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Full Discussion: A puzzle with a printing function executing in background
Top Forums Shell Programming and Scripting A puzzle with a printing function executing in background Post 302488013 by klease on Friday 14th of January 2011 02:34:29 PM
Old 01-14-2011
A puzzle with a printing function executing in background
Somebody on a thread in the (french) Mandriva Forum recently suggested a script, designed to provide a tool to display kind of "temporisation widgets" on the console (to be ultimately pasted in other more complex scripts).
One version of this script was something like the following, which seems to work fine (it displays a spinning cross and it end with just ONE ENTER keystroke) :

(sorry for not having translated comments from french)
Code:
    #!/bin/bash

    # Arrêt par création de fichier
    # Version:1.0.2c
    # Au choix: croix tournante ou barre d'avancement;
    # inverser les commentaires pour sélectionner la boucle du
    # mode choisi. Pour arrêter et revenir à l'invite : taper ENTREE.
    #
    #
    clear;echo

    #+++++++++++++++++++++++++++++++++++++++
    # partie à insérer dans un script (supprimer la boucle superflue)

      PID=$$ # PID du processus père

        trap "rm -f $STOP; exit"  HUP  INT  QUIT  ABRT  TERM

    # Affiche la barre d'avancement (ici 5 motifs/s)
      function barre()
      {
        tput civis;tput bold;tput sc;x=0
        
        # Displays 5 sharps/seconds
       #--------------------------
       # COLS=$(tput cols) # Mémorise la largeur du terminal
       # while : ; do
       #    sleep 0.2
       #    tput rc;tput hpa $x;tput el
       #    echo -n "#"
       #    let "x += 1"
       #    if [ $x = $COLS ]; then tput rc;tput dl1;x=0;fi
       #    if [ -f "$STOP" ]; then break;fi
       #    if [ $((x % 5)) = 0 ]; then # si Ctrl-c a tué le père, arrête le fils
       #        if [ "$(ps h $PID)" = "" ]; then break;fi
       #    fi
       # done
        #--------------------------

        # Displays spinning cross
        #---------------------------------------
           while : ; do
               sleep 0.125;tput rc;tput dl1;echo -n "      |"
               sleep 0.125;tput rc;tput dl1;echo -n "      /"
               sleep 0.125;tput rc;tput dl1;echo -n "      -"
               sleep 0.125;tput rc;tput dl1;echo -n "      \\"
               sleep 0.125;tput rc;tput dl1;echo -n "      |"
               sleep 0.125;tput rc;tput dl1;echo -n "      /"
               sleep 0.125;tput rc;tput dl1;echo -n "      -"
               sleep 0.125;tput rc;tput dl1;echo -n "      \\"
               if [ -f $STOP ]; then break;fi
               if [ "$(ps h $PID)" = "" ]; then break;fi
            done
            #---------------------------------------
        
        rm -f $STOP
        tput rc;tput dl1;tput sgr0;tput cnorm;tput ed
      }

    #++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    # fin de la fonction pour un script

    # Lancement de la fonction barre
      barre &
    # Instructions d'arrêt de la fonction
      read
      STOP=$(mktemp  --suffix=.stop-barre --tmpdir=$HOME/tmp)
      tput rc;tput dl1
      sleep 1       # faire une pause pour revenir en avant-plan
                     # avant d'envoyer une commande d'avant plan.
      exit 0

The problem is now for another version of this script, which is exactly the same with just some commented and uncommented lines, and which displays a line of sharps (#) (five # / second).

It works but - for some reason - it ends and returns to shell invite with TWO ENTER keystrokes.

Code:
    #!/bin/bash

    # Arrêt par création de fichier
    # Version:1.0.2c
    # Au choix: croix tournante ou barre d'avancement;
    # inverser les commentaires pour sélectionner la boucle du
    # mode choisi. Pour arrêter et revenir à l'invite : taper ENTREE.
    #
    #
    clear;echo

    #+++++++++++++++++++++++++++++++++++++++
    # partie à insérer dans un script (supprimer la boucle superflue)

      PID=$$ # PID du processus père

        trap "rm -f $STOP; exit"  HUP  INT  QUIT  ABRT  TERM

    # Displays a bar (with sharps) or a cross
      function barre()
      {
        tput civis;tput bold;tput sc;x=0

        #--------------------------
        COLS=$(tput cols)    # Mémorise la largeur du terminal
        while : ; do
           sleep 0.2
           tput rc;tput hpa $x;tput el
           echo -n "#"
           let "x += 1"
           if [ $x = $COLS ]; then tput rc;tput dl1;x=0;fi
           if [ -f "$STOP" ]; then break;fi
           if [ $((x % 5)) = 0 ]; then # si Ctrl-c a tué le père, arrête le fils
               if [ "$(ps h $PID)" = "" ]; then break;fi
           fi
        done
        #--------------------------

        # Displays spinning cross
        #---------------------------------------
        #   while : ; do
        #      sleep 0.125;tput rc;tput dl1;echo -n "      |"
        #      sleep 0.125;tput rc;tput dl1;echo -n "      /"
        #      sleep 0.125;tput rc;tput dl1;echo -n "      -"
        #      sleep 0.125;tput rc;tput dl1;echo -n "      \\"
        #      sleep 0.125;tput rc;tput dl1;echo -n "      |"
        #      sleep 0.125;tput rc;tput dl1;echo -n "      /"
        #      sleep 0.125;tput rc;tput dl1;echo -n "      -"
        #      sleep 0.125;tput rc;tput dl1;echo -n "      \\"
        #      if [ -f $STOP ]; then break;fi
        #      if [ "$(ps h $PID)" = "" ]; then break;fi
        #   done
            #---------------------------------------
        
        rm -f $STOP
        tput rc;tput dl1;tput sgr0;tput cnorm;tput ed
      }

    #++++++++++++++++++++++++++++++++++++++++++++++++++++++++
    # fin de la fonction pour un script

    # Lancement de la fonction barre
      barre &
    # Instructions d'arrêt de la fonction
      read
      STOP=$(mktemp  --suffix=.stop-barre --tmpdir=$HOME/tmp)
      tput rc;tput dl1
      sleep 1       # faire une pause pour revenir en avant-plan
                     # avant d'envoyer une commande d'avant plan.
      exit 0

Why such different behaviours ? And how to get the second version to end and go back to the shell prompt with just ONE (ENTER) keystroke.

---------- Post updated at 08:34 PM ---------- Previous update was at 08:28 PM ----------

For the french-speaking of you see the discussion about some aspects of this script :
Code:
http://forum.mandriva.com/fr/viewtopic.php?p=840962#p840962

Last edited by klease; 01-15-2011 at 04:08 AM..
 

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