Re: bash null conditional

[Robert Nichols <rnicholsNOSPAM comcast net>]

Craig White wrote:
> I'm in my bash book and looking on web but can't seem to resolve this
> simple problem.
>
> $ if [ -n "grep A121 myfile.csv" ]; then echo "null"; fi
> null
>
> $ if [ -n "grep A125 myfile.csv" ]; then echo "null"; fi
> null
>
> A125 definitely is null when I just run the grep command in the quotes
> but A121 definitely is not null.
>
> What am I missing on the if/null operator here?

As written, you are asking if the literal string "grep A121 myfile.csv"
is non-null, which obviously is true and has nothing whatsoever to do
with the 'grep' command, which is never invoked.

$ if [ -n "`grep A121 myfile.csv`" ]; then echo "null"; fi

This will actually invoke 'grep' and insert its output into the string
to be tested.

--
Bob Nichols     "NOSPAM" is really part of my email address.
                Do NOT delete it.