Regular Expressions Tables

Reference: Sarwar et al, Unix the textbook, 2nd Edition, Addison-Wesley, 2005, Pp. 248-250

Table 1: Regular Expression Operators and Their Support By Unix Tools

Name/Function Operator Example Usage Meaning Supported By

Alternation | x|y|z x or y or z awk, egrep

Any Character . .com Acom, Bcom, Ccom,
acom, bcom, ccom, ... All

Beginning of Line ^ ^x A line that starts with x
as the first character All

Concatenation xyz x followed by y followed by z All

End of Line $ x$ A line that ends with x
as the last character All

Escape Sequence
Cancels The special meaning
of the next character
following it \ \* An ordinary asterisk * ed, sed, vi, awk, grep

Delimiter: Marks the beginning
or End of a Regular Expression / /L..e/ Love, Lave, Live, Lose, ... ed, sed, vi, awk

Grouping ( ),  (xy)+ xy, xyxy, xyxyxy, ... All

Optional ? xy? 0 or exactly 1 of previous character: x, xy Awk, egrep

Word Anchor \< and \> \<word\> word (not part of a larger substring) All

Repetition * xy* match 0 or more of previous character: x, xy, xyy, xyyy, ... All

Repetition + xy+ match 1 or more of previous character: xy, xyy, xyyy, ... Awk, egrep

Repetition \{m,n\} xy\{6,8\} match at least 6 and no more than 8 of
previous character: xyyyyyy, xyyyyyyy, xyyyyyyyy All

Set
menu of what can match
a single character position [ ] [Hh]ello Hello, hello All

Set
menu of what cannot match
a single character position [^ ] [^A-IK-Z]ello Jello, hello, bello, ... All

Table 2: Examples Of Regular Expressions for vi And Their Meaning

Regular Expression Meaning Examples

/^Yes/ The string Yes At
The Beginning Of The Line Yes...
Yesteryear ...
Yesterday ...

/th/ The string th
Anywhere In The Line the
there
path
bathing

/:$/ A Line Ending With A Colon ... the following:
... below:
... list of:

/[0-9]/ A Single Digit 0 1 2 3 4 5 6 7 8 9

/[a-z] [0-9]/ A Single Lower Case Letter
Followed By A Single Digit a0 b1 c2 d3 e4 f5 w6 x7 y8 z9

/\.c/ An Ordinary Period Character
Followed By A 'c' lab1.c program1.c client.c server.c

/[a-zA-Z ]*/ Any String Containing Zero Or More Of:
Upper And/Or Lower Case Letters
And/Or Spaces Only Any String Without Numbers Nor
Punctuation: e.g. Not 767-!

Table 3: Some Commonly Used vi Commands Which Use Regular Expressions

Command Meaning

/ [0-9] / Do A Forward Search For A Single
Standalone Digit Character (Surrounded By Spaces)
In The Current File; Digits That Are In Substrings
Don't Match

?\.c[1-7] ? Do A Backward Search For Words Or
Strings In Words That End In .c Followed By
A Single Digit Between 1 And 7 Inclusive

:1,$s/:$/./ Search The Whole File And Substitute
A Period Whenever A Colon At The End Of The Line Is Found

:.,$s/^[Hh]ello /Greetings / Search From The Current Line To the End Of The File
For Hello Or hello At The Beginning Of The Line And Replace Either
With Greetings

:1,$s/^ *// Search The Entire File For Any Leading Spaces At The
Beginning Of All Lines And Delete Them

Name/Function	Operator	Example Usage	Meaning	Supported By
Alternation	\|	x\|y\|z	x or y or z	awk, egrep
Any Character	.	.com	Acom, Bcom, Ccom, acom, bcom, ccom, ...	All
Beginning of Line	^	^x	A line that starts with x as the first character	All
Concatenation		xyz	x followed by y followed by z	All
End of Line	$	x$	A line that ends with x as the last character	All
Escape Sequence Cancels The special meaning of the next character following it	\	\*	An ordinary asterisk *	ed, sed, vi, awk, grep
Delimiter: Marks the beginning or End of a Regular Expression	/	/L..e/	Love, Lave, Live, Lose, ...	ed, sed, vi, awk
Grouping	( ), \( \)	(xy)+	xy, xyxy, xyxyxy, ...	All
Optional	?	xy?	0 or exactly 1 of previous character: x, xy	Awk, egrep
Word Anchor	\< and \>	\<word\>	word (not part of a larger substring)	All
Repetition	*	xy*	match 0 or more of previous character: x, xy, xyy, xyyy, ...	All
Repetition	+	xy+	match 1 or more of previous character: xy, xyy, xyyy, ...	Awk, egrep
Repetition	\{m,n\}	xy\{6,8\}	match at least 6 and no more than 8 of previous character: xyyyyyy, xyyyyyyy, xyyyyyyyy	All
Set menu of what can match a single character position	[ ]	[Hh]ello	Hello, hello	All
Set menu of what cannot match a single character position	[^ ]	[^A-IK-Z]ello	Jello, hello, bello, ...	All

Regular Expression	Meaning	Examples
/^Yes/	The string Yes At The Beginning Of The Line	Yes... Yesteryear ... Yesterday ...
/th/	The string th Anywhere In The Line	the there path bathing
/:$/	A Line Ending With A Colon	... the following: ... below: ... list of:
/[0-9]/	A Single Digit	0 1 2 3 4 5 6 7 8 9
/[a-z] [0-9]/	A Single Lower Case Letter Followed By A Single Digit	a0 b1 c2 d3 e4 f5 w6 x7 y8 z9
/\.c/	An Ordinary Period Character Followed By A 'c'	lab1.c program1.c client.c server.c
*/[a-zA-Z ]/**	Any String Containing Zero Or More Of: Upper And/Or Lower Case Letters And/Or Spaces Only	Any String Without Numbers Nor Punctuation: e.g. Not 767-!

Command	Meaning
/ [0-9] /	Do A Forward Search For A Single Standalone Digit Character (Surrounded By Spaces) In The Current File; Digits That Are In Substrings Don't Match
?\.c[1-7] ?	Do A Backward Search For Words Or Strings In Words That End In .c Followed By A Single Digit Between 1 And 7 Inclusive
:1,$s/:$/./	Search The Whole File And Substitute A Period Whenever A Colon At The End Of The Line Is Found
:.,$s/^[Hh]ello /Greetings /	Search From The Current Line To the End Of The File For Hello Or hello At The Beginning Of The Line And Replace Either With Greetings
*:1,$s/^ //**	Search The Entire File For Any Leading Spaces At The Beginning Of All Lines And Delete Them