GNU bug report logs -
#70476
`**` GNU extension only works when ERE syntax is enabled
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bug#70476
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(Fri, 19 Apr 2024 23:06:15 GMT)
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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):
[Message part 1 (text/plain, inline)]
$ sed --version
sed (GNU sed) 4.9
The documentation for sed BRE syntax states:
> As a GNU extension, a postfixed regular expression can also be followed by *; for example, a** is equivalent to a*
https://www.gnu.org/software/sed/manual/sed.html#BRE-syntax
But sed reports an error when ** is used in a BRE expression
$ seq 10 20 | sed 's/1**//'
sed: -e expression #1, char 7: Invalid preceding regular expression
and only allows this syntax when ERE syntax is enabled
$ seq 10 20 | sed -E 's/1**//'
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grep, which also implements this GNU extension, allows ** in BRE syntax
$ seq 10 20 | grep -o '1**'
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$ seq 10 20 | grep -oE '1**'
1
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Additionally, the documentation for the `--posix` flag states
> disable all GNU extensions.
** is specifically documented as a GNU extension, but `--posix` doesn't disable the use of **
$ seq 10 20 | sed --posix -E 's/1**//'
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[Message part 2 (text/html, inline)]
This bug report was last modified 217 days ago.
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Copyright (C) 1999 Darren O. Benham,
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1994-97 Ian Jackson.