5th day (half day) "Shell programming preliminary, grep and regular Expressions"

Day 5th (half day) "Shell programming preliminary, grep and regular expression" shell programming preliminary (_RECV)

Shell script: Text file

#!:/ Bin/bash

#!:/ Usr/bin/python

#!:/ Usr/bin/perl

Case Listing 1:

Vim first.sh

#!:/ Bin/bash

Cat/etc/fstab

Wc–l/etc/fstab

Give script permissions Chmod a+x first.sh

Run the script./first.sh

------------------------------------------------------------------

Logical operation:

True

False

And:

1 && 1 =1

1 && 0=0

0 && 1 =0

0 && 0 =0

Or:

1 | | 1= 1

1 | | 0= 1

0 | | 1= 1

0 | | 0 =0

Non -:

！ 1 = 0

！ 0 = 1

grep and regular Expressions (_RECV)

The Three musketeers of text processing on Linux:

Grep: Text Filtering tool

Sed: Text Editing tools

Awk:

Grep:global search Regular expression and print out of the line

Function: Text Search tool, according to the user-specified mode of the target text line by row to accompany the check;

Grep:

-V: Reverse lookup, which outputs rows that do not match the lookup criteria

Grep root/etc/passwd

-e: extended regular expression;

-G: basic regular expression;

-F: Fixed string

-I: ignore character case;

-O: Displays only the matched string;

Grep–o root/etc/passwd

-Q: Silent mode, do not enter any information

Grep–q root/etc/passwd

-C: Statistics A total number of lines;

-N: Displays line numbers on the left;

-A number: after # line

-B Number: Front # line

-C Number: Before and after # lines

Grep–c ' Nologin ' passwork

Allisa grep= ' Grep–color=auto '

Grep root/etc/passwd

Basic regular Expression meta-characters:

Character Matching:

.: Matches any single character

Grep ' R.ot '/etc/passwd

[]: matches any single character within the specified range

Grep [Root]/etc/passwd

[^]: matches any single character outside the specified range

Grep [^root]/etc/passwd

[0-9]: Statistics in the specified range of numbers

[:d Igit:], [: Lower:], [: Upper:], [: Alpha:], [: Alnum:], [:p UNCT:], [: Space:]

Grep [0-9]/etc/passwd

Number of matches: used after the number of characters to be specified, to specify the number of occurrences of the preceding character;

*: matches the preceding character any time;

For example: grep "X*y"

. *: Any character of any length;

Location anchoring:

^: Anchor at the beginning of the line for the leftmost mode

$: End of line anchoring,

^$: Empty line;

5th day (half day) "Shell programming preliminary, grep and regular Expressions"