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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 ```