6.2 bash programming Integer testing and Special variables

6.2 The three great Linux tools.

grep,sed(stream editor), awk

sed basic usage

sed ：Stream EDitor

Line Editor (Full Screen Editor: vi)

sed: pattern space

By default, the original file is not edited, only the data in the pattern space is processed: then, processing

When finished, print pattern space to screen

sed [options] 'AddressCommand' file ...

-n: Silent mode, no longer the default display mode space content

Address:

1 StartLine,EndLine

For example 1, 100 (lines 1 to 100)

$: Last line

2 /REGEXP/

For example/^root/

sed '/oot/d' /etc/fstab

3 /Pattern1/,/Pattern2/

Indicates the beginning of the row first matched by Pattern1, to the first matched by Pattern2

Match to the end of the row, all the rows in between

4 LineNumber

the specified row

sed '1d' /etc/fstab

5 StartLine,+N

Starting from StartLine, N lines backward, N+1 lines in total

sed '1,+2d' /etc/fstab

Command:

d: Delete eligible rows

p: Display eligible rows

a \string: appends a new line after the specified line with the content "string"

\n: Can be used for newlines

i \string: appends a new line with the content "string" before the specified line

r FILE: Adds the contents of the specified file to the qualifying line

w FILE: Save lines in the specified range of addresses as specified files

s/pattern/string/modifier: find and replace (default only replaces the first time in each line

String matched by pattern)

modifier

g: Global substitution

i: ignore case

sed '1,2d' /etc/fstab

sed '/^\//d' /etc/fstab

sed '/^\//a \# hello world' /etc/fstab

sed '/^\//a \# hello world\n # hello,linux' /etc/fstab

sed '2r /etc/issue' /etc/fstab

sed '/oot/w /tmp/oot.txt' /etc/fstab

sed 's/oot/OOT/' /etc/fstab

sed 's/^\//#/' /etc/fstab