Many options with
grep alone, starting with the standard ones:
grep -i -e abc -e uyx
grep -i 'abc
grep -i -E 'abc|uyx'
grep implementations, you can also do:
grep -i -P 'abc|uyx' # perl-like regexps, sometimes also with
# --perl-regexp or -X perl
grep -i -X 'abc|uyx' # augmented regexps (with ast-open grep) also with
grep -i -K 'abc|uyx' # ksh regexps (with ast-open grep) also with
grep -i 'abc\|uyx' # with the \| extension to basic regexps supported by
# some grep implementations. BREs are the
# default but with some grep implementations, you
# can make it explicit with -G, --basic-regexp or
# -X basic
You can add
\(...\) for BREs), but that's not necessary. The
| also need to be quoted for them to be passed literally to
grep as they are special characters in the syntax of the shell language.
Case insensitive matching can also be enabled as part of the regexp syntax with some
grep implementations (not standardly).
grep -P '(?i)abc|uyx' # wherever -P / --perl-regexp / -X perl is supported
grep -K '~(i)abc|uyx' # ast-open grep only
grep -E '(?i)abc|uyx' # ast-open grep only
grep '\(?i\)abc|uyx' # ast-open grep only which makes it non-POSIX-compliant
Those don't really bring much advantage over the standard
-i option. Where it could be more interesting would be for instance if you want
abc matching to be case sensitive and
uyx not, which you could do with:
grep -P 'abc|(?i)uyx'
grep -P 'abc|(?i:uyx)'
(and equivalent variants with other regexp syntaxes).
The standard equivalent of that would look like:
grep -e abc -e '[uU][yY][xX]'
(bearing in mind that case-insensitive matching is often locale-dependent; for instance, whether uppercase
İ may depend on the locale according to
grep -i i).