Diff for "BashFAQ/034"

Differences between revisions 2 and 14 (spanning 12 versions)

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

-  ⇤ ← Revision 2 as of 2008-05-09 11:14:31 → 
  Size: 1136
  Editor: Lhunath
  Comment: echo -ne -> printf; explain the code a little.  add an example loop for the function that is to be called within a loop.
+   ← 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.
 Line 1:
-[[Anchor(faq34)]]
+<<Anchor(faq34)>>
 Line 3:
-Sure.
+Sure!
-Line 5:
+Line 6:
-    i=1
    sp="/-\|"
    echo -n ' '
    while true
    do
        printf "\b${sp:i++%${#sp}:1}"
    done
+# 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
}
-Line 14:
+Line 20:
-The theory here is that each time the loop iterates, it displays the next character in the `sp` string, wrapping around as it reaches the end (where `i` is the position of the current character to display and `${#sp}` is the length of the `sp` string).
+Each time the loop iterates, it displays the next character in the `sp` string, wrapping around as it reaches the end.  (`i` is the position of the current character to display and `${#sp}` is the [[BashFAQ/007|length]] of the `sp` string).
-Line 18:
+Line 24:
-If you want it to slow down, put a {{{sleep}}} command inside the loop (after the printf).
+To slow it down, the `sleep` command is included inside the loop (after the `printf`).
-Line 20:
+Line 26:
-If you already have a loop which does a lot of work, you can call the following function at the beginning of each iteration in that loop to update the spinner every time an iteration of your loop begins:
+A POSIX equivalent would be:
-Line 22:
+Line 29:
-sp="/-\|"
+# 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='/-\|'
-Line 25:
+Line 58:
-   printf "\b${sp:sc++:1}"
   ((sc==4)) && sc=0
+    printf "\b${sp:sc++:1}"
    ((sc==${#sp})) && sc=0
    sleep 0.1
-Line 29:
+Line 63:
-   printf "\r%s\n" "$@"
+    printf '\r%s\n' "$*"
    sleep 0.1
-Line 34:
+Line 69:
-   some_work
+   some_work ...
-Line 40:
+Line 74:
-A similar technique can be used to build progress bars.
+A similar technique can be used to build [[BashFAQ/044|progress bars]].

----
CategoryShell