To extract a column of data from multiple column, we can use cut. Usually cut use to extract value from huge trace file or data file such as /etc/passwd.
To extract all available user name from /etc/passwd, you can do this
cut -d":" -f1 /etc/passwd
Cut extract value line by line, to put all into 1 line, you can use xargs
cut -d":" -f1 /etc/passwd | xargs echo