Summing numbers in a column

To sum several values in column from file we can use paste command and bash arithmetic expressions

$ echo $(($(paste -s -d'+' nums)))

I've always used tr to glue the values into one line, but the remaining '+' sign must be removed:

$ echo $(($(cat nums | tr '\n' '+' |sed 's/.$//')))

Or with awk:

$ awk '{s+=$1}; END { print s}' nums

wget and line delimiters CR LF

If you download file with wget and the filename comes from windows file, the output filename will always have %0D at the end. To get rid of this, instead of:

wget $filename

use

wget $(echo "$filename" | tr -d '\r')

This will do the trick

Generating strong passwords

Sometimes we need to make up the password. Normally the password should be easy to remember but hard to guess. I show you how to generate strong passwords that are not easy to remember :). We'll use for this purpose /dev/urandom device, which generates random data. Suppose we want to generate 10 passwords, each 8 characters long. To achieve this we type:

$ cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -8 | head -10
lUrBzyuv
RuDq498i
mOzJMs4Y
s0lUpMZd
LmwuN6Sy
fubIOO6g
KKynsPs4
dFH4W0Ux
3JAbwJQD
PofhRhTS

The fold command breaks each line after n characters, so defines the length of the password, the head command shows first n lines so defines the number of passwords. The tr deletes (-d) all but specified (-c) characters. The idea comes from here.