Question

If I do:

if grep someexpression somefile >/dev/null; then
   ...
fi

Things work fine.

To do a “not”, I know I can do this (using [] which is the test command):

if [ '!' somecondition ] ; then
   ...
fi

A simple workaround:

grep someexpression somefile >/dev/null
if [ '!' $? ]; then
   ...
fi

But the above workaround won’t work with a while loop, so then I need to write a function instead, which is annoying. How do I do a not with the grep thing above, the proper way?

Answer 1

Try:

if ! grep someexpression somefile >/dev/null; then
   ...
fi

Note that the space after ! is mandatory, otherwise it will (try to) invoke history expansion.