true
and false
are "builtins", commands interpreted directly by the shell; in Unix-like systems in general, they also exist as standalone programs on the file system. The difference doesn't matter that much here, but as far as I know, sudo true
will be running the standalone program, not the bash builtin.– IMSoP
Mar 26 at 19:11
As a slightly pedantic correction to the first sentence: in bash,
true
and false
are "builtins", commands interpreted directly by the shell; in Unix-like systems in general, they also exist as standalone programs on the file system. The difference doesn't matter that much here, but as far as I know, sudo true
will be running the standalone program, not the bash builtin.– IMSoP
Mar 26 at 19:11
31
31
PS: my favourite summaries of
true
and false
are the titles on their man pages: true - do nothing, successfully
and false - do nothing, unsuccessfully
– IMSoP
Mar 26 at 19:14
PS: my favourite summaries of
true
and false
are the titles on their man pages: true - do nothing, successfully
and false - do nothing, unsuccessfully
– IMSoP
Mar 26 at 19:14
3
3
@IMSoP That's deep.
– brainplot
Mar 27 at 12:54
@IMSoP That's deep.
– brainplot
Mar 27 at 12:54
2
2
If
true
didn't exist, the code in the question shows why one might need to invent it! It's a minimal program that can only fail if the system it's on is truly borked. So one can use it to establish if one's access credentials are OK.– nigel222
Mar 27 at 17:22
If
true
didn't exist, the code in the question shows why one might need to invent it! It's a minimal program that can only fail if the system it's on is truly borked. So one can use it to establish if one's access credentials are OK.– nigel222
Mar 27 at 17:22
2
2
In AT&T SYSV Unix, "true" was a shell script /bin/true, which consisted of a large copyright notice in comments...and nothing else.
– Lee Daniel Crocker
Mar 27 at 20:15
In AT&T SYSV Unix, "true" was a shell script /bin/true, which consisted of a large copyright notice in comments...and nothing else.
– Lee Daniel Crocker
Mar 27 at 20:15
|
show 4 more comments
I feel like the accepted answer didn't actually answer your question?
The purpose of doing this is to check that you can actually sudo
.
How this check is performed is via the true
program as explained in the accepted answer.
1
Essentially, this. Alternative could be to check if the user is in sudoers group, but just runningsudo true
is also easy enough of a way, although a bit hacky.
– Sergiy Kolodyazhnyy
Mar 27 at 3:32
3
Note that this also requiressudo
to be installed, so the checks wouldn't be entirely equivalent... you could be in the sudoers group and still not be able to sudo. (This can especially come up if you're e.g. writing a script to setup a new image from a minimal rootfs tarball, which might not have sudo.)
– Mehrdad
Mar 27 at 3:38
1
The OP wants to drop out if you cannot sudo, and get rid of two lines rather than have an else following a noop.
– mckenzm
Mar 27 at 4:10
2
And, conversely, you can also be able tosudo
without being in the sudoers group if you (either personally or as a member of some other group) are listed in/etc/sudoers
. But evensudo true
is not infallible, assudo
access can be granted for only specific commands, so you may be able tosudo true
, but not tosudo something_else
, or vice-versa. There's no iron-clad way to test other than by trying to run the command you actually want to run withsudo
.
– Dave Sherohman
Mar 27 at 14:42
2
Also, you can be in thesudoers
group and not be able tosudo
because thesudoers
group is not listed in thesudoers
file. A group with the four letterssudo
in its name is not a valid indication of whether or not a user in that group can do any particular thing or anything at all usingsudo
.
– jrw32982
Mar 27 at 19:13
|
show 1 more comment
I feel like the accepted answer didn't actually answer your question?
The purpose of doing this is to check that you can actually sudo
.
How this check is performed is via the true
program as explained in the accepted answer.
1
Essentially, this. Alternative could be to check if the user is in sudoers group, but just runningsudo true
is also easy enough of a way, although a bit hacky.
– Sergiy Kolodyazhnyy
Mar 27 at 3:32
3
Note that this also requiressudo
to be installed, so the checks wouldn't be entirely equivalent... you could be in the sudoers group and still not be able to sudo. (This can especially come up if you're e.g. writing a script to setup a new image from a minimal rootfs tarball, which might not have sudo.)
– Mehrdad
Mar 27 at 3:38
1
The OP wants to drop out if you cannot sudo, and get rid of two lines rather than have an else following a noop.
– mckenzm
Mar 27 at 4:10
2
And, conversely, you can also be able tosudo
without being in the sudoers group if you (either personally or as a member of some other group) are listed in/etc/sudoers
. But evensudo true
is not infallible, assudo
access can be granted for only specific commands, so you may be able tosudo true
, but not tosudo something_else
, or vice-versa. There's no iron-clad way to test other than by trying to run the command you actually want to run withsudo
.
– Dave Sherohman
Mar 27 at 14:42
2
Also, you can be in thesudoers
group and not be able tosudo
because thesudoers
group is not listed in thesudoers
file. A group with the four letterssudo
in its name is not a valid indication of whether or not a user in that group can do any particular thing or anything at all usingsudo
.
– jrw32982
Mar 27 at 19:13
|
show 1 more comment
I feel like the accepted answer didn't actually answer your question?
The purpose of doing this is to check that you can actually sudo
.
How this check is performed is via the true
program as explained in the accepted answer.
I feel like the accepted answer didn't actually answer your question?
The purpose of doing this is to check that you can actually sudo
.
How this check is performed is via the true
program as explained in the accepted answer.
answered Mar 26 at 22:32
MehrdadMehrdad
1,41641834
1,41641834
1
Essentially, this. Alternative could be to check if the user is in sudoers group, but just runningsudo true
is also easy enough of a way, although a bit hacky.
– Sergiy Kolodyazhnyy
Mar 27 at 3:32
3
Note that this also requiressudo
to be installed, so the checks wouldn't be entirely equivalent... you could be in the sudoers group and still not be able to sudo. (This can especially come up if you're e.g. writing a script to setup a new image from a minimal rootfs tarball, which might not have sudo.)
– Mehrdad
Mar 27 at 3:38
1
The OP wants to drop out if you cannot sudo, and get rid of two lines rather than have an else following a noop.
– mckenzm
Mar 27 at 4:10
2
And, conversely, you can also be able tosudo
without being in the sudoers group if you (either personally or as a member of some other group) are listed in/etc/sudoers
. But evensudo true
is not infallible, assudo
access can be granted for only specific commands, so you may be able tosudo true
, but not tosudo something_else
, or vice-versa. There's no iron-clad way to test other than by trying to run the command you actually want to run withsudo
.
– Dave Sherohman
Mar 27 at 14:42
2
Also, you can be in thesudoers
group and not be able tosudo
because thesudoers
group is not listed in thesudoers
file. A group with the four letterssudo
in its name is not a valid indication of whether or not a user in that group can do any particular thing or anything at all usingsudo
.
– jrw32982
Mar 27 at 19:13
|
show 1 more comment
1
Essentially, this. Alternative could be to check if the user is in sudoers group, but just runningsudo true
is also easy enough of a way, although a bit hacky.
– Sergiy Kolodyazhnyy
Mar 27 at 3:32
3
Note that this also requiressudo
to be installed, so the checks wouldn't be entirely equivalent... you could be in the sudoers group and still not be able to sudo. (This can especially come up if you're e.g. writing a script to setup a new image from a minimal rootfs tarball, which might not have sudo.)
– Mehrdad
Mar 27 at 3:38
1
The OP wants to drop out if you cannot sudo, and get rid of two lines rather than have an else following a noop.
– mckenzm
Mar 27 at 4:10
2
And, conversely, you can also be able tosudo
without being in the sudoers group if you (either personally or as a member of some other group) are listed in/etc/sudoers
. But evensudo true
is not infallible, assudo
access can be granted for only specific commands, so you may be able tosudo true
, but not tosudo something_else
, or vice-versa. There's no iron-clad way to test other than by trying to run the command you actually want to run withsudo
.
– Dave Sherohman
Mar 27 at 14:42
2
Also, you can be in thesudoers
group and not be able tosudo
because thesudoers
group is not listed in thesudoers
file. A group with the four letterssudo
in its name is not a valid indication of whether or not a user in that group can do any particular thing or anything at all usingsudo
.
– jrw32982
Mar 27 at 19:13
1
1
Essentially, this. Alternative could be to check if the user is in sudoers group, but just running
sudo true
is also easy enough of a way, although a bit hacky.– Sergiy Kolodyazhnyy
Mar 27 at 3:32
Essentially, this. Alternative could be to check if the user is in sudoers group, but just running
sudo true
is also easy enough of a way, although a bit hacky.– Sergiy Kolodyazhnyy
Mar 27 at 3:32
3
3
Note that this also requires
sudo
to be installed, so the checks wouldn't be entirely equivalent... you could be in the sudoers group and still not be able to sudo. (This can especially come up if you're e.g. writing a script to setup a new image from a minimal rootfs tarball, which might not have sudo.)– Mehrdad
Mar 27 at 3:38
Note that this also requires
sudo
to be installed, so the checks wouldn't be entirely equivalent... you could be in the sudoers group and still not be able to sudo. (This can especially come up if you're e.g. writing a script to setup a new image from a minimal rootfs tarball, which might not have sudo.)– Mehrdad
Mar 27 at 3:38
1
1
The OP wants to drop out if you cannot sudo, and get rid of two lines rather than have an else following a noop.
– mckenzm
Mar 27 at 4:10
The OP wants to drop out if you cannot sudo, and get rid of two lines rather than have an else following a noop.
– mckenzm
Mar 27 at 4:10
2
2
And, conversely, you can also be able to
sudo
without being in the sudoers group if you (either personally or as a member of some other group) are listed in /etc/sudoers
. But even sudo true
is not infallible, as sudo
access can be granted for only specific commands, so you may be able to sudo true
, but not to sudo something_else
, or vice-versa. There's no iron-clad way to test other than by trying to run the command you actually want to run with sudo
.– Dave Sherohman
Mar 27 at 14:42
And, conversely, you can also be able to
sudo
without being in the sudoers group if you (either personally or as a member of some other group) are listed in /etc/sudoers
. But even sudo true
is not infallible, as sudo
access can be granted for only specific commands, so you may be able to sudo true
, but not to sudo something_else
, or vice-versa. There's no iron-clad way to test other than by trying to run the command you actually want to run with sudo
.– Dave Sherohman
Mar 27 at 14:42
2
2
Also, you can be in the
sudoers
group and not be able to sudo
because the sudoers
group is not listed in the sudoers
file. A group with the four letters sudo
in its name is not a valid indication of whether or not a user in that group can do any particular thing or anything at all using sudo
.– jrw32982
Mar 27 at 19:13
Also, you can be in the
sudoers
group and not be able to sudo
because the sudoers
group is not listed in the sudoers
file. A group with the four letters sudo
in its name is not a valid indication of whether or not a user in that group can do any particular thing or anything at all using sudo
.– jrw32982
Mar 27 at 19:13
|
show 1 more comment
As I see in this script. It is just checking if sudo is enabled, that is it..
true just returns true.
So in this case if they need to run any command with sudo it checks at start first, asking the password only one time.
The condition works like this: if sudo are executing the true command correctly, it will return true for the if condition, then sudo is enabled and the user typed the password correctly, else you typed the password wrong or sudo is not enabled, the script must not continue.
The other commands do not need to ask sudo password, because your authentication are sucessfully in first time (but this depends on the sudo configuration, so this scripts depends much in the environment configuration)
The 'echo password ok' demonstrate that too. the shell script will not ask the password anymore.
1
The only commands that run through sudo there aresudo true
andsudo -k
. The latter explicitly doesn't require a password. None of the other commands in the script run via sudo, so of course they will not require passwords, regardless of if the authentication was successful the first time.
– ilkkachu
Mar 26 at 15:10
I wrote: "So in this case if they need to run any command with sudo it checks at start first, asking the password only one time. "
– Luciano Andress Martini
Mar 26 at 15:29
add a comment |
As I see in this script. It is just checking if sudo is enabled, that is it..
true just returns true.
So in this case if they need to run any command with sudo it checks at start first, asking the password only one time.
The condition works like this: if sudo are executing the true command correctly, it will return true for the if condition, then sudo is enabled and the user typed the password correctly, else you typed the password wrong or sudo is not enabled, the script must not continue.
The other commands do not need to ask sudo password, because your authentication are sucessfully in first time (but this depends on the sudo configuration, so this scripts depends much in the environment configuration)
The 'echo password ok' demonstrate that too. the shell script will not ask the password anymore.
1
The only commands that run through sudo there aresudo true
andsudo -k
. The latter explicitly doesn't require a password. None of the other commands in the script run via sudo, so of course they will not require passwords, regardless of if the authentication was successful the first time.
– ilkkachu
Mar 26 at 15:10
I wrote: "So in this case if they need to run any command with sudo it checks at start first, asking the password only one time. "
– Luciano Andress Martini
Mar 26 at 15:29
add a comment |
As I see in this script. It is just checking if sudo is enabled, that is it..
true just returns true.
So in this case if they need to run any command with sudo it checks at start first, asking the password only one time.
The condition works like this: if sudo are executing the true command correctly, it will return true for the if condition, then sudo is enabled and the user typed the password correctly, else you typed the password wrong or sudo is not enabled, the script must not continue.
The other commands do not need to ask sudo password, because your authentication are sucessfully in first time (but this depends on the sudo configuration, so this scripts depends much in the environment configuration)
The 'echo password ok' demonstrate that too. the shell script will not ask the password anymore.
As I see in this script. It is just checking if sudo is enabled, that is it..
true just returns true.
So in this case if they need to run any command with sudo it checks at start first, asking the password only one time.
The condition works like this: if sudo are executing the true command correctly, it will return true for the if condition, then sudo is enabled and the user typed the password correctly, else you typed the password wrong or sudo is not enabled, the script must not continue.
The other commands do not need to ask sudo password, because your authentication are sucessfully in first time (but this depends on the sudo configuration, so this scripts depends much in the environment configuration)
The 'echo password ok' demonstrate that too. the shell script will not ask the password anymore.
edited Mar 26 at 15:06
answered Mar 26 at 14:55
Luciano Andress MartiniLuciano Andress Martini
4,2151238
4,2151238
1
The only commands that run through sudo there aresudo true
andsudo -k
. The latter explicitly doesn't require a password. None of the other commands in the script run via sudo, so of course they will not require passwords, regardless of if the authentication was successful the first time.
– ilkkachu
Mar 26 at 15:10
I wrote: "So in this case if they need to run any command with sudo it checks at start first, asking the password only one time. "
– Luciano Andress Martini
Mar 26 at 15:29
add a comment |
1
The only commands that run through sudo there aresudo true
andsudo -k
. The latter explicitly doesn't require a password. None of the other commands in the script run via sudo, so of course they will not require passwords, regardless of if the authentication was successful the first time.
– ilkkachu
Mar 26 at 15:10
I wrote: "So in this case if they need to run any command with sudo it checks at start first, asking the password only one time. "
– Luciano Andress Martini
Mar 26 at 15:29
1
1
The only commands that run through sudo there are
sudo true
and sudo -k
. The latter explicitly doesn't require a password. None of the other commands in the script run via sudo, so of course they will not require passwords, regardless of if the authentication was successful the first time.– ilkkachu
Mar 26 at 15:10
The only commands that run through sudo there are
sudo true
and sudo -k
. The latter explicitly doesn't require a password. None of the other commands in the script run via sudo, so of course they will not require passwords, regardless of if the authentication was successful the first time.– ilkkachu
Mar 26 at 15:10
I wrote: "So in this case if they need to run any command with sudo it checks at start first, asking the password only one time. "
– Luciano Andress Martini
Mar 26 at 15:29
I wrote: "So in this case if they need to run any command with sudo it checks at start first, asking the password only one time. "
– Luciano Andress Martini
Mar 26 at 15:29
add a comment |
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2
If you're going to downvote the question, please could you explain what I can do to improve the question? Is this not the right overflow site?
– Matt Parkins
Mar 26 at 14:47
4
Not sure where the downvotes are coming from; are you trying to negate the statement or nullify the statement? You say you want to get rid of both the true/echo and the "else", so what's your final objective?
– Jeff Schaller♦
Mar 26 at 14:52
1
see stackoverflow.com/q/10552711/537980
– ctrl-alt-delor
Mar 26 at 14:55
1
@ctrl-alt-delor following that link it seems all I need do is put an exclamation mark in front of the sudo and then I can remove both the echo and the else, and now i've tested it, that works, thanks.
– Matt Parkins
Mar 26 at 15:15
2
In passing, you probably ought to redirect the error message to the error stream:
echo "Aborting script" >&2
– Toby Speight
Mar 26 at 17:24