Assignment

Let’s use the /etc/passwd file as an example to practice the use of shell pipelines. The passwd file stores basic information of each user account on a Linux/Unix machine.

I have an example passwd file stored at the shared workspace for our activity today. Once you log into the plank server, take a further look at the file to see what information is stored and familiarize yourself with the file format:

$ less /thayerfs/courses/22spring/cosc050/workspace/passwd

Press q to quit the viewing of the less command.

Write pipelines to:

  1. output the list of user full names, sorted alphabetically (remove duplicated occurrences of identical names)
  2. count the number of users with ‘James’ as the first name.
  3. count the number of different shells used by all users.
  4. output the number of users using each type of shell in the descending order.

Solutions

We can define a variable to represent the file:

$ passfile=/thayerfs/courses/22spring/cosc050/workspace/passwd

1. cut -d : -f 5 "$passfile" | sort -u
2. cut -d : -f 5 "$passfile" | sort -u | cut -d ' ' -f 1 | grep -c James
3. cut -d : -f 7 "$passfile" | sort -u | sed '/^$/d' | wc -l
4. cut -d : -f 7 "$passfile" | sed "/^$/d" | sort | uniq -c | sort -nr