From: "Bart Schaefer" <schaefer@candle.brasslantern.com>
To: "Andrej Borsenkow" <borsenkow.msk@sni.de>,
"ZSH workers mailing list" <zsh-workers@sunsite.auc.dk>
Subject: Re: Speed of ZSH
Date: Fri, 21 May 1999 10:18:36 +0000 [thread overview]
Message-ID: <990521101836.ZM9723@candle.brasslantern.com> (raw)
In-Reply-To: <001a01bea361$994a2140$21c9ca95@mow.siemens.ru>
On May 21, 12:11pm, Andrej Borsenkow wrote:
} Subject: Speed of ZSH
}
} I recently needed to do a quick prototyping, and selected zsh just for the
} easy programming. The task was: I get a file with records of length 2040
} characters and need to extract several (~100) fixed width fields and write
} them out separated by tabs. I had a list of fields in the form n1-n2, so I
} just vi'ed them :-) to get $line[n1,n2].
}
} The problems I got were:
}
} 1. I found, that it is near to impossible to ``read'' line without breaking
} it on IFS. ``read -k'' did not work :-(
You have to combine it with -u to get the desired effect, and you need
to use -r to prevent backslash-interpretation. I tried to explain about
this in my rewrite of the "read" info in 3.1.5, but maybe I didn't do a
good enough job. (It's also a bit odd that a space must precede the
argument to -k and must not precede the argument to -u, at least as the
3.0.5 code stands.)
read -ru0 -k 2040 block < file
} 2. It is impossible to ``print'' arguments separated by user defined string
} (only NL or NUL).
Unless there are embedded NULs in the input, just use "tr":
print -rN -- "$block[n1,n2]" "$block[n3,n4]" ... | tr '\0' '\11'
But:
} I had to make an array out of fields, and then print it
} with explicit join:
}
} fields=( $line[n1,n2] ...)
} print ${(j/\t/)fields}
If you're already spelling it all out like that, why not use a single
quoted string and put in the tabs yourself?
print -r -- "$block[n1,n2] $block[n3,n4] ..."
It won't be pretty, but it'll get the job done.
} After doing it I found, that ZSH needs several seconds for a file with 28
} records! That is really too much for such a simple task. I suspect, the
} reason is constant reallocation of memory when first array is created
} (remember, it has about 100 elements) and then when it is joined.
You're probably right. There are good and bad ways to write programs in
any language. Simply doing the read/print isn't that slow (though about
8 times slower than dd, look at the user seconds):
zagzig[31] time while read -ru0 -k 2040 block ; do print -r -- "$block"; done < /etc/termcap | dd bs=2040 of=/dev/null
213+198 records in
213+198 records out
while read -ru0 -k 2040 block; do; print -r -- "$block"; done < /etc/termcap 0.79s user 0.07s system 93% cpu 0.917 total
dd bs=2040 of=/dev/null 0.01s user 0.02s system 3% cpu 0.875 total
--
Bart Schaefer Brass Lantern Enterprises
http://www.well.com/user/barts http://www.brasslantern.com
prev parent reply other threads:[~1999-05-21 10:19 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-05-21 8:11 Andrej Borsenkow
1999-05-21 10:18 ` Bart Schaefer [this message]
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