Tips for viewing text in Linux (super practical!)

Preface

In daily development, we often need to perform various text and log viewing operations on the server. This article mainly summarizes and summarizes the commonly used text and log viewing skills, so that you can collect them for later viewing and use:

tail command to view log information

Real-time monitoring log:

tail -f filename

Real-time monitoring of 10 lines of log information:

tail -10f filename

View the last 100 lines of log information at the end of the log:

tail -n 100 filename

View the log information after line 100:

tail -n +100 filename

head command to view text information

View the first 100 lines of text:

head -n 100 filename

View the last 100 lines of text

head -n -100 filename

cat command to view text information

View all text content

cat filename

View the contents between certain line ranges in the middle of the text, for example, view the contents between lines 100-120 of the text file:

cat -n filename |tail -n +100|head -n 20

However, I personally don’t like to use this command to locate and view text, because it is too troublesome to view. There will be simpler command operations below the article.

tacView text information

It is a bit opposite to the cat command. The cat command displays the text content from the beginning to the end, while the tac command displays the log content from the end of the text to the beginning.

tac filename

For example, we use the cat command and the tac command to view the same content at the same time:

If you display text using different commands, you will find that the order of the text content is reversed.

Search text content

grep is a powerful text search tool that can use regular expressions to search text and print out matching lines.

Commonly used methods of grep command:

Search in multiple files:

grep "match_pattern" file_1 file_2 file_3 ...

Marker matching color --color=auto option:

grep "match_pattern" file_name --color=auto 

//[The color item here can be selected according to the document description: always, never, auto]

To output all lines except the -v option:

grep -v "match_pattern" file_name

Use the regular expression -E option:

grep -E "[1-9]+"

Only output matching content options:

grep -o -E "[az]+." line

Count the number of lines in the file or text that contain the matching string -c option:

grep -c "text" file_name

Output the number of lines containing matching string -n option:

grep "text" -n file_name

After understanding the functions that the grep command can accomplish, we can use it flexibly in actual work.

Sometimes we may need to view log information for a certain period of time. In this case, we can use the grep command to achieve this function. For example, if we want to view log information within one hour from 22:00 on 2019-08-06, we can enter the following command:

 grep '2019-08-06 22' filename 

This allows you to quickly locate the information range you want to view.

Since the grep command can receive standard input data, we can usually use the pipe command symbol "|" to perform search operations in some standard output.

For example, first read the contents of the file, and then forward the contents to grep with the help of a pipeline for content filtering, as shown in the following command:

cat log.file |grep -n '2019-08-06 22:43'

In addition to using the grep command, you can also use the sed command to achieve the corresponding effect.

sed is a non-interactive editor that processes a file (or input) line by line and sends the results to the screen.

For beginners, it may be more direct to give some practical examples rather than explaining the concepts.

Commonly used methods of sed command:

Print only the first line of the file

sed -n '1p' filename

View the contents between the first line and the tenth line of the file

sed -n '1,10p' filename

Delete the first line of text

sed '1d' filename

Replace certain strings in the text

sed 's/desired content/replaced content/g'
For example: sed 's/1/one /g' filename replaces 1 with one

After understanding some basic usage of the sed command, we can use it many times in actual work scenarios to strengthen our understanding of the sed command.

For example, use the sed command to specify the date range, such as viewing the log records between 2019-08-06 22:43-22:44:

sed -n '/2019-08-06 22:43/,/2019-08-06 22:44/p' filename 

As mentioned above, we can use the head and tail commands together to view a certain section of the log file, but this operation is a bit troublesome. You might as well try using the sed command to perform the operation.

For example, check lines 1-20 of the log:

 nl log.file | sed -n '1,10p' 

Use the more command to turn pages

If the log file you want to view is too large, you can use the more command to search in pages, for example, set each page to display 10 data information:

more -10 filename 

By using the more command, you can view the data displayed on each page, and by pressing the space bar, you can jump to the next page. At the same time, the basic progress of the text content currently being read will also be displayed in the window.

Having said so much, let's simulate some operation scenarios:

View the log record of the last occurrence of the keyword 'test'

 grep 'test' -A 10 log.file | tail -n 11

Here you need to understand the meaning of several parameters of the grep command:

• grep 'name' -A 10 displays the matching content and the following 10 lines
• grep 'name' -B 10 displays the matching content and the previous 10 lines
• grep 'name' -C 10 displays the matching content and the 10 lines before and after it

The tail -n 11 command displays the current 10 lines and the matching line.

Simply count the number of lines containing the keyword 'test' in a log

Corresponding commands:

grep 'test' ./log.file |wc -l

Here we can first output the text content to the standard output, and then use the pipe to pass the data information to the wc command for statistics.

Several commonly used parameters of the wc command

-l Number of lines to match
-w Number of words to match
-m number of characters to match

There are so many techniques for viewing text information in Linux, far more than what I mentioned in the article. Therefore, in actual work, we can also summarize and conclude more techniques that will help us improve our work efficiency.

Summarize

The above is the full content of this article. I hope that the content of this article will have certain reference learning value for your study or work. Thank you for your support of 123WORDPRESS.COM.