Sed Regular Expressions

External

• https://www.gnu.org/software/sed/manual/html_node/Regular-Expressions.html

Internal

• sed
• Regular Expressions

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.