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On Fri, Jun 15, 2012 at 10:05 AM, Peter Stuge <peter@×××××.se> wrote: |
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> Fabian Groffen wrote: |
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>> > > >>> + if [[ ! -n $(egetent passwd "${euser}") ]] ; then |
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>> > > >> |
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>> > > >> "! -n" -> "-z" |
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>> > > > |
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>> > > > Does the $() argument ever need to be double quoted, or do all |
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>> > > > versions of bash actually have the string argument optional even |
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>> > > > though that's not what the man page reads? |
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>> > > |
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>> > > Ever? Yes, but only if what is being returned can contain spaces |
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>> > |
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>> > Sorry, I should have mentioned that I had the case of the empty |
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>> > string in mind. |
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>> |
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>> Here for the same reason, the difference between [[ and [ is essential. |
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> |
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> It's not clear to me why? |
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> |
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> [] is shorthand for test. Both test and [[]] in my man bash read: |
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> |
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> --8<-- |
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> Expressions are composed of the primaries described .. under |
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> CONDITIONAL EXPRESSIONS. |
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> -->8-- |
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> |
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> There it says: |
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> --8<-- |
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> Conditional expressions are used by the [[ compound command and |
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> the test and [ builtin commands |
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> -->8-- |
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> |
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> and: |
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> --8<-- |
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> -z string |
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> True if the length of string is zero. |
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> string |
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> -n string |
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> True if the length of string is non-zero. |
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> -->8-- |
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> |
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> ..which does not at all make it clear that the string is actually |
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> optional? |
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> |
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> Under Command Substitution it says: |
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> --8<-- |
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> Embedded newlines are not deleted, but they may be removed during |
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> word splitting. |
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> .. |
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> If the substitution appears within double quotes, word splitting |
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> and pathname expansion are not performed on the results. |
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> -->8-- |
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> |
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> ..confirming that there is some processing of the substitution. |
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> |
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> |
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> I also did the tests before asking the question. I'm not trying to |
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> say that the code doesn't work on my system. I'm asking if it will |
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> work the same on every version of bash, in spite of what seems to |
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> be a conflict between real world and documentation. |
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> |
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> |
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> //Peter |
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|
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Word splitting does not occur within double brackets. This is |
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documented in the bash manual. |
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|
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http://www.gnu.org/software/bash/manual/bashref.html#Conditional-Constructs |
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|
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This causes empty output from a command substitution within double |
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brackets to be treated as a zero-length string. |
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