4.5. egrep (Extended grep)

The main advantage of using egrep is that additional regular expression metacharacters (see Table 4.4) have been added to the set provided by grep. The \( \) and \{ \}, however, are not allowed. (See GNU grep –E if using Linux.)

Table 4.4. egrep's Regular Expression Metacharacters

Metacharacter	Function	Example	What It Matches
^	Beginning-of-line anchor	'^love'	Matches all lines beginning with love.
$	End-of-line anchor	'love$'	Matches all lines ending with love.
.	Matches one character	'l..e'	Matches lines containing an l, followed by two characters, followed by an e.
*	Matches zero or more of the characters preceding the asterisk	' *love'	Matches lines with zero or more spaces followed by the pattern love.
[ ]	Matches one character in the set	'[Ll]ove'	Matches lines containing love or Love.
[^ ]	Matches one character not in the set	'[^A–KM–Z]ove'	Matches lines not containing A through K or M through Z, followed by ove.
New with egrep
+	Matches one or more of the characters preceding the + sign	'[a–z]+ove'	Matches one or more lowercase letters, followed by ove. Would find move, approve, love, behoove, etc.
?	Matches zero or one of the preceding characters	'lo?ve'	Matches for an l followed by either one or not any occurrences of the letter o. Would find love or lve.
a|b	Matches either a or b	'love|hate'	Matches for either expression, love or hate.
( )	Groups characters	'love(able|ly)' '(ov)+'	Matches for lovable or lovely. Matches for one or more occurrences of ov.

4.5.1 egrep Examples

The following examples illustrate only the way the new extended set of regular expression metacharacters is used with egrep. The grep examples presented earlier illustrate the use of the standard metacharacters, which behave the same way with egrep. Egrep also uses the same options at the command line as grep.

The following datafile is used in the examples in this section.

% cat datafile
northwest	NW	Charles Main	3.0	.98	3	34
western	WE	Sharon Gray	5.3	.97	5	23
southwest	SW	Lewis Dalsass	2.7	.8	2	18
southern	SO	Suan Chin	5.1	.95	4	15
southeast	SE	Patricia Hemenway	4.0	.7	4	17
eastern	EA	TB Savage	4.4	.84	5	20
northeast	NE	AM Main Jr.	5.1	.94	3	13
north	NO	Margot Weber	4.5	.89	5	9
central	CT	Ann Stephens	5.7	.94	5	13

Example 4.30.

% egrep 'NW|EA' datafile

northwest            NW       Charles Main             3.0   .98     3    34

eastern              EA       TB Savage                4.4   .84     5    20

EXPLANATION

Prints the line if it contains either the expression NW or the expression EA.

Example 4.31.

% egrep '3+' datafile

northwest          NW       Charles Main             3.0   .98     3    34

western            WE       Sharon Gray              5.3   .97     5    23

northeast          NE       AM Main Jr.              5.1   .94     3    13

central            CT       Ann Stephens             5.7   .94     5    13

EXPLANATION

Prints all lines containing one or more occurrences of the number 3; e.g., 3, 33, 33333333.

Example 4.32.

% egrep '2\.?[0–9]' datafile

western                WE        Sharon Gray              5.3   .97     5    23

southwest              SW        Lewis Dalsass            2.7   .8      2    18

eastern                EA        TB Savage                4.4   .84     5    20

EXPLANATION

Prints all lines containing a 2, followed by one period or no period at all, followed by a number; e.g., matches 2.5, 25, 29, 2.3, etc.

Example 4.33.

% egrep '(no)+' datafile

northwest          NW       Charles Main             3.0   .98     3    34

northeast          NE       AM Main Jr.              5.1   .94     3    13

north              NO       Margot Weber             4.5   .89     5     9

EXPLANATION

Prints lines containing one or more consecutive occurrences of the pattern group no; e.g., no, nono, nononononono, etc.

Example 4.34.

% egrep 'S(h|u)' datafile

western               WE       Sharon Gray            5.3   .97    5    23

southern              SO       Suan Chin              5.1   .95    4    15

EXPLANATION

Prints all lines containing S, followed by either h or u; e.g., Sharon or Suan.

Example 4.35.

% egrep 'Sh|u' datafile

western               WE       Sharon Gray            5.3   .97    5    23

southern              SO       Suan Chin              5.1   .95    4    15

southwest             SW       Lewis Dalsass          2.7   .8     2    18

southeast             SE       Patricia Hemenway      4.0   .7     4    17

EXPLANATION

Prints all lines containing the expression Sh or u; e.g., Sharon or southern.

4.5.2 egrep Review

Table 4.5 contains examples of egrep commands and what they do.

Table 4.5. Review of egrep

Command	What It Does
egrep '^ +' file	Prints lines beginning with one or more spaces.
egrep '^ *' file	Prints lines beginning with zero or more spaces.[a]
egrep '(Tom|Dan) Savage' file	Prints lines containing Tom Savage or Dan Savage.
egrep '(ab)+' file	Prints lines with one or more occurrences of ab.
egrep '^X[0–9]?' file	Prints lines beginning with X followed by zero or one single digit.
egrep 'fun\.$' *	Prints lines ending in fun. from all files.[a]
egrep '[A–Z]+' file	Prints lines containing one or more capital letters.
egrep '[0–9]' file	Prints lines containing a number.[a]
egrep '[A–Z]...[0–9]' file	Prints lines containing five-character patterns starting with a capital letter, followed by three of any character, and ending with a number.[a]
egrep '[tT]est' files	Prints lines with Test and/or test.[a]
egrep '(Susan|Jean) Doe' file	Prints lines containing Susan Doe or Jean Doe.
egrep –v 'Mary' file	Prints all lines not containing Mary.[a]
egrep –i 'sam' file	Prints all lines containing sam, regardless of case (e.g., SAM, sam, SaM, sAm).[a]
egrep –l 'Dear Boss' *	Lists all filenames containing Dear Boss.[a]
egrep –n 'Tom' file	Precedes matching lines with line numbers.[a]
egrep –s "$name" file	Expands variable name, finds it, but prints nothing. Can be used to check the exit status of egrep.[a] (s stands for silent)

^[a] egrep and grep handle this pattern in the same way.