Sed Regular Expressions
External
Internal
Meta-Characters - Special Characters (need to be escaped in regular expressions)
/ " $ # unescaped signifies end of line ^ # unescaped signifies the beginning of a line ! [ ] : * # zero or more . # dot
Single quote is a special case, to match it use its ASCII hexadecimal value prefixed by \x as follows, instead of escaping it:
\x27
To use () for grouping, they need to be escaped:
\(...\)
More details in Grouping below.
Non-Special Characters (do not need to be escaped in regular expressions)
<
>
(
)
!
-
{
}
+
+ by itself is not a meta-character, it matches "+".
The GNU version matches \+ with "one or more characters"
Grouping
Use \( and \) for grouping. Parentheses must be escaped to be interpreted as grouping separator.
Brackets
Brackets mean "any one of"
[ab]
will match "a" or "b".
echo "blah" | sed -s 's/[ab]/x/g'
prints "xlxh".
Brackets and Negation
Match everything except the specified characters. More than one characters is matched. The behavior is different from the behavior of bash patterns on negation:
[^abc]*
Match Zero or One Character
Normally, this would be achieved with ? placed after the character or the group of characters in questions, but this not work with standard sed.
Examples
Match everything except space:
[^ ]*
.*
seems to work too.
Words (digits, alpha, _):
sed -e 's/[0-9a-zA-Z_]*/THIS_WAS_A_WORD/g'
Blank spaces (spaces, tabs, newlines): \s does not seem to work.
Regular Expression Syntax
TO NORMALIZE across java Regular Expression Syntax, grep Regular Expression Syntax, sed Regular Expression Syntax.