[mdlug] Evil eval

[Jeff Hanson]

Thanks.  Somebody on Reddit told me the same thing.  I've never used them
before.  The quotes worked but I just couldn't understand why the escapes
didn't for the second variable in the echo line.

On Thu, Oct 2, 2014 at 6:28 AM, Carl T. Miller <carl at carltm.com> wrote:

> Jeff Hanson wrote:
> > An eval echo statement is not working as I would expect.  The first
> > derived
> > variable name works with the suffix quoted or escaped.  The second only
> > works quoted.  Since it behaves the same in both Bash and Dash I'm
> > assuming
> > it's my fault.  Example with various combinations in the output:
> >
> > #! /bin/sh
> > test1a_uc="A"
> > test1b_uc="B"
> > test1c_uc="C"
> >
> > for varname in test1a test1b test1c; do
> >     eval $varname"_lc"=\$\(echo "\$$varname""_uc | tr '[:upper:]'
> > '[:lower:]'"\)
> > done
> >
> > # Output
> > echo "Quotes both:"
> > for varname in test1a test1b test1c; do
> >     eval echo "$varname""_lc: \$$varname""_lc"
> > done
> > echo "Escape first, quotes second:"
> > for varname in test1a test1b test1c; do
> >     eval echo "$varname\_lc: \$$varname""_lc"
> > done
> > echo "Quotes first, escapes second:"
> > for varname in test1a test1b test1c; do
> >     eval echo "$varname""_lc: \$$varname\_lc"
> > done
> > echo "Escapes both:"
> > for varname in test1a test1b test1c; do
> >     eval echo "$varname\_lc: \$$varname\_lc"
> > done
>
> Jeff, try using this line where you want to escape the
> second derived variable.  I think this does what you
> want it to.
>
> eval echo "${varname}_lc: \$${varname}_lc"
>
> c
>
>
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