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Distribution: Debian Wheezy/Jessie/Sid, Linux Mint DE
From the man page:
In GNU grep, there is no difference in available functionality between basic and extended syntaxes.
jlinkels@donald-pc:/tmp$ grep -V
GNU grep 2.6.3
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
Now this shows that there apparently is a difference between grep and grep -E. And that is in contradiction with the manual page.
jlinkels@donald-pc:/tmp$ echo aa | grep "a+"
jlinkels@donald-pc:/tmp$ echo aa | grep -E "a+"
For me "+" never worked in grep, but I thought it was my fault. Now I see that it apparently is only evaluated using the extended syntax. However, I can't find any reference to "+" being part of the extended syntax.
Escaping the + symbol is nonsense, it is part are the regular expression, not to be taken as literal character.
grep (GNU grep) 2.14
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This seems to be my grep version .
echo aa | grep 'a\+'
echo aa | grep "a\\+"
echo aa | grep a\\+
All three are working fine . Also i did not understand the part about shell removing my back slash . Please help me in understanding it . Where can i find information on how shell would react to '\' at different places .