Description of Linux regular expressions and extended expressions, egrep commands (August 27 job exercise)

1. Summarize the use of the commands involved in this course and show the relevant examples;

Rights Management:
Rights Management: chmod
Affiliation Management: Chown, CHGRP
File Matte Code: Umask

Modify file Permissions: chmod
chmod [OPTION] ... Mode[,mode] ... FILE ...
chmod [OPTION] ... Octal-mode FILE ...
chmod [OPTION] ...--reference=rfile FILE:

Three categories:
U:owner
G:group
O:other
A:all

Two ways to use:
=mode
=rx, =r, =
Ug=rx, go=
[+|-]mode
U+r,
+w
+x

-r:recursive

Modified file owner: Chown
chown [OPTION] ... [OWNER] [: [GROUP]] FILE ...
chown [OPTION] ...--reference=rfile FILE ...
-r:recursive

Modified file group: CHGRP

Umask: Masking Code
Catalog: 777-umask
Files: 666-umask
If the permissions of a certain class of users have permission to execute, it will automatically add 1 to its permission bit.

Umask umask
Set: Valid only for the current shell process;

2. Summarize basic regular expressions and extended regular expressions

Grep:
Linux Text Processing Three musketeers:
grep: Text filtering tool;
Sed: Text editor (line); stream editor
awk: Text report Generator; awk implementation on Linux is gawk

Grep:global search REgular expression and Print out of the line.
Function: Text Search tool, according to user-specified "pattern" line to search for target text, print the matching line;
Pattern: The filter condition written by metacharacters and text characters of regular expressions;

Metacharacters: A character does not represent its literal meaning, but is used to denote a wildcard or control function;

Divided into two categories:
Basic Regular Expressions: BRE
Extended Regular expression: ERE

The regular expression engine;

grep [OPTIONS] PATTERN [FILE ...] ：
Options:
--color=auto: The matching to the string to do highlighting;
-V: The display mode does not match the row;
-I: ignore character case;
-O: Displays only strings that can be matched to the pattern;
-Q: Silent mode;
-E: Using extended regular expressions;

The metacharacters of the basic regular expression:
Character Matching:
. : matches any single character;
[]: matches any single character within the specified range;
[^]: matches any single character outside the specified range;

Character Set:

POSIX Character Set Collection	Description
[: Alnum:]	Any one letter or number (A-Z, A-Z, 0-9)
[: Alpha:]	Any one letter (A-Z, A-Z)
[: ASCII:]	Any one ASCII range character (\x00–\x7f)
[: Cntrl:]	Any one control character (\x00–\x1f, \x7f)
[:d Igit:]	Any one number (0–9)
[:p rint:]	Any one of the ASCII characters that can be displayed (\x20–\x7e)
[: Space:]	Any one whitespace character (\x09–\x0d, \x20)
[: Graph:]	Any one of the ASCII characters that can be displayed, without spaces (\x21–\x7e)
[: Lower:]	Any one lowercase letter (a–z)
[: Upper:]	Any one capital letter (a–z)
[:p UNCT:]	can display the character [:p rint:] to remove the alphanumeric [: alnum:]
[: Xdigit:]	Any one hexadecimal digit (0-9, a-f, a-f)
[: Blank:]	Spaces or tabs (\x20, \x09)
Description	When [: is followed by ^ , the character that represents the corresponding character set is not matched.

Number of occurrences: used to specify the number of times after the character;
*: any time;
Abxy
Xay
Xxxxxxxy

grep "X*y"

\?:0 or 1 times;
grep "X\?y"

\+:1 or multiple times;
\{m\}: Precisely limited to M times;
\{m,n\}: At least m times, up to n times, [M,n]
\{0,n\}: Up to n times;
\{m,\}: at least m times;

. *: Matches any character of any length;

Location anchoring:
^: Anchor at the beginning of the line, for the leftmost mode;
$: End of line anchoring; for the rightmost side of the pattern;
\< \b: The first anchor of the word; the left side of the pattern used to denote the word;
\> \b: the ending anchor; the right side of the pattern used to represent the word;
^$: blank line;

Group: \ (\)

The contents of the pattern in the grouped parentheses are recorded by the regular expression engine during execution, and the built-in variables are saved: The variables are \1, \2, ...
\1: From the left, the first opening parenthesis, and the matching right parenthesis in the middle of the pattern match to the content;
\2:
...

Back reference: Use a variable to refer to the character that matches the pattern in the preceding grouping brackets;

An extended regular expression:
The grep family has three commands:
grep: basic Regular expression
-e: extending regular expressions
-F: Regular expressions are not supported
Egrep: Extending Regular expressions
Fgrep: Regular expressions are not supported

Extend the metacharacters of regular expressions:

differs from the basic regular expression:

Number of matches:
*
?: 0 or 1 times;
+: more than 1 times;
{m}: exact match m times;
{M,n}: At least m times, up to n times;

Group: ()
Back reference: \1, \2, ...

Or:
A|b
C|cat: does not represent cat or cat, but is C or cat;
To be written (C|c) at

3. Display the lines in the/etc/passwd file that end with bash

[[email protected] ~]# grep ' \ (bash\) $ '/etc/passwd

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m01/72/56/wkiom1xhjrar2muhaae_djho51c425.jpg "width=" 642 "height=" 216 "/>

4. Display the two-digit or three-digit number in the/etc/passwd file

[[email protected] ~]# grep ' \b[0-9]\{2,3\}\b '/etc/passwd

Or

[Email protected] ~]# grep-e ' \b[0-9]{2,3}\b '/etc/passwd

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m02/72/56/wkiom1xhjruydb4eaakzai6auke414.jpg "width=" 726 "height=" 376 "/>

Attention:

[[email protected] ~]# grep ' [0-9]\{2,3\} '/etc/passwd wrong wording

5. Display lines with ' LISTEN ' followed by 0, one or more whitespace characters in the ' Netstat-tan ' command result

[Email protected] ~]# Netstat-tan | grep ' Listen[[:space:]] *$ '

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m00/72/53/wkiol1xhmmhiyghraaeonb9dces528.jpg "width=" 833 "height=" 290 "/>

6. Add user bash, Testbash, basher, and Nologin user (Nologin user's shell is/sbin/nologin), then find the same line in the/etc/passwd file as the user name and its shell name

[Email protected] ~]# egrep ' (\b[a-z]+[a-z]\b). *\1$ '/etc/passwd

Description: * Previous matches 0 or n times, \1 references the first \ (\) in front of the $ to what end

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m01/72/53/wkiol1xhmmlhqsa3aafek2ox718828.jpg "width=" 925 "height=" 261 "/>

7. Display the default shell and UID of root, CentOS, or User1 user on the current system (please create these users beforehand, if not present)

[[email protected] ~]# egrep ' ^ (root|centos|user1) '/etc/passwd | Cut-d:-f3,7

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m02/72/53/wkiol1xhmmswagffaacl8tgu98u098.jpg "width=" 943 "height=" 215 "/>

8, find a word in the/etc/rc.d/init.d/functions file (the middle of the word can be underlined) followed by a set of parentheses line

[[email protected] ~]# egrep ' ^ (\w+) \ (. *\) '/etc/rc.d/init.d/functions//This effect is immediately followed by a word ()

[[email protected] ~]# egrep ' ^\w+.*\ (. *\) '/etc/rc.d/init.d/functions//This effect is not followed by a word (), but there is (), and does not end with ()

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m00/72/53/wkiol1xhmmahgocqaaefjod_ric748.jpg "width=" 966 "height=" 385 "/>

9, use echo to output a path, and then egrep find its path base name; Further use Egrep to remove its directory name

Path base Name
[Email protected] ~]# echo "/etc/sysconfig/modules/" | Egrep ' [^/]+/$ '

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m01/72/53/wkiol1xhmmez0qzraab-bqzj1k0740.jpg "width=" 687 "height=" 165 "/>

Directory Name
[Email protected] ~]# echo "/etc/sysconfig/modules" | Egrep--color=auto ' (^[/].*[/]\b) '

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m02/72/53/wkiol1xhmmijso7waab36ued1ey006.jpg "width=" 682 "height=" 158 "/>

Description

[Email protected] ~]# basename/etc/sysconfig/modules/
Modules
[Email protected] ~]# dirname/etc/sysconfig/modules/
/etc/sysconfig
[Email protected] ~]#

10. Find the number between 1-255 in the result of ifconfig command execution

[Email protected] ~]# Ifconfig | Egrep-n ' \b[1-9]\b|\b[1-9][0-9]\b|\b[1-2][0-9][0-5]\b|\b[1][0-9][0-9] '

Effect:

650) this.width=650; "title=" image "style=" border-right-width:0px;background-image:none;border-bottom-width:0px; padding-top:0px;padding-left:0px;padding-right:0px;border-top-width:0px; "border=" 0 "alt=" image "src=" http:// S3.51cto.com/wyfs02/m01/72/53/wkiol1xhmm2jjhr7aaiwj0ktpn8676.jpg "width=" "height=" 297 "/>

Description of Linux regular expressions and extended expressions, egrep commands (August 27 job exercise)