Bash

I use Linux on a daily basis at work and at home. This section is to remind me of how to carry out certain tasks. It may vary slightly as I use bash at home, but my work environment is set to tcsh.

To see your environment variables
printenv

To add an existing user to an existing group
sudo usermod -a -G group user

Disk Space

To see how much disk space is available in the current directory

df -h (disk free -human-readable)

To see which directories are taking up space

du -sh *

The above command will show you the size of the subdirectories of the current directory.

 

Regular Expressions

Meta character matching

Match any character with the following metas
\d match any number 0-9
\d\d match any two numbers 0-9
\w A-Z a-z 0-9 Any alphanumeric character
\s any whitespace, for example space or tab
. dot matches any character
\W not a word character
\S not whitespace

Anchors

^ Will look for a selection at the beginning of a string, e.g. ‘^To’ will find a line starting with the word To

$ Will look for a selection at the end of a string

Tip: Check for an empty line with grep ‘^$’

Ranges

Ranges are denoted by []

[A-Za-z] Any upper case of lower case letter

[0-9] Any digit

Boundaries

\s whitespace

\b word boundary

Quantifiers

Rather than using the \d\d example shown above, it is possible to use quantifiers to describe how many of a type of character we are looking for.
* 0 or more
+ 1 or more (at least one)
? 0 or 1 (optional character)
{min,max} Minimum or maximum number or characters
{n} Specific number of characters