├── README.md
├── showing-file-download-progress-using-wget
    └── demo.sh
└── showing-progress-with-a-bash-spinner
    ├── README.md
    └── demo.sh


/README.md:
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1 | Bash Tips and Tricks
2 | ====================
3 | 
4 | An archive of the tips and tricks I share on my blog.
5 | 


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/showing-file-download-progress-using-wget/demo.sh:
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 1 | #!/usr/bin/env bash
 2 | 
 3 | download()
 4 | {
 5 |     local url=$1
 6 |     echo -n "    "
 7 |     wget --progress=dot $url 2>&1 | \
 8 |         grep --line-buffered "%" | \
 9 |         sed -u -e "s,\.,,g" | \
10 |         awk '{printf("\b\b\b\b%4s", $2)}'
11 |     echo -ne "\b\b\b\b"
12 |     echo " DONE"
13 | }
14 | 
15 | file="patch-2.6.37.gz"
16 | echo -n "Downloading $file:"
17 | download "http://www.kernel.org/pub/linux/kernel/v2.6/$file"
18 | 


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/showing-progress-with-a-bash-spinner/README.md:
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 1 | I've [mentioned before][wget] that I like to show users of my scripts useful
 2 | information. This can be a complex progress bar, a simple progress meter, or
 3 | it can be an animation to let the user know the script hasn't hung. These
 4 | animations are typically called [Throbbers][throbber] are exist purely to tell
 5 | the user to continue patiently waiting. Sometimes folks, like met, call
 6 | Throbbers Spinners for two reasons. First, a very common throbber animation
 7 | type is the spinning wheel. Second, the word throbber sounds oddly sexual, and
 8 | sort of creeps me out if I say it too many times in a sentence (Just kidding.
 9 | Well, no, not really.)
10 | 
11 | This tip will show you to create a spinner for your Bash scripts. If you have
12 | a long running process and don't want to try to tell the user approximately
13 | how much of that process is left to run, showing them a spinner is a great
14 | alternative.
15 | 
16 | ### Implementing the Spinner
17 | 
18 | The throbber, er I mean spinner, is implemented as a loop that shifts a string
19 | during each iteration.
20 | 
21 |     spinner()
22 |     {
23 |         local pid=$1
24 |         local delay=0.75
25 |         local spinstr='|/-\'
26 |         echo "$pid" > "/tmp/.spinner.pid"
27 |         while [ "$(ps a | awk '{print $1}' | grep $pid)" ]; do
28 |             local temp=${spinstr#?}
29 |             printf " [%c]  " "$spinstr"
30 |             local spinstr=$temp${spinstr%"$temp"}
31 |             sleep $delay
32 |             printf "\b\b\b\b\b\b"
33 |         done
34 |         printf "    \b\b\b\b"
35 |     }
36 | 
37 | Let's examine the meat of the tip. First, I remove the first character from
38 | the string and save the remaining characters into a `temp`.
39 | 
40 |             local temp=${spinstr#?}
41 | 
42 | Then I use `printf` to output the first character of `spinstr`, which contains
43 | our animation.
44 | 
45 |             printf " [%c]  " "$spinstr"
46 | 
47 | Finally, I shift `spinstr` by constructing a new string that contains the
48 | value of `temp` and all characters from `spinstr` that aren't in `temp`.
49 | 
50 |             local spinstr=$temp${spinstr%"$temp"}
51 | 
52 | ![Bash Spinner Steps 1 and 2][step12]
53 | ![Bash Spinner Steps 1 and 2][step34]
54 | 
55 | ### How it Works
56 | 
57 | When you have a task to run that will take a large (or unknown) amount of time
58 | invoke it in a background subshell like this:
59 | 
60 |     (a_long_running_task) &
61 | 
62 | Then, immediately following that invocation, call the spinner and pass it the
63 | PID of the subshell you invoked.
64 | 
65 |     spinner $!
66 | 
67 | The `$!` is a [bash internal variable][internal-variable] for the PID of the
68 | last job run in the background. In this case, it will give us the PID of the
69 | bash shell executing our long running task.
70 | 
71 | 
72 | ### An Example
73 | 
74 | 
75 | [internal-variable]: http://tldp.org/LDP/abs/html/internalvariables.html "Bash Internal Variables"
76 | [wget]: /showing-file-download-progress-using-wget.html "Showing File Download Progress using Wget"
77 | [throbber]: http://en.wikipedia.org/wiki/Throbber "Throbbers"
78 | ![step12]: /wp-content/uploads/2011/02/bash-spinner-step12.png "Bash Spinner Steps 1 and 2"
79 | ![step34]: /wp-content/uploads/2011/02/bash-spinner-step34.png "Bash Spinner Steps 3 and 4"
80 | 


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/showing-progress-with-a-bash-spinner/demo.sh:
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 1 | spinner()
 2 | {
 3 |     local pid=$1
 4 |     local delay=0.75
 5 |     local spinstr='|/-\'
 6 |     while [ "$(ps a | awk '{print $1}' | grep $pid)" ]; do
 7 |         local temp=${spinstr#?}
 8 |         printf " [%c]  " "$spinstr"
 9 |         local spinstr=$temp${spinstr%"$temp"}
10 |         sleep $delay
11 |         printf "\b\b\b\b\b\b"
12 |     done
13 |     printf "    \b\b\b\b"
14 | }
15 | 
16 | (sleep 10) &
17 | echo -n "Doing something really important, please wait... "
18 | spinner $!
19 | echo " DONE"
20 | 


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