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# Read a file per line

```
# while read line; do echo "$line"; done < file.txt
```

# Upper to Lower

Is pretty easy done

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

or

```
# echo "LadiDA"|tr '[:upper:]' '[:lower:]'
```

# SED Examples

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

```
# sed -i "/myuser@old.laptop/d"  .ssh/authorized_keys
```

# Calculate

You can use the expr

```
# expr 1 + 2
```

and you will get 3 as result.

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

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

# Bash redirection

stdout to file

```
# command > file.txt
```

stderr to file 

```
# command 2> /dev/null
```

stdout AND stderr to file

```
# command &> file.txt
```

stdout to file AND stderr to file 

```
# command > file.txt 2> /dev/null
```

stdout to stderr

```
# command 1>&2
```

stderr to stdout

```
# command 2>&1
```