How to grep, excluding some patterns?

How about just chaining the greps?

grep -n 'loom' ~/projects/**/trunk/src/**/*.@(h|cpp) | grep -v 'gloom'

Another solution without chaining grep:

egrep '(^|[^g])loom' ~/projects/**/trunk/src/**/*.@(h|cpp)

Between brackets, you exclude the character g before any occurrence of loom, unless loom is the first chars of the line.

A bit old, but oh well...

The most up-voted solution from @houbysoft will not work as that will exclude any line with "gloom" in it, even if it has "loom". According to OP's expectations, we need to include lines with "loom", even if they also have "gloom" in them. This line needs to be in the output "Arty is slooming in a gloomy day.", but this will be excluded by a chained grep like

grep -n 'loom' ~/projects/**/trunk/src/**/*.@(h|cpp) | grep -v 'gloom'

Instead, the egrep regex example of Bentoy13 works better

egrep '(^|[^g])loom' ~/projects/**/trunk/src/**/*.@(h|cpp)

as it will include any line with "loom" in it, regardless of whether or not it has "gloom". On the other hand, if it only has gloom, it will not include it, which is precisely the behaviour OP wants.

Just use awk, it's much simpler than grep in letting you clearly express compound conditions.

If you want to skip lines that contains both loom and gloom:

awk '/loom/ && !/gloom/{ print FILENAME, FNR, $0 }' ~/projects/**/trunk/src/**/*.@(h|cpp)

or if you want to print them:

awk '/(^|[^g])loom/{ print FILENAME, FNR, $0 }' ~/projects/**/trunk/src/**/*.@(h|cpp)

and if the reality is you just want lines where loom appears as a word by itself:

awk '/\<loom\>/{ print FILENAME, FNR, $0 }' ~/projects/**/trunk/src/**/*.@(h|cpp)