[SOLVED] not sure what's the problem with this "regex" in the "grep" shell command

Issue

This was my attempt:

grep -i 'th[\D]\{1,\}'

I'm on hackerRank. I have this file that is delivered to my stdin.

I need as a result lines that contains :

the
that
then
those

Solution

In a POSIX BRE pattern, when you use a "shorthand character class" like \s, \w, even in GNU grep, these escape sequences are treated as separate chars, a backslash and a letter. [\D]\{1,\} matches one or more D letters or \ chars.

You need to match exactly the words you are told to:

grep -i -E '\<(the|that|then|those)\>'

Here,

• -i - enables case insensitive matching
• -E - enables POSIX ERE syntax
• \< - open word boundary
• (the|that|then|those) - s capturing group matching any of the word in between | (OR) alternation operators
• \> - close word boundary.

Answered By - Wiktor Stribiżew