Diff for "BashFAQ/034"

Differences between revisions 1 and 11 (spanning 10 versions)

Can I do a spinner in Bash?

Sure!

i=0
sp='/-\|'
n=${#sp}
printf ' '
sleep 0.1
while true; do
    printf '\b%s' "${sp:i++%n:1}"
    sleep 0.1
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.

To slow it down, the sleep command is included inside the loop (after the printf).

A POSIX equivalent would be:

sp='/-\|'
printf ' '
sleep 0.1
while true; do
    printf '\b%.1s' "$sp"
    sp=${sp#?}${sp%???}
    sleep 0.1
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
    sleep 0.1
}
endspin() {
    printf "\r%s\n" "$@"
    sleep 0.1
}

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 11 as of 2017-03-31 05:19:47 → ⇥
  Size: 1320
  Editor: r180-216-10-159
  Comment: Added `sleep 0.1` after each `printf` to mitigate cpu stress.
-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=${#sp}
printf ' '
sleep 0.1
while true; do
    printf '\b%s' "${sp:i++%n:1}"
    sleep 0.1
done
-Line 14:
+Line 17:
-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 19:
-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.

To slow it down, the `sleep` command is included inside the loop (after the `printf`).

A POSIX equivalent would be:
-Line 18:
+Line 26:
-sp="/-\|"
+sp='/-\|'
printf ' '
sleep 0.1
while true; do
    printf '\b%.1s' "$sp"
    sp=${sp#?}${sp%???}
    sleep 0.1
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 42:
-   echo -ne "\b${sp:sc++:1}"
   ((sc==4)) && sc=0
+    printf "\b${sp:sc++:1}"
    ((sc==${#sp})) && sc=0
    sleep 0.1
-Line 24:
+Line 46:
+endspin() {
    printf "\r%s\n" "$@"
    sleep 0.1
}

until work_done; do
   spin
   some_work ...
done
endspin
-Line 25:
+Line 57:
-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 58:
-A similar technique can be used to build progress bars.
+A similar technique can be used to build [[BashFAQ/044|progress bars]].

----
CategoryShell