grep with regular expression:
1, grep program
There trio --grep sed awk text processing under linux
grep: text line filtering tools
sed: text line editor (stream editor)
awk: report generator (do formatting text output)
grep: contains three commands: grep egrep fgrep, they are used for pattern matching row
egrep = gerp -E // use extended regular expression matching
fgrep = fast grep // use files matching the wildcard
* Grep default use regular expressions to match text
grep usage:
grep 【option】 ... PATTERN【filename】
grep common options --option
-E support the use of extended regular expressions
-P use perl regular expression language search engine (each language regex engine is not the same)
-i ignore case
-w word match fixing
-v Invert Selection
-o output only matched content
--color = auto syntax coloring
-n Display line numbers
PATTERN-- regular expressions
Role: through some special characters to represent a class character, and then to the front of the command to execute; if you use special characters meaning in itself, it is necessary \ to escape
1, character match
The representative of any one character corresponds to file a wildcard?
[] Any one of the characters in the range
Any one character [^] outside the range
Character classes: [: digit:]
Any number, equivalent to 0-9
[: Lower]
any lowercase letter
[upper:]
any capital letters
[alpha:]
any case letters
[: alnum:]
any number or letter
[: blank :] |
horizontal whitespace
[: space:]
horizontal or vertical whitespace
[punct:]
punctuation
[Print:]
Printable characters
[: cntrl:]
the control (non-printing) characters
[: graph:]
graphic characters
[xdigit:]
hexadecimal characters
2, matching the number of times *** match whitespace characters ^ [[: space:]] ***
* Matches the preceding character zero to many times
\? Matches the preceding character zero to 1
+ One character matches one thousand meters lesson plans to the n-th
\ {M \} characters arranged in front of M times
\ {M, n \} matches the character preceding to n times m
\ {0, n \} matches the preceding character zero to n times
\ {M, \} the preceding matching character least m
3, the position of the anchor
^ Anchor of the line
$ Anchored end of the line
\ B anchor and anchor the first word endings
\> Anchor suffix
\ <Anchoring the first word
4, group
\ (\) Example: \ (abc \) * abcabc
Grouping characteristics: By default, Linux system will be designated as the grouping variable, variable representation of \ 1 \ 2 \ 3 .....
Important points: interactive mass participation: read -p # // - t is wait a few seconds
Examples: read -p ( "Please enter a thing:") filename