/advanced_bash_commands

Primary LanguageRuby

Advanced bash notes

Linux is extensionless

.txt means nothing!

Everything is a file

Linux permisions

Things a user can do:

  • Read(r)
  • Write(w)
  • Execute(x)

Users that exist

  • owner Typically the person who creates the file. however it can be changed.
  • group Every file belongs a single group. Groups have many users in it and give access to multiple people
  • others Everyone else not in a group or the owner.

Command to change the permissions of file editing:

chmod <path/file>

Streams, Redirect & Piping

  • STDIN
    • Standard Input
    • STDIN code is 0
  • STDOUT
    • Standard Output
    • STDOUT code is 1
  • STDERR
    • Standard Error
    • STDERR code is 2

Piping & Redirects

Means we can join all of these amazing commands together 🌮

Redirecting:

This is redirecting of STDOUT

ls > list_of_ls.txt wc words.txt > word_count.txt cat words.txt >> word_count.txt

This is redirecting of STDIN

wc < words.txt

This is redirecting of STDERR

ls non_existing_directory 2 > ls_log.txt

the 2 is very important for logging the error.

(if the non_existing_directory doesn't exist, this will send the error to the log file)

Piping |

We sent STDOUT and STDERR into files, but what we want is to be able to send outputs into other programs. This is very powerful and is called Piping 🌮

ls | head -3 ls | tail -3 | sort cat example.txt | grep When

Process management

Running an instance of a program is a process

  • top: top processes
  • ps: processes
  • ps aux: processes auxiliary (all)
  • ps aux | grep vagrant > ps_vagrant_logs.txt: gets only the processes with vagrant in them, inputs to log file for errors
  • ps aux | grep vagrant sqjed 231 2 >> ps_vagrant_logerror.txt: gets the error (using 2) messages made by this command, appends it to a file
to kill, use kill and pid (process id)
  • kill (pid) (pid = process)

Variables

  • We can store variables in bash with MY_VAR = ???
  • We can call them with $MY_VAR, e.g. echo $MY_VAR, which will print whatever is stored in your variable to the command line.
  • If the variables are called in a file/script, we cannot access them by running the file in bash, they will be identified as empty when this occurs.
  • We need to export the variables first, then they become persistent enough for us to use.