On Jan 26, 2012, at 11:30 AM, Jens Alfke wrote:
> To work around this I suggest using single-quotes instead, and preprocessing
> the string to insert a backslash in front of any exclamation point or
> single-quote. I *think* that will be enough.
After a single quote, the *only* character that has a special meaning is
another single quote, which ends the quotation. Double quotes, back slashes,
dollar signs, exclamation marks, et al. have absolutely no special significance
between single quotes..
Thus, the simplest way to safely quote an arbitrary string is to preprocess the
string to replace each single quote (') with the sequence single quote,
backslash, single quote, single quote ('\''), and then wrap the resulting
string in single quotes.
As an (unnecessary) refinement, scan that sequence again, replacing each
sequence of three consecutive single quotes with one, to shorten the string
that results when the original string contained consecutive single quotes. As
another (unnecessary) refinement, pre-scan the original string to see if it
contains only safe characters, in which case no quoting needs to be done at
all. It's probably not worth bothering to do either of these.
Almost as easy to program, but generally producing longer quoted strings, is to
prepend a backslash to any character that is not a lowercase letter or a digit.
Do not wrap the resulting string in any kind of quotes. (Non-ASCII characters
are never special to the shell, but I'm not sure what would happen if you
inserted backslashes in the middle of a multi-byte character, nor whether the
behavior will change in later versions of the shell, so be sure you're
prepending backslashes to characters, not bytes.)
-Ron Hunsinger
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