\b \? \+ \| are GNU extensions to sed
In BRE (Basic Regular Expressions) there is no \? \+ or \|
In ERE (Extended Regular Expressions) there is ? + and |
To specify sed to use ERE, specify the -E flag.
GNU grep does not distinguish between BRE and ERE, but other
implementations do. To make grep use ERE instead of BRE, specify
the -E flag.
The GNU extension \b has no equivalent in either BRE or ERE.
So, in line number 216, I used the whole initial expected output.
For quick reference (n/a means 'not available') -
GNU BRE | POSIX BRE | POSIX ERE
-------------------------------
\( | \( | (
\) | \) | )
\? | \{0,1\} | ? or {0,1}
\+ | \{1,\} | + or {1,}
\| | n/a | |
\b | n/a | n/a
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