<<Anchor(faq34)>>
== Can I do a spinner in Bash? ==
Sure!

{{{
# Bash, with GNU sleep
spin() {
  local i=0
  local sp='/-\|'
  local n=${#sp}
  printf ' '
  while sleep 0.1; do
    printf '\b%s' "${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 [[BashFAQ/007|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:

{{{
# POSIX sh
spin() {
  sp='/-\|'
  printf ' '
  while sleep 1; do
    printf '\b%.1s' "$sp"
    sp=${sp#?}${sp%???}
  done
}
}}}

One way to use these spinners in a script is to run them as background processes, and kill them when you're done.  For example,

{{{
# POSIX sh
spin & spinpid=$!
# long-running commands here
kill "$spinpid"
}}}

If you already have a loop which does a lot of work, you can write a function that "advances" the spinner one step at a time, and call it at the beginning of each iteration:

{{{
# Bash
sp='/-\|'
sc=0
sn=${#sp}
spin() {
    printf '\b%s' "${sp:sc++%sn:1}"
}
endspin() {
    printf '\r%s\n' "$*"
}

until work_done; do
   spin
   some_work ...
done
endspin
}}}

A similar technique can be used to build [[BashFAQ/044|progress bars]].

----
CategoryShell