Array parameter expansion: take n-th word from array elements

Array parameter expansion: take n-th word from array elements

[Alexander Groß]

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Hi all,

I would like to parse some output from a command that generates an array of
the following elements:

Main System.Xml.XPath - 4.3
Main System.Xml.XPath.XDocument - 4.3
Test Castle.Core - 4.0
Test FsCheck - 2.9

E.g.

foo=('a interesting - b' 'a also-interesting - c')

I would like to take the second word from each and every of the array
elements (interesting also-interesting). Unfortunately,

print -l ${foo[2]}

prints the second element, 'a also-interesting - c'.

A for loop works:

local -a filtered
for package in $foo; do
  # Split by space and take second word.
  filtered+="${${(s. .)package}[2]}"
done

But I wonder if there is a better way using parameter expansion. Here's
what I came up with so far:
print -l ${${(s. .)foo}[2]}

Unfortunately, it just prints 'interesting'.

Any ideas pointing me in the right direction are greatly appreciated!

Alex
-- 
Alexander Groß
http://therightstuff.de/

Re: Array parameter expansion: take n-th word from array elements

[Nikolay Aleksandrovich Pavlov (ZyX)]

25.06.2017, 15:46, "Alexander Groß" <agross@therightstuff.de>:
> Hi all,
>
> I would like to parse some output from a command that generates an array of
> the following elements:
>
> Main System.Xml.XPath - 4.3
> Main System.Xml.XPath.XDocument - 4.3
> Test Castle.Core - 4.0
> Test FsCheck - 2.9
>
> E.g.
>
> foo=('a interesting - b' 'a also-interesting - c')
>
> I would like to take the second word from each and every of the array
> elements (interesting also-interesting). Unfortunately,
>
> print -l ${foo[2]}
>
> prints the second element, 'a also-interesting - c'.
>
> A for loop works:
>
> local -a filtered
> for package in $foo; do
>   # Split by space and take second word.
>   filtered+="${${(s. .)package}[2]}"
> done
>
> But I wonder if there is a better way using parameter expansion. Here's
> what I came up with so far:
> print -l ${${(s. .)foo}[2]}
>
> Unfortunately, it just prints 'interesting'.
>
> Any ideas pointing me in the right direction are greatly appreciated!

I would just go with ${#} and ${%}:

    % foo=('a interesting - b' 'a also-interesting - c')
    % echo ${${foo% - *}#* }
    interesting also-interesting

>
> Alex
> --
> Alexander Groß
> http://therightstuff.de/

Re: Array parameter expansion: take n-th word from array elements

[Bart Schaefer]

Hmm, I never received Nikolay's message, though I see it on the zsh
archive site.

On Jun 25,  8:34pm, Nikolay Aleksandrovich Pavlov (ZyX) wrote:
}
} 25.06.2017, 15:46, "Alexander Gross" <agross@therightstuff.de>:
} > Hi all,
} >
} > I would like to parse some output from a command that generates an array of
} > the following elements:
} >
} > Main System.Xml.XPath - 4.3
} > Main System.Xml.XPath.XDocument - 4.3
} > Test Castle.Core - 4.0
} > Test FsCheck - 2.9
} >
} > print -l ${${(s. .)foo}[2]}

The only parameter substitution operator that iterates over elements of
an array in the way you want is the ${NAME/PATTERN/REPL} syntax.  If
you setopt extendedglob and use (#m) in the pattern, $MATCH will give
you each of the elements as a string, so you next need to interpret
each string as words.  The (w) subscript modifier does that.

Thus:

    setopt extendedglob
    print -lr -- ${foo/(#m)*/${MATCH[(w)2]}}

Re: Array parameter expansion: take n-th word from array elements

[Nikolay Aleksandrovich Pavlov (ZyX)]

26.06.2017, 02:17, "Bart Schaefer" <schaefer@brasslantern.com>:
> Hmm, I never received Nikolay's message, though I see it on the zsh
> archive site.

I am periodically receiving messages that state that some of the messages sent by list to me bounced. Maybe this problem has the same origin.

>
> On Jun 25, 8:34pm, Nikolay Aleksandrovich Pavlov (ZyX) wrote:
> }
> } 25.06.2017, 15:46, "Alexander Gross" <agross@therightstuff.de>:
> } > Hi all,
> } >
> } > I would like to parse some output from a command that generates an array of
> } > the following elements:
> } >
> } > Main System.Xml.XPath - 4.3
> } > Main System.Xml.XPath.XDocument - 4.3
> } > Test Castle.Core - 4.0
> } > Test FsCheck - 2.9
> } >
> } > print -l ${${(s. .)foo}[2]}
>
> The only parameter substitution operator that iterates over elements of
> an array in the way you want is the ${NAME/PATTERN/REPL} syntax. If
> you setopt extendedglob and use (#m) in the pattern, $MATCH will give
> you each of the elements as a string, so you next need to interpret
> each string as words. The (w) subscript modifier does that.
>
> Thus:
>
>     setopt extendedglob
>     print -lr -- ${foo/(#m)*/${MATCH[(w)2]}}

Re: Array parameter expansion: take n-th word from array elements

[Alexander Groß]

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​> ​
The only parameter substitution operator that iterates over elements of
> an array in the way you want is the ${NAME/PATTERN/REPL} syntax.  If
> you setopt extendedglob and use (#m) in the pattern, $MATCH will give
> you each of the elements as a string, so you next need to interpret
> each string as words.  The (w) subscript modifier does that.

> Thus:
>
>     setopt extendedglob
>     print -lr -- ${foo/(#m)*/${MATCH[(w)2]}}

​Thank you, that was a pointer in the right direction!

​I have another use case for a different output, generated from grep this
time. Some strings may not contain the second word and I want to remove
them. Your suggestion prints the last word ​in this case. Can this be
filtered out as well?

$ foo=('source interesting' '   source​ also-interesting' 'source')
​$ setopt extendedglob​
​$ ​
print -lr -- ${foo/(#m)*/${MATCH[(w)2]}}
interesting
also-interesting
source

Alex
-- 
Alexander Groß
http://therightstuff.de/