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Regular Expressions are a widely-used method of specifying patterns of text to
search for. Special metacharacters allow you to specify, for instance, that a particu-
lar string you are looking for, occurs at the beginning, or end of a line, or contains n
recurrences of a certain character. 

Any single character matches itself, unless it is a metacharacter with a special
meaning described below. A series of characters matches that series of characters
in the target string, so the pattern 

"short"

would match 

"short"

in the target string.

You can cause characters that normally function as metacharacters or escape
sequences to be interpreted by preceding them with a backslash 

"\"

. 

For instance, metacharacter 

"^"

matches beginning of string, but 

"\^"

matches

character 

"^"

, and 

"\\"

matches 

"\"

, etc. 

unsigned 

matches

string 'unsigned' 

\^unsigned 

matches

string '^unsigned' 

Characters may be specified using a escape sequences: 

"\n"

matches a newline,

"\t"

a tab, etc. More generally, 

\xnn

, where nn is a string of hexadecimal digits,

matches the character whose ASCII value is 

nn

. 

If you need wide (Unicode) character code, you can use 

'\x{nnnn}'

, where 'nnnn'

- one or more hexadecimal digits.

- 

\xnn

- char with hex code nn 

- 

\x{nnnn)

- char with hex code 

nnnn

(one byte for plain text and two bytes

for Unicode) 

- 

\t

- tab (HT/TAB), same as 

\x09 

- 

\n

- newline (NL), same as 

\x0a 

- 

\r

- car.return (CR), same as \x0d 

- 

\f

- form feed (FF), same as 

\x0c 

- 

\a

- alarm (bell) (BEL), same as 

\x07 

- 

\e

- escape (ESC) , same as 

\x1b 

unsigned\x20int 

matches

'unsigned int' 

(note space in the middle) 

\tunsigned 

matches

'unsigned'

(predecessed by tab) 

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- SOFTWARE AND HARDWARE SOLUTIONS FOR EMBEDDED WORLD

CHAPTER 2