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.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

5

1

I would like to check whether a user is in a certain group via

[[ "$(getent group groupname)" =~ busernameb ]]

but this does not work (bash 5.0.3) although the following works:

getent group groupname | grep -E "busernameb"

I noticed that the backslashes appear to be swallowed at some place

bash -cx '[[ "$(getent group groupname)" =~ busernameb ]]'
++ getent group groupname
+ [[ groupname:x:24:username =~ busernameb ]]

but this could also be an effect of -x.

Can anyone clear this up? :-)

bash regular-expression

share|improve this question

asked May 23 at 11:19

SuuuehgiSuuuehgi

671511

add a comment | 

5

1

I would like to check whether a user is in a certain group via

[[ "$(getent group groupname)" =~ busernameb ]]

but this does not work (bash 5.0.3) although the following works:

getent group groupname | grep -E "busernameb"

I noticed that the backslashes appear to be swallowed at some place

bash -cx '[[ "$(getent group groupname)" =~ busernameb ]]'
++ getent group groupname
+ [[ groupname:x:24:username =~ busernameb ]]

but this could also be an effect of -x.

Can anyone clear this up? :-)

bash regular-expression

share|improve this question

asked May 23 at 11:19

SuuuehgiSuuuehgi

671511

add a comment | 

I would like to check whether a user is in a certain group via

[[ "$(getent group groupname)" =~ busernameb ]]

but this does not work (bash 5.0.3) although the following works:

getent group groupname | grep -E "busernameb"

I noticed that the backslashes appear to be swallowed at some place

bash -cx '[[ "$(getent group groupname)" =~ busernameb ]]'
++ getent group groupname
+ [[ groupname:x:24:username =~ busernameb ]]

but this could also be an effect of -x.

Can anyone clear this up? :-)

bash regular-expression

share|improve this question

asked May 23 at 11:19

SuuuehgiSuuuehgi

671511

[[ "$(getent group groupname)" =~ busernameb ]]

getent group groupname | grep -E "busernameb"

bash -cx '[[ "$(getent group groupname)" =~ busernameb ]]'
++ getent group groupname
+ [[ groupname:x:24:username =~ busernameb ]]

share|improve this question

asked May 23 at 11:19

SuuuehgiSuuuehgi

671511

share|improve this question

asked May 23 at 11:19

SuuuehgiSuuuehgi

671511

asked May 23 at 11:19

SuuuehgiSuuuehgi

671511

asked May 23 at 11:19

SuuuehgiSuuuehgi

671511

1 Answer
1

active

oldest

votes

10

In bash, is a quoting operator like ' and ". So:

[[ "$(getent group groupname)" =~ busernameb ]]

is the same as:

[[ "$(getent group groupname)" =~ 'b'username'b' ]]

Since bash 3.2, bash makes sure than when you quote a character in a regexp, it removes its special meaning as a regexp operator if it had one (which is not the case of b).

In bash 3.1, you would have been able to do:

[[ "$(getent group groupname)" =~ 'busernameb' ]]

And you can still do if you turn on the bash31 option or set $BASH_COMPAT to 3.1. That would also work in zsh.

That would have worked on systems where the system extended regular expression library supports that b non-standard extension (like on recent GNU systems).

In bash 3.2 and above, that doesn't work because by quoting the , bash removes the specialness of as a regex operator (in effect it calls the regex library with \busername\b.

What you can do though is write it:

regexp='<username>' # here using the slightly more portable < > instead of b
[[ "$(getent group groupname)" =~ $regexp ]] # make sure $regexp is *not* quoted

Then it would work with both bash 3.1 and bash 3.2+ (and zsh and ksh93). See How does storing the regular expression in a shell variable avoid problems with quoting characters that are special to the shell? for more details on that.

Here though, I'd use standard sh syntax and do:

group=groupname
user=username

group_definition=$(getent -- group "$group") || exit
case ,$group_definition##*:, in
 (*,"$user",*) printf '%sn' "$user is in the $group groupn"
esac

Which also works more reliably if the user name contains regexp operators (. is common in user names) or the user name happens to be the same as the group name.

share|improve this answer

edited May 23 at 12:55

answered May 23 at 11:35

Stéphane ChazelasStéphane Chazelas

321k57612982

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks a lot! This change in 3.2 seems quite unfortunate regarding the =~ operator considering that you always have to create a regexp-variable first.
  
  – Suuuehgi
  May 23 at 12:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Suuuehgi, yes, I kind of agree. See also my latest edit and Why isn't `|` treated literally in a glob pattern? or Which regular expression methods to validate input could be used in shell scripting? or osdn.net/projects/yash/ticket/39094
  
  – Stéphane Chazelas
  May 23 at 13:03
  
  

  
  
  
  

add a comment | 

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10

In bash, is a quoting operator like ' and ". So:

[[ "$(getent group groupname)" =~ busernameb ]]

is the same as:

[[ "$(getent group groupname)" =~ 'b'username'b' ]]

Since bash 3.2, bash makes sure than when you quote a character in a regexp, it removes its special meaning as a regexp operator if it had one (which is not the case of b).

In bash 3.1, you would have been able to do:

[[ "$(getent group groupname)" =~ 'busernameb' ]]

And you can still do if you turn on the bash31 option or set $BASH_COMPAT to 3.1. That would also work in zsh.

That would have worked on systems where the system extended regular expression library supports that b non-standard extension (like on recent GNU systems).

In bash 3.2 and above, that doesn't work because by quoting the , bash removes the specialness of as a regex operator (in effect it calls the regex library with \busername\b.

What you can do though is write it:

regexp='<username>' # here using the slightly more portable < > instead of b
[[ "$(getent group groupname)" =~ $regexp ]] # make sure $regexp is *not* quoted

Then it would work with both bash 3.1 and bash 3.2+ (and zsh and ksh93). See How does storing the regular expression in a shell variable avoid problems with quoting characters that are special to the shell? for more details on that.

Here though, I'd use standard sh syntax and do:

group=groupname
user=username

group_definition=$(getent -- group "$group") || exit
case ,$group_definition##*:, in
 (*,"$user",*) printf '%sn' "$user is in the $group groupn"
esac

Which also works more reliably if the user name contains regexp operators (. is common in user names) or the user name happens to be the same as the group name.

share|improve this answer

edited May 23 at 12:55

answered May 23 at 11:35

Stéphane ChazelasStéphane Chazelas

321k57612982

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks a lot! This change in 3.2 seems quite unfortunate regarding the =~ operator considering that you always have to create a regexp-variable first.
  
  – Suuuehgi
  May 23 at 12:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Suuuehgi, yes, I kind of agree. See also my latest edit and Why isn't `|` treated literally in a glob pattern? or Which regular expression methods to validate input could be used in shell scripting? or osdn.net/projects/yash/ticket/39094
  
  – Stéphane Chazelas
  May 23 at 13:03
  
  

  
  
  
  

add a comment | 

10

In bash, is a quoting operator like ' and ". So:

[[ "$(getent group groupname)" =~ busernameb ]]

is the same as:

[[ "$(getent group groupname)" =~ 'b'username'b' ]]

Since bash 3.2, bash makes sure than when you quote a character in a regexp, it removes its special meaning as a regexp operator if it had one (which is not the case of b).

In bash 3.1, you would have been able to do:

[[ "$(getent group groupname)" =~ 'busernameb' ]]

And you can still do if you turn on the bash31 option or set $BASH_COMPAT to 3.1. That would also work in zsh.

That would have worked on systems where the system extended regular expression library supports that b non-standard extension (like on recent GNU systems).

In bash 3.2 and above, that doesn't work because by quoting the , bash removes the specialness of as a regex operator (in effect it calls the regex library with \busername\b.

What you can do though is write it:

regexp='<username>' # here using the slightly more portable < > instead of b
[[ "$(getent group groupname)" =~ $regexp ]] # make sure $regexp is *not* quoted

Then it would work with both bash 3.1 and bash 3.2+ (and zsh and ksh93). See How does storing the regular expression in a shell variable avoid problems with quoting characters that are special to the shell? for more details on that.

Here though, I'd use standard sh syntax and do:

group=groupname
user=username

group_definition=$(getent -- group "$group") || exit
case ,$group_definition##*:, in
 (*,"$user",*) printf '%sn' "$user is in the $group groupn"
esac

Which also works more reliably if the user name contains regexp operators (. is common in user names) or the user name happens to be the same as the group name.

share|improve this answer

edited May 23 at 12:55

answered May 23 at 11:35

Stéphane ChazelasStéphane Chazelas

321k57612982

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks a lot! This change in 3.2 seems quite unfortunate regarding the =~ operator considering that you always have to create a regexp-variable first.
  
  – Suuuehgi
  May 23 at 12:12
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Suuuehgi, yes, I kind of agree. See also my latest edit and Why isn't `|` treated literally in a glob pattern? or Which regular expression methods to validate input could be used in shell scripting? or osdn.net/projects/yash/ticket/39094
  
  – Stéphane Chazelas
  May 23 at 13:03
  
  

  
  
  
  

add a comment | 

In bash, is a quoting operator like ' and ". So:

[[ "$(getent group groupname)" =~ busernameb ]]

is the same as:

[[ "$(getent group groupname)" =~ 'b'username'b' ]]

Since bash 3.2, bash makes sure than when you quote a character in a regexp, it removes its special meaning as a regexp operator if it had one (which is not the case of b).

In bash 3.1, you would have been able to do:

[[ "$(getent group groupname)" =~ 'busernameb' ]]

And you can still do if you turn on the bash31 option or set $BASH_COMPAT to 3.1. That would also work in zsh.

That would have worked on systems where the system extended regular expression library supports that b non-standard extension (like on recent GNU systems).

In bash 3.2 and above, that doesn't work because by quoting the , bash removes the specialness of as a regex operator (in effect it calls the regex library with \busername\b.

What you can do though is write it:

regexp='<username>' # here using the slightly more portable < > instead of b
[[ "$(getent group groupname)" =~ $regexp ]] # make sure $regexp is *not* quoted

Then it would work with both bash 3.1 and bash 3.2+ (and zsh and ksh93). See How does storing the regular expression in a shell variable avoid problems with quoting characters that are special to the shell? for more details on that.

Here though, I'd use standard sh syntax and do:

group=groupname
user=username

group_definition=$(getent -- group "$group") || exit
case ,$group_definition##*:, in
 (*,"$user",*) printf '%sn' "$user is in the $group groupn"
esac

Which also works more reliably if the user name contains regexp operators (. is common in user names) or the user name happens to be the same as the group name.

share|improve this answer

edited May 23 at 12:55

answered May 23 at 11:35

Stéphane ChazelasStéphane Chazelas

321k57612982

[[ "$(getent group groupname)" =~ busernameb ]]

[[ "$(getent group groupname)" =~ 'b'username'b' ]]

[[ "$(getent group groupname)" =~ 'busernameb' ]]

regexp='<username>' # here using the slightly more portable < > instead of b
[[ "$(getent group groupname)" =~ $regexp ]] # make sure $regexp is *not* quoted

group=groupname
user=username

group_definition=$(getent -- group "$group") || exit
case ,$group_definition##*:, in
 (*,"$user",*) printf '%sn' "$user is in the $group groupn"
esac

share|improve this answer

edited May 23 at 12:55

answered May 23 at 11:35

Stéphane ChazelasStéphane Chazelas

321k57612982

answered May 23 at 11:35

Stéphane ChazelasStéphane Chazelas

321k57612982

answered May 23 at 11:35

Stéphane ChazelasStéphane Chazelas

321k57612982