BASH - ifステートメントが正しく機能しません。

以下のスクリプトを一度実行しましたが、enforce_for_root一致するものが見つかった場合は行末に追加されました。ただし、何らかの理由でエントリがすでに存在していても、pam_pwquality.soifを入力し続けます。if ! grep -q "enforce_for_root" /etc/pam.d/system-auth

#!/bin/bash
source oem.properties

log_error() {
    echo "Error: $1" | /usr/bin/tee $ERROR_LOG
    echo "Aborting program ... "
    echo " "
    exit 10
}

echo " "
echo -n "Generating SSH keys ... "
if [ -f /home/rlee/.ssh/keys/$RSYNC_KEY ]; then
    echo "key exists, skipping."
else
    sudo -u rlee ssh-keygen -b 4096 -t $RSYNC_KEY_TYPE -f /home/rlee/.ssh/keys/$RSYNC_KEY -C "$RSYNC_KEY_COMMENT" -q -N ""
    if [ $? -ne 0 ]; then log_error "Generating SSH keys."; fi
    echo "OK"
fi
echo " "

echo "Add the public key to old OEM server."
echo "Create or modify the authorized_keys file on the old server."
echo "vim /home/rsync/.ssh/authorized_keys"
echo " "
echo "Add the following key: "
while true
do 
    cat /home/rlee/.ssh/keys/$RSYNC_KEY.pub
    echo " "
    read -p "Press 'C' to continue: " OPTION
    if [ $OPTION == 'C' ] || [ $OPTION == 'c' ]; then break; fi
done

echo -n "Testing SSH connection ... "
ssh -p $OLD_OEM_PORT -i /home/rlee/.ssh/keys/$RSYNC_KEY -o StrictHostKeyChecking=no rsync@$OLD_OEM_HOSTNAME exit
if [ $? -ne 0 ]; then log_error "Testing SSH connection ... "; fi
echo "OK"

useradd llee
useradd nagios

# Enforce password policies
echo -n "Setting password policies ... "
authconfig --enablereqlower --enablerequpper --enablereqdigit --enablereqother --passminlen=12 --passmaxrepeat=3 --update
if [ $? -ne 0 ]; then log_error "Setting password policies ... "; fi
echo "OK"

echo -n "Enforcing password policies on root ... "
if ! grep -q "enforce_for_root" /etc/pam.d/system-auth; then
    
    sed -i -e '/pam_pwquality.so/s/$/ enforce_for_root/' /etc/pam.d/system-auth
    echo "doesn't exist"
fi
if [ $? -ne 0 ]; then log_error "Enforcing password policies on root ... "; fi

exit 

adduserこのコードブロックをステートメントの前の任意の場所に移動すると、if ! grep -q "enforce_for_root" /etc/pam.d/system-auth期待どおりに機能しません。

なぜこれが起こるのですか？

#!/bin/bash

log_error() {
    echo "Error: $1" | /usr/bin/tee $ERROR_LOG
    echo "Aborting program ... "
    echo " "
    exit 10
}


echo -n "Enforcing password policies on root ... "
if ! grep -q "enforce_for_root" /etc/pam.d/system-auth; then
    
    sed -i -e '/pam_pwquality.so/s/$/ enforce_for_root/' /etc/pam.d/system-auth
    echo "doesn't exist"
fi
if [ $? -ne 0 ]; then log_error "Enforcing password policies on root ... "; fi