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Article #178

Control characters in the shell

#178
From: Karl Heuer
Date: Wed, 21 Mar 1990 20:51
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2079 bytes
From: karl@IMA.IMA.ISC.COM (Karl Heuer)

This came up in comp.org.usrgroup, but I think this is a better place.

Observation: The shell, considered as a programming language, has a string
datatype but does not have adequate facilities for embedding nonprinting
characters in a string constant.  As a result, several commands (date, echo,
paste, prs, stty, tr) have evolved (largely incompatible) notations for
translating escape sequences into such nonprinting characters.

Opinion: A much cleaner solution would be to have a simple shell syntax which
causes the nonprinting characters to be embedded into the argument string, so
that it would be transparent to the program.

Proposal: Reserve $\ (dollar-backslash) as a new entity that begins a C-like
escape, so we would have $\a $\b $\t $\n $\v $\f $\r, octal escapes like
$\177, and hex escapes like $\x7F.

Alternative proposal (from a suggestion by Eric Gisin, eric@mks.com): make a
new string quoting mechanism, $"...", which is just like "..." except that, in
addition to the four current backslash escapes \$ \` \" \\ that are permitted
inside double quotes, all the C-like escapes \a etc. would be recognized.

I'm told that the POSIX shell does not address this perceived deficiency.  I
hope it's not too late for this to be corrected.

Karl W. Z. Heuer (karl@ima.ima.isc.com or harvard!ima!karl), The Walking Lint

Volume-Number: Volume 19, Number 20
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References: <2567@mbf.UUCP> <EQ.1811xds13@ficc.uu.net> <16108@haddock.ima.isc.com> <1990Mar8.171918.16011@mks.com> <16184@haddock.ima.isc.com>

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Path: arc1-ca.pugleaf.net!utzoo!attcan!uunet!cs.utexas.edu!longway!std-unix
From: karl@IMA.IMA.ISC.COM (Karl Heuer)
Newsgroups: comp.std.unix
Subject: Control characters in the shell
Keywords: Draft 9 shell meta standard shell
Message-ID: <589@longway.TIC.COM>
Date: 21 Mar 90 20:51:46 GMT
References: <2567@mbf.UUCP> <EQ.1811xds13@ficc.uu.net> <16108@haddock.ima.isc.com> <1990Mar8.171918.16011@mks.com> <16184@haddock.ima.isc.com>
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