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Re: bash null conditional



Craig White wrote:
On Mon, 2009-03-30 at 13:33 -0500, Justin Willmert wrote:
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?

Craig

Have you tried
    $ if [ -n $(grep A121 myfile.csv) ]; then echo "null"; fi
    $ if [ -n $(grep A125 myfile.csv) ]; then echo "null"; fi

The double quotes make a string, but it looks like you which to be executing grep which is accomplished by using the $() notation. You could also use a pair of backticks surrounding the command.
----
I started with backticks...

$ if [ -n `grep A125 ARdebtorsmaster.csv` ]; then echo "null"; fi
null
$ if [ -n `grep A121 ARdebtorsmaster.csv` ]; then echo "null"; fi
bash: [: too many arguments

which interestingly is also the same problem that I get with your first
suggestion...

$ if [ -n $(grep A125 ARdebtorsmaster.csv) ]; then echo "null"; fi
null
$ if [ -n $(grep A121 ARdebtorsmaster.csv) ]; then echo "null"; fi
bash: [: too many arguments

and then of course, light bulb goes off...I have to figure out how to
get a basic exit code from grep, but seemingly the -s and the -q aren't
the answer.

They are. You want
  if ! grep -q pat file; then echo null; fi
or my personal choich
  grep -q pat file || echo null

--
Bill Davidsen <davidsen tmr com>
  "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot


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