Linux Shell Tricks

1. Linux shell tricks

2. Topics

3. Topics
● Me talking
○ Useful key combinations
○ Basic commands
○ Special shell expressions
○ Pipes and redirects
○ On-the-fly “scripts”
○ vim survival guide
○ Customizing the shell
● You doing
○ Get information from a set of
log files
● Q&A

4. Key combinations

5. Key combinations
Ctrl+C Panic button. Usually stops what’s going on (C = Cancel)
↑, ↓ Move through previous commands
Ctrl+R Search in history. (Start typing to search, arrow keys to use + modify command)
Ctrl+Z Suspend current program without terminating it. Resume with fg

6. Basic commands

7. Basic commands
ls List files du Show disk usage of files
touch Create a file or update mtime df Show free disk space
mkdir / rmdir Create/delete directory lsof List open files / sockets
rm Delete file ssh Secure shell on another machine
find Find files and directories xargs Run command for every line of input
cat Show file contents sed Modify text files
less Show file contents for users cut Select columns
grep Find text in file(s) man Get Help
head, tail Get first / last lines

8. Special chars

9. Special shell expressions
* Match 0, 1 or more characters in file names
? Match exactly 1 character in file names
{N..M} Generate a sequence of numbers from N to M
`...` Backticks: Execute the command between the backticks and insert the output at that place
~ The home directory
Shell expansions
Often-used characters
- Dash: The previous ‘thing’ (cd, git, …) or the input (cat)
-- Double dash: End of arguments (more on that later)

10. Pipes and Redirects

11. Pipes and redirects
Input:
● standard input (“STDIN”)
○ usually the user typing on their keyboard
Outputs:
● standard output (“STDOUT”)
○ usually printed on the screen
● standard error (“STDERR”)
○ usually printed on the screen

12. Pipes and redirects
| Pipe: pass the output of one program to another program
> Save the output of a program into a file, deletes the old file contents!
>> Same as >, but appends to the original file (creates the file if necessary)
< Pass the contents of a file as input to the program
2>, 2>> Same as >, >> but for error output
&1 Instead of a filename, this is the standard output.
For example: 2> &1 redirects the error output to standard output.

13. On-the-fly scripts

14. On-the-fly scripts
● Chain commands with ;
● Sub shells with ( )
● loops with for and while

15. vim survival guide

16. vim survival guide
The first thing you do when bad things happen: Get a clean state
● ESC ESC ESC ^C ^C ESC ESC
Edit text: Hit I (“insert mode” - then vim works almost like an ordinary editor).
● Leave insert mode with ESC
Undo: Hit U (press repeated times to go back further)
Copy & Paste:
● Start selection with v or Shift+V (whole lines)
● Hit Y to copy or D to cut. Move to new position and hit p
Save and quit: type “:wq” and hit Return
Quit without saving: “:q!” + Return

17. Shell Customizations

18. Hands-On

19. Hands-On
Log file processing:
● Count the occurrences of HTTP status codes
● Get a list of customer IDs which were denied for manual refunds