Linux Basic Commands

Redirections, Pipes and Signals
Managing streams

These are the redirectors that we can use to take control of the streams of our programs

    command > file: redirects standard output, overwrites file
    command >> file: redirects standard output, appends to file
    command < file: redirects standard input from file
    command 2> file: redirects standard error to file
    command1 | command2: connects the output of command1 to the input of command2

Operating with processes

These are some commands that are useful to know in Linux when interacting with processes. Not all of them are explained in videos, so feel free to investigate them on your own.

    ps: lists the processes executing in the current terminal for the current user

    ps ax: lists all processes currently executing for all users  
    ps e: shows the environment for the processes listed  

    kill PID: sends the SIGTERM signal to the process identified by PID
    fg: causes a job that was stopped or in the background to return to the foreground
    bg: causes a job that was stopped to go to the background
    jobs: lists the jobs currently running or stopped

    top: shows the processes currently using the most CPU time (press "q" to quit)  

Managing files and directories

    cd directory: changes the current working directory to the specified one
    pwd: prints the current working directory
    ls: lists the contents of the current directory

    ls directory: lists the contents of the received directory  
    ls -l: lists the additional information for the contents of the directory  
    ls -a: lists all files, including those hidden  
    ls -la: applies both the -l and the -a flags  

    mkdir directory: creates the directory with the received name
    rmdir directory: deletes the directory with the received name (if empty)
    cp old_name new_name: copies old_name into new_name
    mv old_name new_name: moves old_name into new_name
    touch file_name: creates an empty file or updates the modified time if it exists
    chmod modifiers files: changes the permissions for the files according to the provided modifiers; we've seen +x to make the file executable
    chown user files: changes the owner of the files to the given user
    chgrp group files: changes the group of the files to the given group

Operating with the content of files

    cat file: shows the content of the file through standard output
    wc file: counts the amount of characters, words, and lines in the given file; can also count the same values of whatever it receives via stdin
    file file: prints the type of the given file, as recognized by the operating system
    head file: shows the first 10 lines of the given file
    tail file: shows the last 10 lines of the given file
    less file: scrolls through the contents of the given file (press "q" to quit)
    sort file: sorts the lines of the file alphabetically
    cut -dseparator -ffields file: for each line in the given file, splits the line according to the given separator and prints the given fields (starting from 1)

Additional commands

    echo "message": prints the message to standard output
    date: prints the current date
    who: prints the list of users currently logged into the computer
    man command: shows the manual page of the given command; manual pages contain a lot of information explaining how to use each command (press "q" to quit)
    uptime: shows how long the computer has been running

    free: shows the amount of unused memory on the current system  

cut:

The cut command extracts a given number of characters or columns from a file. A delimiter is a character or set of characters that separate text strings.

Syntax:

cut [options] [file]

For delimiter separated fields, the - d option is used. The -f option specifies the field, a set of fields, or a range of fields to be extracted.

Syntax:
cut -d [delimiter] -f [field number]