cat concatenates files and prints to standard output
Grammar introduction
cat [OPTION]... [FILE]...
-A --show-all is equivalent to -vET
-b show numbers without blank lines
-n show numbers including blank lines
-E show line terminators
-s continuous multiple Line blank, show line
-T show tab
-v Use ^ and M- symbols, except for LFD and TAB.
scenes to be used:
show line number
[root@localhost ~]# cat -n anaconda-ks.cfg
connection view
[root@localhost ~]# cat -n anaconda-ks.cfg /etc/hosts
Merge files
[root@localhost ~]# cat t1 t2 > t3
Redirect text input
[root@localhost ~]# cat << EOF
hello world
EOF
hello world
Redirect file input
[root@localhost ~]# cat < anaconda-ks.cfg
more
Display files by percentage, with filter, search function, easier to read than cat for large files
parameter:
-num The number of lines displayed at a time
-d Prompt the user to display [Press space to continue, 'q' to quit.] at the bottom of the screen, if the user presses the wrong key, it will display [Press 'h' for instructions.] Instead of 'beep'
-l cancel the function that will pause when encountering a special character ^L (feed character)
-f When calculating the number of lines, use the actual number of lines, not the number of lines after word wrap (some If the number of words in a single line is too long, it will be expanded to two or more lines)
-p does not display each page in a scrolling manner, but first clears the screen and then displays the content
-c is similar to -p, except that it is displayed first Clear other old data after the content
-s When encountering a blank line with more than two consecutive lines, replace it with a blank line
-u Do not display the lower quotation mark (it varies according to the terminal specified by the environment variable TERM)
+/pattern Search for the string (pattern) before each document is displayed, then start to display after the string
+num Display fileNames from line num
The documents to be displayed can be plural
Operation command:
Enter goes down n lines, needs to be defined. The default is 1 line
Ctrl+F Scroll down one screen
Spacebar Scroll down one screen
Ctrl+B Return to the previous screen
= output the line number of the current line
: f output the file name and the line number of the current line
V call the vi editor
! command Call Shell and execute the command
/keyword to search for the keyword
q to exit more
Common operations:
[root@localhost ~]# more -s -20 anaconda-ks.cfg
less
More flexible than more, the mouse can scroll back and forth, browse at will, or lazy load, the parameter usage is similar to more
Common operations:
[root@localhost ~]# less -s -20 anaconda-ks.cfg
head
View the first few lines of the file
[root@localhost ~]# head -2 anaconda-ks.cfg
tail
View the last few lines of the file, as well as the monitoring file function
parameter:
-n show number of lines
-f monitor file
Common operations
[root@localhost ~]# tail -2 anaconda-ks.cfg
[root@localhost ~]# tail -f anaconda-ks.cfg
Based on python to implement tail to view the last few lines of a file
def read_last_lines(filename,lastlines=1):
f = open(filename, 'rb')
first_line_data,first_tell = f.readline(),f.tell()
f.seek(0)
seek = 0
#第一层循环判断是否为空文件
for i in f:
while True:
f.seek(seek,2)
current_tell = f.tell()
seek -= 1
data = f.readlines()
if(first_tell == current_tell and not data):
f.close()
return '1',[first_line_data]
elif(first_tell == current_tell and data):
if(len(data)<lastlines):
data.insert(0,first_line_data)
f.close()
return '2',data
else:
if(lastlines != 1):
if(len(data) == lastlines):
return '3',data
else:
if (len(data) == 1):
if (first_tell == f.tell()):
f.close()
return '4', data[-1:]
if (len(data) > 1):
f.close()
return '5', data[-1:]
data = read_last_lines('test2.txt',lastlines=10)
print(data)To be continued....