Which process uses port 8080?

# fuser 8080/tcp

Bash: How to zip a folder (.zip)

$ zip -r foo.zip foo

Replace new line with a space

$ tr '\n' ' '

how to mount .iso

$ sudo mount -o loop /media/cdrom foo.iso

send e-mails from a shell script including file attachments

Install uuencode:

$ sudo apt-get install sharutils

Remove empty lines from txt

$ sed '/^$/d' input.txt > output.txt

Replace a string with another string in all files

$ sed -i 's/old-word/new-word/g' *.txt

$ perl -pie 's/old-word/new-word/g' input > output

References
http://www.cyberciti.biz/faq/unix-linux-replace-string-words-in-many-files/

Default parameter values in Bash