Re: greps pipes and eval bad patterns

[Ray Andrews <rayandrews@eastlink.ca>]

On 10/25/2015 06:17 PM, Kurtis Rader wrote:
> In addition to what Bart said I'll point out that it's usually easier and
> safer to avoid the eval by using an if/else block. Getting the quoting
> right when using eval can be very difficult. Especially if you don't have
> direct control over the text being eval'd; e.g., if some of it is supplied
> by the user; or even just built up from earlier parts of the function.
>
> I have several functions where 99% of the time I want the output
> automatically piped into my pager (e.g., /usr/bin/less). But if the output
> of the function is redirected away from my tty I don't want the pager in
> the pipeline. So instead of using a variable that would normally contain "|
> $PAGER" and sometimes be empty (i.e., using Ray's approach) I simply spell
> it out:
>
>      if [[ -t 1 ]] ; then
>        grep -h -E $case_insensitive -- "$search_for" $files | $PAGER
>      else
>        grep -h -E $case_insensitive -- "$search_for" $files
>      fi

That's exactly the sort of thing I did before in this sort of 
situation.  I take your caveats  seriously tho.  Mostly I was just 
interested in the problem for my education.  I can quite see that eval 
could do some weird stuff if the input was uncertain.  What matters most 
is that the code is clear both to read and to execute. Having a pipe 
inside a variable seems unsound.