Platform Support for GNU Extensions to Basic Regular Expressions (opens in new tab)

Recently I was reviewing some shell script a colleague had written: if grep -e '@[^@]\+@' "$DIR/install.sh" ; then I thought the \ before the + was a mistake, and also pointed out that if + was to be used we’d probably need to pass -E for extended regular expression (ERE) support. The colleague replied that \+ in a basic regular expression (BRE) was the same as + in ERE (one or more repetitions). This was news to me! I wanted to know more, so I turned to the FreeBSD \+ did in fact work. Meanw...