Linux Programming

Acknowledgment to tutorialspoint.

https://www.tutorialspoint.com/unix/index.htm

You can use the cat command to see the content of a file and display the line numbers by using the -b option along with the cat command as follows

cat -b filename

You can use the wc command to get a count of the total number of lines, words, and characters contained in a file. 

wc filename

To make a copy of a file use the cp command.

cp source_file destination_file

To go in your last directory

cd -

To list the files in a directory

ls dirname

An important Unix concept is the environment, which is defined by environment variables. Some are set by the system, others by you, yet others by the shell, or any program that loads another program.

A variable is a character string to which we assign a value. The value assigned could be a number, text, filename, device, or any other type of data. For example, first we set a variable TEST and then we access its value using the echo command 

TEST="Unix Programming"
echo $TEST

It produces the following result.

Unix Programming

If we don't use the $ sign, it returns

TEST

Really clear a terminal instead of simply shifting previous output upwards when you run "clear" command.

tput reset

You can connect two commands together so that the output from one program becomes the input of the next program. Two or more commands connected in this way form a pipe. To make a pipe, put a vertical bar (|) on the command line between two commands. When a program takes its input from another program, it performs some operation on that input, and writes the result to the standard output. It is referred to as a filter.

The name "grep“ means "globally search for a regular expression and print all lines containing it”. For example,

ls -l | grep "lib"

There are various options which you can use along with the grep command

ls -l | grep -v "lib" # Prints all lines that do not match pattern.
ls -l | grep -c "lib" # Prints only the count of matching lines.
ls -l | grep -i "lib" # case insensitive search

View the history of a command

history|grep "main.py" # view all commands containing main.py

 Write the output of a command to a txt file

command >>logs.txt 2>&1 # errors and warnings included

 Disk usage of all users

sudo du -shc /home/*

Disk usage by subfolder

du directory-to-analyze/* -sh

Find the process on a specific port

sudo lsof -t -i:9001

　　

转载于:https://www.cnblogs.com/cxxszz/p/8573773.html