Shell (5) Regular Expression .doc

Regular Expression Engine

The special characters that describe the matching mode and the general characters;

 

Bre POSIX
Basic regular expression,
Ere
Extended regular expression;
Gawk
Supported
Ere
,
Sed
Not supported.

 

1)



Regular Expression mode:

L



Case Sensitive

L



Space as common characters

L



The usage mode of a tool or language is
/Pattern/

 

Special characters:
. * [] ^ $ {}/+? | ()

 

Bre
"
/
"

Escape
Escape
Character

Escape is also required for the oblique bearing, although it is not a special character-because
/
Used as expression mode?

 

"
^
", Positioning character, starting from scratch

For example
Sed-n
'/^ ABC/P'
;
^
Must be placed at the beginning of the regular expression; otherwise, it is a common character.

 

"
$
", Positioning character, search for the end

Sed-n'/ABC $/P'
;

Eg:
Search the entire row
, '/^ This $/P'
; Search for empty rows
'/^ $/D ';

 

"
.
"

Match any single character except the line break. It must have one character;

 

"
[]
", Character class

Character class
(One of several characters), such
Sed-n'/[YY] ES/P'

Negative character class, use
[^]
, Such
[^ CH]
, Indicating that it does not contain these characters, but still needs one character;

Define the character range, such
[0-9]
,
[A-Z]
,[
A-cx-z
] Defining multiple ranges

 

Bre
Special character class:

[[: Alpha:]

Any letter, case sensitive

[[: Alnum:]

Any letter, number

[[: Blank:]

Space or tab

[[: Digit:]

Number

[[: Lower:]

Any lower case

[[: Print:]

Any printable

[[: Punct:]

Punctuation Marks

[[: Space:]

Any blank character,
Including vertical tabs,
Such as space,
Lt
,
NL
,
Cr
And so on

[[: Upper:]

Any capital

[[: Cntrl:]
ASCII
Control characters

[[: Graph:]

Non-control non-space

[[: Xdigit:]
16
Hexadecimal number

 

"
*
"

*
The preceding characters may not appear or appear multiple times,
/Colou * r/

"
.*
", A word that appears in any position on a line of text

*
Used for character classes:

Eg:
$ Echo "BT" | sed-n'/B [AC] * t/P'
# TBD

:
AC

Can appear at will?

 

Ere
"
?
"

Same
*
Different: does not appear or only appears once, can also be used with character class

 

"
+
"

Same
*
Must appear once or multiple times

 

"
{}
"

Limit the number of repeated characters
(Interval)
,
{M}
Or
{M, n}
,
/{Min, max /}
,{
M,
} Indicates at least
M
Times

Be {1} t

#

Equivalent
Bet

?

Gawk
Parameters must be specified
-- Re-interval
,

Eg:

Echo
"BT" | gawk -- Re-interval '/be {1} t/{print $0 }'

Used for character classes:

Gawk
-- Re-interval "/B [AE] {1, 2} t"

 

"
|
"

Logic
Or
, Specifying multiple regular expressions,
Gawk '/CAT | dog /'

 

"
()
"

Group, a combination is processed as a standard character,
Eg:

Gawk
'/SAT (urday )? /
#

Requirements
Urday

Appears
0

To
1

Times;

Gawk
'/(C | B) A (B/T )/'
# TBD

: Equivalent
'[CB] a [BT]'?