how do I get the last argument from a list of arguments?

how do I get the last argument from a list of arguments?

[TJ Luoma]

I’m trying to learn better ways of dealing with arguments given to a
function, because I am sure that I am not doing it the most efficient
way.

For example, if I want to process a series of args, I usually use a
loop like this:

for FOO in "$@"
do
     case "$FOO" in
          -t|--to)
               shift
               TO="$1"
               shift
          ;;

          -v|--verbose)
               VERBOSE='yes'
          shift
          ;;

          -*|--*)
               echo " $NAME [warning]: Don't know what to do with arg: $1"
               shift
          ;;

     esac

done # for args

That has worked OK for what I've needed to do, but now I'm trying to
create two functions which I will use in place of 'cp' and 'mv' and I
need to be able to find the _last_ argument (the destination) before I
process all the rest of the args.

The only way that I can think of to get the last argument is to do
something like this

     LAST=`echo "$@" | awk '{print $NF}'`

but that made me wonder if there wasn’t a better way.

Note that this does not need to be 'portable' at all -- I will happily
use any zsh-specific features which may exist, as long as it works in
5.0.2 (which is what comes with OS X).

Thanks!

TjL

Re: how do I get the last argument from a list of arguments?

[Kurtis Rader]

[-- Attachment #1: Type: text/plain, Size: 1796 bytes --]

See the description of the *${name:offset} *syntax in *man zshexpn*. Note
the space between the colon and minus-sign is required to disambiguate it
from the "var:-default" syntax.

function lastarg() {
    print "${@[-1]}"
    print "${@: -1}"
}

lastarg 1 2 3


On Mon, Jul 7, 2014 at 2:06 PM, TJ Luoma <luomat@gmail.com> wrote:

> I’m trying to learn better ways of dealing with arguments given to a
> function, because I am sure that I am not doing it the most efficient
> way.
>
> For example, if I want to process a series of args, I usually use a
> loop like this:
>
> for FOO in "$@"
> do
>      case "$FOO" in
>           -t|--to)
>                shift
>                TO="$1"
>                shift
>           ;;
>
>           -v|--verbose)
>                VERBOSE='yes'
>           shift
>           ;;
>
>           -*|--*)
>                echo " $NAME [warning]: Don't know what to do with arg: $1"
>                shift
>           ;;
>
>      esac
>
> done # for args
>
> That has worked OK for what I've needed to do, but now I'm trying to
> create two functions which I will use in place of 'cp' and 'mv' and I
> need to be able to find the _last_ argument (the destination) before I
> process all the rest of the args.
>
> The only way that I can think of to get the last argument is to do
> something like this
>
>      LAST=`echo "$@" | awk '{print $NF}'`
>
> but that made me wonder if there wasn’t a better way.
>
> Note that this does not need to be 'portable' at all -- I will happily
> use any zsh-specific features which may exist, as long as it works in
> 5.0.2 (which is what comes with OS X).
>
> Thanks!
>
> TjL
>



-- 
Kurtis Rader
Caretaker of the exceptional canines Junior and Hank

Re: how do I get the last argument from a list of arguments?

[Peter Stephenson]

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TJ Luoma wrote:
> That has worked OK for what I've needed to do, but now I'm trying to
> create two functions which I will use in place of 'cp' and 'mv' and I
> need to be able to find the _last_ argument (the destination) before I
> process all the rest of the args.
> 
> The only way that I can think of to get the last argument is to do
> something like this
> 
>      LAST=`echo "$@" | awk '{print $NF}'`
> 
> but that made me wonder if there wasn’t a better way.

The arguments are available as the array argv, so use $argv[-1].

-- 
Peter Stephenson <p.w.stephenson@ntlworld.com>
Web page now at http://homepage.ntlworld.com/p.w.stephenson/

Re: how do I get the last argument from a list of arguments?

[Bart Schaefer]

On Jul 7,  5:06pm, TJ Luoma wrote:
}
} I'm trying to learn better ways of dealing with arguments given to a
} function, because I am sure that I am not doing it the most efficient
} way.

If the arguments are defined in a fairly regular way, zparseopts is
probably the fastest method.

E.g. your "for FOO" loop becomes something like:

    local -A opts
    zparseopts -A opts -D -E -M t:=-to -to: v=-verbose -verbose

    while [[ $1 = -* ]]
    do
	echo " $NAME [warning]: Don't know what to do with arg: $1"
	shift
    done

    # You can skip this part and use $opts[] directly, but:
    local TO=$opts[--to] VERBOSE=${opts[--verbose]+yes}

With the -E -D -K flags you can call zparseopts multiple times if you
want to (-E means skip over unspecified options, -D means remove the
specified ones, and -K means to keep the results of previous calls).

} That has worked OK for what I've needed to do, but now I'm trying to
} create two functions which I will use in place of 'cp' and 'mv' and I
} need to be able to find the _last_ argument (the destination) before I
} process all the rest of the args.

See Kurtis' reply regarding how to access arrays from the tail end.
However, GNU cp/mv both take a --target= option so the directory name
needn't be the last argument.  So you could do something like

    zparseopts -E -D -A opts --target:
    if [[ -z $opts[--target] ]]
    then
      opts[--target]=$@[-1]
      shift -p
    fi

That "shift -p" means to "pop" the last argument, in the "cp" example
leaving $@ holding only the file names you are interested in copying.

Re: how do I get the last argument from a list of arguments?

[zzapper]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
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TJ Luoma <luomat@gmail.com> wrote in
news:CADjGqHuALx7Ue3Ei3s7XvT_pHWxECo2rt=BNegPO5Fwcuge2LQ@mail.gmail.com: 

> I’m trying to learn better ways of dealing with arguments given to a
> function, because I am sure that I am not doing it the most efficient
> way.
Similar to Kurtis

p()
{
echo "last ${@[-1]}"
echo "2nd last ${@[-2]}"
}
p a b c d




--
zzapper
https://twitter.com/dailyzshtip

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Re: how do I get the last argument from a list of arguments?

[zzapper]

zzapper <david@rayninfo.co.uk> wrote in 
news:XnsA3648D0E647C1davidrayninfocouk@80.91.229.13:

> p()
> {
> echo "last ${&#64;[-1]}"
> echo "2nd last ${&#64;[-2]}"
> }
> p a b c d


just trying to see if i can display the at sign correctly by using an html 
entity & #64 ;
-- 
zzapper
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Re: how do I get the last argument from a list of arguments?

[Roman Neuhauser]

# david@rayninfo.co.uk / 2014-07-08 14:11:40 +0000:
> zzapper <david@rayninfo.co.uk> wrote in 
> news:XnsA3648D0E647C1davidrayninfocouk@80.91.229.13:
> 
> > p()
> > {
> > echo "last ${&#64;[-1]}"
> > echo "2nd last ${&#64;[-2]}"
> > }
> > p a b c d
> 
> 
> just trying to see if i can display the at sign correctly by using an html 
> entity & #64 ;

your email had no MIME information let alone the text/html content type.

-- 
roman

Re: how do I get the last argument from a list of arguments?

[zzapper]

Roman Neuhauser <neuhauser@sigpipe.cz> wrote in
news:20140708150621.GJ11492@isis.sigpipe.cz: 

> # david@rayninfo.co.uk / 2014-07-08 14:11:40 +0000:

 
>> just trying to see if i can display the at sign correctly by using an
>> html entity & #64 ;
> 
> your email had no MIME information let alone the text/html content
> type. 
> 

Roman
Sorry for confusion was only on the 
http://news.gmane.org/gmane.comp.shells.zsh.user

website where they automatically replace all @ with < at> 

-- 
zzapper
https://twitter.com/dailyzshtip

---
This email is free from viruses and malware because avast! Antivirus protection is active.
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Re: how do I get the last argument from a list of arguments?

[Roman Neuhauser]

# david@rayninfo.co.uk / 2014-07-08 15:25:31 +0000:
> Sorry for confusion was only on the 
> http://news.gmane.org/gmane.comp.shells.zsh.user
> 
> website where they automatically replace all @ with < at> 

yeah, gmane sucks.

-- 
roman