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I need to write a script that prompts the user to enter a username and then if that username exists, lists all of the user's information from the password file and a list of all commands they are currently running. So far I have this: 

#!/bin/bash

echo "Please enter username"
read username

if [ "$username" = cat /etc/passwd | cut -d: -f1 ]
then 
    //list all user info from passwd file
    id $username

    //list all commands they are running
    i dont know how to code this
fi

If you guys can help me fill in or change anything that will be great, thanks!

Scooby
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  • And for checking if the user exists: https://unix.stackexchange.com/a/272639/70524 – muru Nov 06 '19 at 02:53
  • @muru so is my if conditional right? – Scooby Nov 06 '19 at 03:08
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    @Scooby Even if your `cat` command was used with a command substitution like `"$(cat … | cut …)"`, you would compare `$username` against the list of all usernames and this would very likely fail. Instead you could use `grep` with `if grep -q "^${username}:" /etc/passwd; then …` or test if the username exists with `if id "$username" >/dev/null 2>&1; then …` discarding the output of stdout and stderr. – Freddy Nov 06 '19 at 04:03
  • While you're learning (and even when you think you're not) I'd recommend https://shellcheck.net/ for reviewing your code. – roaima Nov 06 '19 at 12:04

1 Answers1

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Ok, it is pretty clear that you are being asked to work with grep and pgrep so you can do this (no loops, no conditionals, no cutting etc.)

#!/bin/bash
echo "USERNAME:"
read u

#echo "USERNAME CHOSEN: $u"

if ! grep -e "^$u" /etc/passwd >/dev/null; then
echo NO SUCH USER!!!
exit
fi

echo  -e "\v user:$u info from /etc/passwd: "

grep "^$u" /etc/passwd


echo -e "\v USERS COMMANDS" 
echo "PID       CMD"

pgrep -u $u -a |awk '{print $1,"\t",$2}'
NetIceCat
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    Using `if ! getent passwd "$u"; then echo no such user; exit 1; fi` would shorten it and allow for use on systems running directory servers (except it would fail on macOS). It would also return a failure to the calling shell. You do the same `grep` twice, which is not needed (just don't redirect the first one to `/dev/null`), and you will match `pauline` if given the username `paul`. – Kusalananda Nov 06 '19 at 06:42