Linux.CommanlineTool.grep

grep

1 grep [Options] PATTERN [FILE ...] 2 grep [Options] [-E PATTERN |-F FILE] [FILE ...]

1. grep's regular Expression

REF[1]

A): Match single character

The basic building block in Reg EX is a reg ex that matches a single character. Most characters (including numbers and letters) are matched to their own Reg ex.

B): meta-character

Any metacharacters (metacharacter) that has a special meaning is identified by a leading backslash (backslash, i.e.: \).

C): Bracket expression

Bracket expression is a list of characters surrounded by []. Such expressions match any one of the characters in the list (note that only one character is matched).

If ^ is the first character in a character list, the expression matches any character that is not in the list.

For example: [0123456789] matches any a single number; [A-z] matches any lowercase letter.

To match the character '] ', you need to place '] ' in the first position of the word list characters. Example: []a-z]

A similar to match ' ^ ' needs to place ' ^ ' in the first position of the character list. Example: [a^]

Similar to match '-' need to put '-' in the last position of the character list. Example: [A]

D): Named character category (named classes of characters)

[: Alnum:] [: Alpha:] [: Cntrl:] [:d Igit:] [: Graph:] [: Lower:] [:p rint:] [:p UNCT:] [: Space:] [: Upper:] [: Xdigit:]

E): '. ' Dot matches any single character. \w and [[: Alnum:]] synonymous, \w and [^[:alnum:]] synonymous.

F): ^ and $ match an empty string for the beginning and end of a line, respectively. For example:

$ grep ^line1 Data

Matches the line that begins with "Line1" in the file data.

G): \< \>

The symbols \< and \> respectively match the empty string at the beginning and end of a word.

H): \b \b

The symbol \b matches the empty string at the edge of a word, and \b matches the empty string

Provided it ' s not at the edge of a word.

I): Repeat operator (repetition operator)

Repetition operator

?	The preceding item is optional and matched at most once.
*	The preceding item would be matched zero or more times.
+	The preceding item would be a matched one or more times.
N	The preceding item is matched exactly n times.
{N,}	The preceding item is a matched n or more times.
{N,m}	The preceding item is a matched at least n times, and not more than m times.

J): Match meta-character *

?, +, {, |, (, and) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \ (, and \)

K): Reg EX Operation: concatenation, join

Regular expressions may concatenated; The resulting regular expression matches any string formed

By concatenating, substrings that respectively match the concatenated subexpressions.

Regular expressions is joined by the infix operator |; The resulting regular expression matches

Any string matching either subex-pression.

Repetition takes precedence over concatenation, which on turn takes precedence over alternation.

A whole subexpression is enclosed in parentheses to override these precedence rules.

The backreference \ n, where n is a single digit, matches the substring previously matched by the nth parenthesized

subexpression of the regu-lar expression.

For example: $ grep "Line1\|line2" data

Matches rows that contain "line1" or "line2".

2. grep's example

[Todo]: ref[2]

Reference

1. grep

Http://unixhelp.ed.ac.uk/CGI/man-cgi?grep

2. Advanced Regular Expressions in Grep Command with ten Examples–part II

http://www.thegeekstuff.com/2011/01/advanced-regular-expressions-in-grep-command-with-10-examples-%E2%80%93-part-ii/

Linux.CommanlineTool.grep