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Since the grep in this environment doesn't support Perl-style regular expressions, you can't use "\d". If you use Basic Regular Expressions (the default and equivalent to --basic-regexp or -G), you can use the character class [0-9] (see https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html).
In BRE, the capture group must be defined in a subexpression with \( \) and then can be recalled with \1 (see https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions). Finally, BRE doesn't support using the precise '?' matching operator to pick out the optional space, but it does permit the more greedy '*'. So you end up with:
grep '\([0-9]\)\s*\1'
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'Grep' - B
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Since the
grepin this environment doesn't support Perl-style regular expressions, you can't use "\d". If you use Basic Regular Expressions (the default and equivalent to--basic-regexpor-G), you can use the character class[0-9](see https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html).In BRE, the capture group must be defined in a subexpression with
\( \)and then can be recalled with\1(see https://en.wikibooks.org/wiki/Regular_Expressions/POSIX_Basic_Regular_Expressions). Finally, BRE doesn't support using the precise '?' matching operator to pick out the optional space, but it does permit the more greedy '*'. So you end up with:grep '\([0-9]\)\s*\1'