Command line research

This is me learning the command line.

Control key shortcuts

• CTRL + A – takes you to the beginning of the line
• CTRL + E – takes you to the end of the line
• CTRL + K – "yank" everything after the cursor
• CTRL + U – "yank" everything before the cursor
• CTRL + Y - "paste" (paste in quotes because it doesn't actually go into your system clipboard) everything you yanked
• CTRL + L - clear the screen
• CTRL + R – reverse search through history

Signals

• CTRL + C - SIGINT -- Interrupt Signal - signal to interrupt what it's doing and stop.

• CTRL + D - SIGQUIT -- Quit Signal - Force quit the program.

• SIGTERM signal

  • kill command or when the computer is shutting down
  • usually the computer sends this signal and not us
  • telling the programs to shut down

• SIGKILL - when we run kill -9 or kill -SIGKILL - when we want a program to force shut down now.

There are other signals. Run kill -l to list them.

Escaping with backslash

touch file\?.txt # creates 'file?.txt' # escaped the ? operator
touch file\ .txt # creates 'file .txt' # escaped white space ' '
touch file\\.txt # creates 'file\.txt' # escaped backslash

Replacements

Shells like bash and sh support replacements

touch file{1,2,3}.txt # is the same as touch file1.txt file2.txt file3.txt

touch file-{a,b,c}.txt # is the same as touch file-a.txt file-b.txt file-c.txt

# you can just put a comma for one without the expansion

touch file{1,}.txt # will create file.txt and file1.txt

Shells support this and not the programs

Wildcards

We can use wildcards with *

ls file* # lists all files starting-with file

ls fil*.txt # lists all files that starts with fil and ends with .txt

The ? operator - exactly one character

The ? operator lets you exactly one character unlike the wildcard

ls file?.txt # will match file1.txt but won't match file12.txt

start..end..skip operation - from start till end

• We can the start..end..skip syntax to append get numbers/letters from start til end.

touch file{1..5}.txt # creates file1.txt file2.txt all the way to file5.txt

touch file-{a..z}.txt # creates file-a.txt file-b.txt all the way to file-z.txt

• You can also backwards from z to a and likewise with numbers

echo {5...1} # prints 5 4 3 2 1

echo {z..a} #prints z y x w v u t s r q p o n m l k j i h g f e d c b a

• We can also skip some numbers but not letters

touch file{1..5..2}.txt # creates file1.txt file3.txt and file5.txt and skipped 2 and 4 ( every 2nd number)

This won' work with letters

• We can combine two or more of these

echo {z..x}{1..4} # z1 z2 z3 z4 y1 y2 y3 y4 x1 x2 x3 x4

Attribution

• Most of these notes and commands from Brian Holt's complete intro to Linux and the command line course

• Brian Holt has made the course notes free for everyone which you can access here