That looks like an error in their instructions.
It plainly says:
Quote:
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While grep supports a handful of regular expression commands, it does not support certain useful sequences such as the + and ? operators. If you would like to use these, you will have to use extended grep (egrep). Egrep is equivalent to grep -E, but as it is fairly common to want the extended functionality, egrep is also its own separate command.The Following command illustrates the ?, which matches 1 or 0 occurences of the previous character
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It then goes on to use the non-working example...
Code:
grep "boots?" a_file
... which will only work with the -E option which is not shown, or with egrep.
Try these:
Code:
grep -E "boots?" a_file
egrep "boots?" a_file
