Linux System Administration

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Appendix: bash Script Samples

# Check whether the user already exists.

# If so, report this and skip this user.

result=$( egrep "^$username:" < /etc/passwd )

if [[ -n "$result" ]] ; then

echo "User '$username' already exists"

continue

fi

# Check whether the group already exists.

# If not, add the group.

result=$( egrep "^$groupname:" < /etc/group )

if [[ -z "$result" ]] ; then

groupadd "$groupname"

fi

# Add the user.

useradd -c "$realname" \

-d "/home/$username" \

-e "$expiredate" \

-f 365 \

-g "$groupname" \

-m \

-s /bin/bash \

"$username"

if [[ $? == 0 ]]; then

echo "Successfully added user '$username'."

else

echo "Error adding user '$username' (group \

'$groupname', real name '$realname')"

exit 1

fi

done

Random Password Generator

Here’s a script that generates a password of any requested length, in ASCII characters:

#!/bin/bash

n="$1"

[[ -n "$n" ]] || n=12

if [[ $n -lt 8 ]]; then

echo "A password of length $n would be too weak"

exit 1

fi

p=$( dd if=/dev/urandom bs=512 count=1 2>/dev/null \

| tr -cd 'a-zA-Z0-9' \

| cut -c 1-$n )

echo "${p}"

Random Password Generator

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If this makes perfect sense to you as it stands, you deserve a reward.

*

While you’re

out, the rest of us will look a bit more closely at the inherent flaws in this code.

This code is typical of something you might inherent ...