Linux sed detailed

Text Processing Three musketeers:
grep, Egrep, Fgrep: Text filter
Sed:stream Editor, stream editor, line
awk: Text formatting tool, Report Builder

Sed is an online editor that processes a single line of content at a time. When processing, the currently processed rows are stored in a temporary buffer called pattern space, followed by the SED command to process the contents of the buffer, and after processing is done, the contents of the buffer are sent to the screen. Then the next line is processed, so it repeats until the end of the file.

SED command format

sed [OPTION] ... ' Script ' [Input-file] ...
Script: Address delimitation Edit Command

Common options (option):
-N: does not output the contents of the mode space to the screen;
-e script,--expression=script: multi-point editing;
-f/path/to/sed_script_file
One edit command per line;
-R,--regexp-extended: supports the use of extended regular expressions;
-i[suffix],--in-place[=suffix]: Directly edit the original file;
~]# sed-e ' [email protected]^#[[:space:]]*@@ '-e '/^uuid/d '/etc/fstab

Address delimitation (script):
(1) Empty address: To deal with the full text;
(2) Single address:
#: Specify line;
/pattern/: Each row that is matched by this pattern;
(3) Address range
#,#：
#,+#:
#,/pat1/
/pat1/,/pat2/
$: last line;
(4) Step forward: ~
: All Odd lines
2~2: All even lines

Edit command:
D: Delete;
P: Displays the contents of the mode space;
A \text: Append the text "text" After the line, support using \ n to implement multi-row append;
I \text: Insert text "text" in front of line, support using \ n to implement multiline insertion;
C \text: Replace the matched line with the text "text" specified here;
W/path/to/somefile: Saves the line of pattern space to the specified file;
R/path/from/somefile: Reads the contents of the specified file to the current file by the pattern to match the line, file merge;
=: Prints the line number for the line to which the pattern matches;
!: conditional inversion;
Address delimitation! Edit command;
s/*/*/*: Find replacement, its delimiter can be self-specified, commonly used have [email protected]@@, s## #等;
Replace tag:
G: global substitution;
W/path/to/somefile: Saves the result of the substitution success to the specified file;
P: Shows the successful replacement line;

example : (/etc/fstab file cp to/tmp/fstab)

Delete a row

[Email protected] ~]# sed ' 1d '/tmp/fstab #删除第一行

[Email protected] ~]# sed ' $d '/tmp/fstab #删除最后一行

[Email protected] ~]# sed ' 1,2d '/tmp/fstab #删除第一行到第二行

[Email protected] ~]# sed '/boot/d '/etc/fstab #删除包含boot字符串的行

Show a row

[Email protected] ~]# sed-n ' 6p '/tmp/fstab #显示第6行

Here to add the-n option, otherwise the contents of the schema space is the entire contents of the file, the default will be output.

[Email protected] ~]# sed-n ' 2, $p '/tmp/fstab #显示第二行到最后一行

Querying using a pattern

[[email protected] ~]# sed-n '/^#/p '/tmp/fstab #查询以 # start the line and output

Text Insert, replace

Text insertion

[[Email protected] ~]# sed '/^#/a \this test '/tmp/fstab

A \text: Append the text "text" After the line, support using \ n to implement multi-row append;

[[Email protected] ~]# sed '/^#/i \this test '/tmp/fstab

I \text: Insert text "text" in front of line, support using \ n to implement multiline insertion

Line substitution

[[Email protected] ~]# sed '/^#/c\* '/tmp/fstab

replace lines that begin with # with *

[Email protected] ~]# sed-n '/^#/w/tmp/sed.txt '/tmp/fstab

saves the pattern space that matches the line to the specified file. Save lines beginning with # to/tmp/sed.txt

File merge ( reads the contents of the specified file to the line after the current file is matched to the pattern )

[Email protected] ~]# sed '/^#/r./abc.txt '/tmp/fstab

Add the contents of the abc.txt file after the lines that begin with the # number

Print line numbers for lines to which the pattern matches

[[Email protected] ~]# sed '/^#/= '/tmp/fstab

Text Find and replace

[[Email protected] ~]# sed ' [email protected]#@*@g '/tmp/fstab

Replace # with *. Text string substitution

[[Email protected] ~]# sed ' [email protected]#@*@w abc.txt '/tmp/fstab

writes lines that match the replacement criteria to the text

[Email protected] ~]# sed ' [email protected]@[email protected] '/tmp/fstab

To replace the UUID with a UUID

Exercise 1: Remove all white-space characters from the beginning of all lines in the/boot/grub/grub2.cfg file that begin with a blank character;

[[Email protected] ~] #sed ' [email protected]^[[:space:]]\[email protected]@ '/etc/grub2.cfg

Exercise 2: Remove all white-space characters from the beginning of the line at the beginning of the lines in the/etc/fstab file, preceded by #, and #;

[[Email protected] ~]# sed ' [email protected]^#[[:space:]]*@@ '/etc/fstab

Exercise 3: Output an absolute path to the SED command and take out its directory, which behaves like dirname;

[Email protected] ~]# echo "/var/log/messages/" | Sed ' [email protected][^/]\+/\[email protected]@ ' [[email protected] ~]# echo '/var/log/messages ' | Sed-r ' [Email protected][^/]+/[email protected]@ '

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Linux sed detailed