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Re: Syntax Question...

From: Stephane CHAZELAS
Subject: Re: Syntax Question...
Date: Wed, 28 Mar 2012 18:26:01 -0000
User-agent: slrn/pre1.0.0-18 (Linux)

2011-08-17, 08:24(-04), Greg Wooledge:
> On Tue, Aug 16, 2011 at 03:41:19PM -0700, Linda Walsh wrote:
>> Ken Irving wrote:
>> >Maybe this?
>> >    today_snaps=( ${snap_prefix} )
>>   but as you mention, that will put them into an array....sorry "imprecise
>> terminology".... list for me is some number of objects in a string 
>> separated by some
>> separator.
> This is an extremely bad idea.  Legacy Bourne shell code from the
> 1980s kind of bad -- from the horrible days before we *had* arrays
> in shells.  How are you going to handle filenames with spaces in them?
> With newlines in them?  With commas in them?  With colons in them?  Tabs?
> DEL characters?  Those are all valid in filenames.  Any delimiter you
> can *put* in a shell string is also a valid character in a filename (or
> at least in a pathname, which eliminates the possibility of using slash).

In this code:

today_snaps=( ${snap_prefix} )

With the default value of IFS in bash and without globbing
disabled, the problematic characters are SPC, TAB, NL, *, ?, [
and potentially more if you have extended globbing enabled.

If $snap_prefix is meant to be space delimited, then you can
make it a bit safer by doing:

IFS=" "
set -f
today_snaps=( $snap_prefix )

NL is a good delimited because it's rare in filenames (but are
allowed, so if the data is foreign and security is a concern,
not an option) and you can also pass the list to line-based
(text_ utilities

a2 b2'

set -f
set -- $var

Or a_vars=$(printf '%s\n' "$var" | grep '^a')


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