Useful linux commands

disk space :  df -h

disk space by folder :  du -sk * | sort -n

file/dir sizes :  du -hs

Remove directory : rm -rf

Count files in folder : ls | wc -l

Count lines in text file : wc -l emails.txt

Emails in file : grep -Eiorh '([[:alnum:]_.-]+@[[:alnum:]_.-]+?\.[[:alpha:].]{2,6})' “$@” * | sort | uniq > emails.txt

Find files with text : find . -type f -exec grep -H "text-to-find-here" {} \;

List machine users : cut -d: -f1 /etc/passwd

Version Ubuntu : lsb_release -a

php version : php --version

mySQL version : mysql --version

Update(Mise à jour) Ubuntu : apt-get update && apt-get upgrade -y

To replace a string in multiple files you can use:

grep -rl matchstring somedir/ | xargs sed -i 's/string1/string2/g'

E.g.

grep -rl 'windows' ./ | xargs sed -i 's/windows/linux/g'