Diff for "BashFAQ/034"

Differences between revisions 1 and 10 (spanning 9 versions)

Can I do a spinner in Bash?

Sure!

i=0
sp='/-\|'
n=${#sp}
printf ' '
while true; do
    printf '\b%s' "${sp:i++%n:1}"
done

Each time the loop iterates, it displays the next character in the sp string, wrapping around as it reaches the end. (i is the position of the current character to display and ${#sp} is the length of the sp string).

The \b string is replaced by a 'backspace' character. Alternatively, you could play with \r to go back to the beginning of the line.

If you want it to slow down, put a sleep command inside the loop (after the printf).

A POSIX equivalent would be:

sp='/-\|'
printf ' '
while true; do
    printf '\b%.1s' "$sp"
    sp=${sp#?}${sp%???}
done

If you already have a loop which does a lot of work, you can call the following function at the beginning of each iteration to update the spinner:

sp='/-\|'
sc=0
spin() {
   printf "\b${sp:sc++:1}"
   ((sc==${#sp})) && sc=0
}
endspin() {
   printf "\r%s\n" "$@"
}

until work_done; do
   spin
   some_work ...
done
endspin

A similar technique can be used to build progress bars.

CategoryShell

-  ⇤ ← Revision 1 as of 2007-05-02 23:23:02 → 
  Size: 725
  Editor: redondos
  Comment:
+   ← Revision 10 as of 2015-05-15 07:51:54 → ⇥
  Size: 1237
  Editor: geirha
  Comment: single quotes to be sure a backslash remains a backslash.
-Deletions are marked like this.
+Additions are marked like this.
 Line 1:
-[[Anchor(faq34)]]
+<<Anchor(faq34)>>
 Line 3:
-Sure.
+Sure!
-Line 5:
+Line 6:
-    i=1
    sp="/-\|"
    echo -n ' '
    while true
    do
        echo -en "\b${sp:i++%${#sp}:1}"
    done
+i=0
sp='/-\|'
n=${#sp}
printf ' '
while true; do
    printf '\b%s' "${sp:i++%n:1}"
done
-Line 14:
+Line 15:
-You can also use \r instead of \b.  You can use pretty much any character sequence you want as well.  If you want it to slow down, put a {{{sleep}}} command inside the loop.
+Each time the loop iterates, it displays the next character in the `sp` string, wrapping around as it reaches the end.  (`i` is the position of the current character to display and `${#sp}` is the [[BashFAQ/007|length]] of the `sp` string).
-Line 16:
+Line 17:
-To use as a function called from a loop on every iteration, for example:
+The `\b` string is replaced by a 'backspace' character.  Alternatively, you could play with `\r` to go back to the beginning of the line.

If you want it to slow down, put a {{{sleep}}} command inside the loop (after the printf).

A POSIX equivalent would be:
-Line 18:
+Line 24:
-sp="/-\|"
+sp='/-\|'
printf ' '
while true; do
    printf '\b%.1s' "$sp"
    sp=${sp#?}${sp%???}
done
}}}

If you already have a loop which does a lot of work, you can call the following function at the beginning of each iteration to update the spinner:
{{{
sp='/-\|'
-Line 21:
+Line 37:
-   echo -ne "\b${sp:sc++:1}"
   ((sc==4)) && sc=0
+   printf "\b${sp:sc++:1}"
   ((sc==${#sp})) && sc=0
-Line 24:
+Line 40:
+endspin() {
   printf "\r%s\n" "$@"
}

until work_done; do
   spin
   some_work ...
done
endspin
-Line 25:
+Line 50:
-When printing the next output line (ie when the spin is over) use: {{{ echo -e "\r$line" }}} or: {{{ echo -en '\r'; echo "$line" }}}
-Line 27:
+Line 51:
-A similar technique can be used to build progress bars.
+A similar technique can be used to build [[BashFAQ/044|progress bars]].

----
CategoryShell