GNU/Linux

---

How to: Extract all usernames that are logged in from who

7 November 2014  in Bash / GNU/Linux / HowTos  tagged bash / cut / GNU/Linux / grep / howtos / sort / unique / who by Tux

who | cut -d ' ' -f 1 | sort -u

who: will show who is logged on

cut  -d ‘ ‘ -f 1: will remove all sections from each line except for column 1. It will use the space character as the delimiter for the columns

sort -u: it will sort the usernames and remove duplicate lines. So if a user is logged in multiple times you will get that username only once.
In case you want to filter out root user from this list you can do it as follows:

who | cut -d ' ' -f 1 | sort -u | grep -v 'root'


---

Generate Random Password

27 October 2014  in Bash / GNU/Linux / HowTos  tagged base64 / bash / date / GNU/Linux / head / howtos / password / random / sha256sum by Tux

date +%s | sha256sum | base64 | head -c 32 ; echo
date +%s : will print the system date and time in seconds since 1970-01-01 00:00:00 UTC

sha256sum :  will compute  the SHA256 message digest of the time in seconds we produced before

base64 : will encode the previous data and print them to standard output

head -c 32 : will print the first 32 characters of the previous data

; echo : is used to create a new line at the end of the results

---

Bash: Echo – Print with out changing line

26 October 2014  in Bash  tagged \n / bash / echo / GNU/Linux / new line by Tux

We use the -n flag which instructs echo not to output the trailing newline.

echo -n ${percentage}

---

Linux Bash: How to print leading zeroes on a variable

24 February 2012  in Bash / GNU/Linux  tagged bash / GNU/Linux / leading zeroes by Tux

In order to print the leading zeros to a variable you need to use the function printf as follows, where %03d states that the number should consist of minimum 3 digits and thus it will put the missing leading zeros:

 printf %03d $counter

The following example renames a file that it has the following format for a filename: number.anything and adds the leading zeros in order to make it easier while sorting multiple files.
The name is contained in the variable $a.
If for example we had the file 11.txt  it will become 0011.txt

mv $a `printf %04d.%s ${a%.*} ${a##*.}`

 

---

---