Differences between revisions 13 and 14
Revision 13 as of 2017-03-31 05:46:23
Size: 1318
Editor: r180-216-10-159
Comment:
Revision 14 as of 2020-04-04 01:37:26
Size: 1692
Editor: GreyCat
Comment: mark examples by requirements, make the POSIX one really POSIX, make them functions, and show how to call them
Deletions are marked like this. Additions are marked like this.
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i=0
sp='/-\|'
n=${#sp}
printf ' '
sleep 0.1
while true; do
# Bash, with GNU sleep
spin() {
  local
i=0
  local sp='/-\|'
  local n=${#sp}
  printf ' '
  sleep 0.1
  while true; do
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done   done
}
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sp='/-\|'
printf ' '
sleep 0.1
while true; do
# POSIX sh
spin() {
  
sp='/-\|'
  printf ' '
  sleep 1
  while true; do
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    sleep 0.1
done
    sleep 1
  done
}
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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: 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,
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# 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, with GNU sleep
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    printf '\r%s\n' "$@"     printf '\r%s\n' "$*"
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Can I do a spinner in Bash?

Sure!

# Bash, with GNU sleep
spin() {
  local i=0
  local sp='/-\|'
  local 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:

# POSIX sh
spin() {
  sp='/-\|'
  printf ' '
  sleep 1
  while true; do
    printf '\b%.1s' "$sp"
    sp=${sp#?}${sp%???}
    sleep 1
  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, with GNU sleep
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

BashFAQ/034 (last edited 2020-04-04 01:37:26 by GreyCat)