====== Read a file per line ======

<code>
# while read line; do echo "$line"; done < file.txt
</code>

====== Upper to Lower ======

Is pretty easy done

<code>
# cat /path/to/file.txt|tr '[:upper:]' '[:lower:]'
</code>

or

<code>
# echo "LadiDA"|tr '[:upper:]' '[:lower:]'
</code>

====== SED Examples ======

Delete a line with a string in it. For example old ssh-keys:

<code>
# sed -i "/myuser@old.laptop/d"  .ssh/authorized_keys
</code>

====== Calculate ======

You can use the expr

<code>
# expr 1 + 2
</code>

and you will get 3 as result.

Also some more fancy stuff is possible. For example in a for-loop:

<code>
for i in {1..9}; do echo "10.20.30.$(expr $i + 40)   servername-$i"; done
</code>

====== Bash redirection ======

stdout to file

<code>
# command > file.txt
</code>

stderr to file 

<code>
# command 2> /dev/null
</code>

stdout AND stderr to file

<code>
# command &> file.txt
</code>

stdout to file AND stderr to file 

<code>
# command > file.txt 2> /dev/null
</code>

stdout to stderr

<code>
# command 1>&2
</code>

stderr to stdout

<code>
# command 2>&1
</code>