Writing a simple GUI for a simple bash script

Question

I have a bash script which makes some system changes involving a list of URL addresses beginning with "http", and I'm trying to write a GUI for it.

I'm stuck with the following last part:

changes="$(cat /home/$USER/.updates.log | grep http)"
if [ "$changes" != 0 ]; then
    zenity --question --text "Changes found in:\n$changes\n\nWould you like to update now?"
        if [ $? = 0 ]
        then
# password
sudo_password="$(gksudo --print-pass --description 'MyScript' -- : 2>/dev/null)"
# check for null entry or cancellation
if [[ ${?} != 0 || -z ${sudo_password} ]]
then
    exit 4
fi
if ! sudo -kSp '' [ 1 ] <<<"${sudo_password}" 2>/dev/null
then
    exit 4
fi
# notify
notify-send "Applying updates..." -i gtk-dialog-info -t 1000 -u normal &
# proceed to update
cuser="${SUDO_USER:-$USER}"
sudo -Sp ''  sudo /usr/local/bin/MyScript <<<"${sudo_password}"
# option to view log
new_update="$(cat /home/$USER/.updates.log | grep 'MyScript completed at ' | awk -F ' at ' '{print $2}')"
zenity --question --text "MyScript updated at $new_update\n\nWould you like to view the log file now?"
if [ $? = 0 ]
then
# display log
    zenity --text-info --filename=/home/$USER/.updates.log --width 680 --height 680
fi
fi
fi

Actually, it seems the tricky part for me is here:

if [ "$changes" != 0 ]; then

I want to simply display a message like "No updates found; exiting..." if that file contains no lines beginning with "http" but this simply creates a blank line in the zenity question dialog box. It seems I need to modify this line, and also add another command under "else" but I just don't know how and where...

Answer 1

I can't test the rest of your script since I don't have the necessary data and don't even know what it does but this line is certainly wrong:

changes="$(cat /home/$USER/.updates.log | grep http)"

That will save the output of your grep command in $changes, not the number of times the string was found, but the actual lines returned. For example:

$ cat file 
one http
two http
three http
$ changes=$(cat file | grep http)
$ echo "$changes" 
one http two http three http

As you can see above, $changes is just each matching line from the file concatenated into a single variable. What you wanted was something like (no need for cat, by the way, grep can take a filename as input):

$ changes=$(grep -c http file)
$ echo $changes 
3

The -c switch makes grep print the number of matching lines instead of the lines themselves. Alternatively, you can pass the output through wc -l to count the lines:

changes=$(grep http file | wc -l)

Either one will do and you will now be able to check whether $changes is greater than 0:

if [ "$changes" -gt 0 ]]; then 
        ...
fi

If you want to display the changes, use your original approach but don't compare it to 0. Instead, use -z to check whether the variable is empty:

changes=$(grep http /home/$USER/.updates.log)
## If $changes is empty
if [ -z "$changes" ]
then
     notify-send "Found no updates; exiting..." -i gtk-dialog-info -t 1000 -u normal &
     exit
else
     zenity --question --text "Changes found in:\n$changes\n\nWould you like to update now?"
    ...
fi

Answer 2

About the problem WHERE to put the rest of the condition, the hint is to always respect the indentation, it surely make easier the task : )

I've not tested it (I could be wrong), but I would try something like this for begin:

changes="$(cat /home/$USER/.updates.log | grep http)"
if [ "$changes" != 0 ]; then
  zenity --question --text "Changes found in:\n<i>$changes</i>\n\nWould you like to update now?"
  if [ $? = 0 ]; then
    ## password
    sudo_password="$(gksudo --print-pass --description 'MyScript' -- : 2>/dev/null)"
    ## check for null entry or cancellation
    if [[ ${?} != 0 || -z ${sudo_password} ]]; then
      exit 4
    fi
    if ! sudo -kSp '' [ 1 ] <<<"${sudo_password}" 2>/dev/null; then
      exit 4
    fi
    ## notify
    notify-send "Applying updates..." -i gtk-dialog-info -t 1000 -u normal &
    ## proceed to update
    cuser="${SUDO_USER:-$USER}"
    sudo -Sp ''  sudo /usr/local/bin/MyScript <<<"${sudo_password}"
    ## option to view log
    new_update="$(cat /home/$USER/.updates.log | grep 'MyScript completed at ' | awk -F ' at ' '{print $2}')"
    zenity --question --text "MyScript updated at <b><i>$new_update</i></b>\n  \nWould you like to view the log file now?"
    if [ $? = 0 ]; then
      ## display log
      zenity --text-info --filename=/home/$USER/.updates.log --width 680 --height 680
    fi
  fi
## Here is where you can choose what to do if there are no results
else
  zenity --text-info "No updates found; exiting..." 
fi