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Re: real time alias?
On Thu, Mar 15, 2018 at 10:44:50PM +0100, Marc Chantreux wrote:
> hello,
>
> > > > If a function calls an alias, if the alias changes, the function must be
> > > > resourced, yes? That makes nothing but sense sincethe alias is what it is
> > > > at sourcing. An executed script uses the alias in 'real time'. But, is
> > > > there a way to make a function also use the real time value of an alias?
>
> > Sure, I was just wondering if it was possible at all with an alias.
>
> my advice is: see aliases as macro: don't use it as long as you can
> achieve things with functions. one of the reasons is aliases can be used
> after a variable expansion and so you can get some surprising behaviors.
>
> rip () {
> print $1 wrote
> "$@"
> print then $1 died
> }
> alias stephen='print a brief history of time'
> rip stephen hawkings
>
> then your universe colapse
>
> stephen wrote
> rip:2: command not found: stephen
> then stephen died
>
> but
>
> rip () {
> print $1 wrote
> "$@"
> print then $1 died
> }
> stephen () print a brief history of time
> rip stephen hawkings
>
> gives you a good reading advice
>
> stephen wrote
> a brief history of time
> then stephen died
>
> so when are aliases useful? well ... basically when you need something
> like a preprocessor. for example if you have a set of functions where
> the first arguments are always the same, you can write an alias for it:
>
> alias user_='local ns=${1?namespace of the user expected} \
> id=${2?the id of the user expected}'
>
> showid () { user_; print user id is $id }
> showns () { user_; print user ns is $ns }
> showid
>
> warns you
>
> showid: 1: namespace of the user expected
>
> another example from uze.zsh (https://github.com/zsh-uze)
>
> warn_ () { local r=$?; print -u2 "$*"; return $r }
> die_ () { local r=$?; print -u2 "$*"; exit $r }
> alias warn='warn_ at $0 line $LINENO, warning:'
> alias ...='{warn unimplemented; return 255}'
> alias die='die_ died at $0 line $LINENO:'
>
> now i can write
>
> allowed () false
>
> do_stuff () {
> if {allowed} {
> print i do stuff
> } else {
> # what to do then ?
> ...
> }
> }
>
> do_stuff
>
> so i have this message:
>
> at do_stuff line 5, warning: unimplemented
>
> hth,
> marc
>
> > you ask, there might be some option or something whereby a function is
> > instructed to grab an alias at runtime sorta the way the value of a variable
> > is grabbed at runtime.
>
> you can use both functions and arrays
>
> show () {
> print "hello, i'm a particle and i'm"
> position
> }
> position () print here and there
> show
> position () print elsewhere
> show
>
> gives
>
> hello, i'm a particle and i'm
> here and there
> hello, i'm a particle and i'm
> elsewhere
>
> also
>
> show () print -l "hello, i'm a particle and i'm" $position
> position=( here and there )
> show
> position=( elsewhere )
> show
>
> gives
>
> hello, i'm a particle and i'm
> here
> and
> there
> hello, i'm a particle and i'm
> elsewhere
>
> don't forget that in crontrary of other shells, zsh takes arrays and
> word spliting seriously so you can store a whole command into an array.
> this is lovely when you build one step by step
>
> academic () true
> faster () true
> dryrun () true
>
> dryrun && compiles=( print cc )
> || compiles=( cc )
>
> academic && compiles+=( -Wall -std=c99 )
> faster && compiles+=( -O2 )
> compiles+=( $src $dest )
> $compiles
>
> hth
> marc
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