Bash basics

Question 1

What are standard streams?

Answer 1

• standard output (stdout)
• standard input (stdin)
• standard error (stderr)

This is the standard for almost all unix apps. Lets us pipe input/output/error to a standard place, and know that it will work because they share this common api.

They let us use redirection.

Question 2

What is redirection and what are the bash commands?

Answer 2

read from stdout
> write stdout to file (overwrites file)
» append stdout to file (e.g. for log files ls&raquo_space; test.log )
< read from stdin
2> read from stderr

Question 3

Command line: how do you show all running processes?

Answer 3

ps

Question 4

Command line: what does grep stand for?

Answer 4

general regular expression

Question 5

Command line: what are the two ways to find things on a unix machine?

Answer 5

grep -i ‘hey’ /opt/iul
grep options search expression directory

• a cool use case would be to grep the auth.log with a regex that catches all unauthorised users, take their IP addresses and pipe them to a ban list.

(zgrep file - searches inside gzip file, this is useful for logs bc over time, logfiles get automatically concatenated into gzip files)

find /bar -name file.txt
find directory options file/folder
useful options:
- type
- name
- empty
- executable
- writable
** finding executable/writable files would for example be useful if you want to check that you set all your permissions correctly.