Diff for "BashFAQ/040"

How do I use dialog to get input from the user?

Here is an example:

  # POSIX
  foo=$(dialog --inputbox "text goes here" 8 40 2>&1 >/dev/tty)
  echo "The user typed '$foo'"

The redirection here is a bit tricky.

1. The foo=$(command) is set up first, so the standard output of the command is being captured by bash.

2. Inside the command, the 2>&1 causes standard error to be sent to where standard out is going -- in other words, stderr will now be captured.

3. >/dev/tty sends standard output to the terminal, so the dialog box will be seen by the user. Standard error will still be captured, however.

Another common dialog(1)-related question is how to dynamically generate a dialog command that has items which must be quoted (either because they're empty strings, or because they contain internal white space). One can use eval for that purpose, but the cleanest way to achieve this goal is to use an array.

  # Bash
  unset m; i=0
  words=(apple banana cherry "dog droppings")
  for w in "${words[@]}"; do
    m[i++]=$w; m[i++]=""
  done
  dialog --menu "Which one?" 12 70 9 "${m[@]}"

In this example, the while loop that populates the m array could have been reading from a pipeline, a file, etc.

Recall that the construction "${m[@]}" expands to the entire contents of an array, but with each element implicitly quoted. It's analogous to the "$@" construct for handling positional parameters. For more details, see FAQ #50.

Here's another example, using filenames:

  # Bash
  files=(*.mp3)       # These may contain spaces, apostrophes, etc.
  cmd=(dialog --menu "Select one:" 22 76 16)
  i=0 n=${#cmd[*]}
  for f in "${files[@]}"; do
      cmd[n++]=$((i++)); cmd[n++]="$f"
  done
  choice=$("${cmd[@]}" 2>&1 >/dev/tty)
  echo "Here's the file you chose:"
  ls -ld -- "${files[choice]}"

A separate but useful function of dialog is to track progress of a process that produces output. Below is an example that uses dialog to track processes writing to a log file. In the dialog window, there is a tailbox where output is stored, and a msgbox with a clickable Quit. Clicking quit will cause trap to execute, removing the tempfile, and destroying the tail process.

  # POSIX(?)
  # you cannot tail a nonexistent file, so always ensure it pre-exists!
  rm -f dialog-tail.log; echo Initialize log >> dialog-tail.log
  date >> dialog-tail.log
  tempfile=`tempfile 2>/dev/null` || tempfile=/tmp/test$$
  trap 'rm -f $tempfile; stty sane; exit 1' 1 2 3 15
  dialog --title "TAIL BOXES" \
        --begin 10 10 --tailboxbg dialog-tail.log 8 58 \
        --and-widget \
        --begin 3 10 --msgbox "Press OK " 5 30 \
        2>$tempfile &
  mypid=$!
  for i in 1 2 3;  do echo $i >> dialog-tail.log; sleep 1; done
  echo Done. >> dialog-tail.log
  wait $mypid
  rm -f $tempfile

For an example of creating a progress bar using dialog --gauge, see FAQ #44.

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