From: Marc Chantreux <eiro@phear.org>
To: Ray Andrews <rayandrews@eastlink.ca>
Cc: zsh-users@zsh.org
Subject: Re: real time alias?
Date: Thu, 15 Mar 2018 22:44:50 +0100 [thread overview]
Message-ID: <20180315214450.sle4bsb3ab6dt56i@prometheus.u-strasbg.fr> (raw)
In-Reply-To: <9001d78e-91fd-8505-518f-27247462d3c2@eastlink.ca>
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
next prev parent reply other threads:[~2018-03-15 21:45 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-15 17:51 Ray Andrews
2018-03-15 17:57 ` Jérémie Roquet
2018-03-15 18:13 ` Ray Andrews
2018-03-15 21:44 ` Marc Chantreux [this message]
2018-03-15 21:46 ` Marc Chantreux
2018-03-16 17:19 ` Justin M Wozniak
2018-03-16 17:41 ` Ray Andrews
2018-03-17 16:00 ` Marc Chantreux
2018-03-16 17:51 ` Marc Chantreux
2018-03-16 16:47 ` Ray Andrews
2018-03-16 17:41 ` Marc Chantreux
2018-03-16 18:13 ` Bart Schaefer
2018-03-16 18:56 ` Ray Andrews
2018-03-18 23:01 ` Bart Schaefer
2018-03-19 0:05 ` Ray Andrews
2018-03-17 23:17 ` Bart Schaefer
[not found] <98aa0638-97ed-dfe0-8dd2-39129d02c084__39937.2481661432$1521136270$gmane$org@eastlink.ca>
2018-03-17 22:47 ` Stephane Chazelas
2018-03-18 3:20 ` Ray Andrews
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