More Debt Watching from the Command Line

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Those of you who watch our Tech Tip Videos may have seen my video on how to fetch the US National Debt at the command line. The script contained here uses the idea I developed there and expands it to fetch the debt twice, with an optional pause in between, and then display the amount that the debt has increased during the pause.

You can use the script in the following fashion:

bash ndebt.sh 10
bash ndebt.sh 3:10
bash ndebt.sh 1:15:10

The argument to the script is the pause time, which can be given in seconds, or minutes:seconds, or hours:minutes:seconds. The script fetches the debt at the start, pauses for the requested amount of time, then fetches the debt again and prints out the amount the debt has increased.

For example, here we run the script and specify a time of 20 seconds:

$ bash ndebt.sh 20
During the last 20 seconds the US National Debt has increased by 901128.13

The script itself follows:

#!/bin/bash


# Check for pause time.
pause_time=0

if [[ "$1" ]]; then
	if   [[ $1 =~ ^([0-9]+):([0-9]+):([0-9]+)$ ]]; then
		pause_time=$(((${BASH_REMATCH[1]}*60*60) + (${BASH_REMATCH[2]}*60) + (${BASH_REMATCH[3]})))
	elif [[ $1 =~ ^([0-9]+):([0-9]+)$ ]]; then
		pause_time=$(((${BASH_REMATCH[1]}*60) + (${BASH_REMATCH[2]})))
	elif [[ $1 =~ ^([0-9]+)$ ]]; then
		pause_time=$1
	else
		echo "Bad pause time: $1" >&2
		exit 1
	fi
fi


# Get national debt.
function get_debt()
{
	local t=$(wget --quiet http://brillig.com/debt_clock -O - | grep debtiv.gif)

	t=$(sed -e 's/.*ALT="\$//' -e 's/".*//' -e 's/[ ,]//g' <<<$t)
	echo $t
}

# Print time item.
# Pass time value and one of 'hour', 'minute', 'ssecond'.
function fmt_time()
{
	local t=$1
	local p=$2
	if [[ $t -gt 0 ]]; then
		if [[ $t -eq 1 ]]; then
			printf '%d %s' $t $p
		else
			printf '%d %ss' $t $p
		fi
	fi
}

# Print the elapsed time between the first and second argument.
# Times given in seconds.
# Earliest time is first arugment.
function elapsed_time()
{
	local st=$1
	local et=$2
	local dt=$((et - st))
	local ds=$((dt % 60))
	local dm=$(((dt / 60) % 60))
	local dh=$((dt / 3600))
	
	echo $(fmt_time $dh 'hour') $(fmt_time $dm 'minute') $(fmt_time $ds 'second')
}


######################################################################

stime=$(date +%s)
sdebt=$(get_debt)

if [[ $pause_time -gt 0 ]]; then sleep $pause_time; fi

etime=$(date +%s)
edebt=$(get_debt)

t=$(elapsed_time $stime $etime)
d=$(bc <<<"scale=2; $edebt - $sdebt")

printf "During the last %s the US National Debt has increased by %s\n" "$t" "$d"


## vim: tabstop=4: shiftwidth=4: noexpandtab:
## kate: tab-width 4; indent-width 4; replace-tabs false;

The first part of the script uses bash's regular expression comparison operator (=~) to see if the passed argument is a valid time. Then come a few functions.

The first function, get_debt(), fetches the debt page from brillig.com and then extracts and cleans up the debt number. The debt number is extracted from the alt attribute of the image at the top of the page. The string there contains spaces and commas and a dollar sign, those are removed to give us a usable number.

The second function fmt_time() formats a time component for our output. For example, fmt_time 2 second prints "2 seconds", fmt_time 0 second prints "" (an empty string).

The third function, elapsed_time() takes two time values in seconds and calculates the difference between the two. It then formats the elapsed time in a readable fashion. For example elapsed_time 0 3659 prints "1 hour 59 seconds".

After that comes the main code. It records the start time, fetches the starting debt and then pauses. After the pause it records the end time and fetches the ending debt. Then bc is used to calculate the difference and the result is printed. Note that the time printed is the actual elapsed time and so it may be slightly different than the elapsed time you request on the command line, but usually only by a second or two.

AttachmentSize
ndebt.sh_.txt1.66 KB
______________________

Mitch Frazier is an Associate Editor for Linux Journal.

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bash version

Amos's picture

Mitch,
There is a discrepancy in my bash version:
[amos@localhost ~]$ bash --version
GNU bash, version 3.1.17(1)-release (i586-mandriva-linux-gnu)

Synaptics says my bash version is 3.1-8.

No It's OK

Mitch Frazier's picture

When the version number contains a -NUMBER that's a package release number, which is the number of times the package was built with the same version of the software. So, 3.1-8 means the package itself has been built 8 times with version 3.1 of bash. So, the "fuller" version, 3.1.17, is still version 3.1.

See the answer to the comment below as to how you can fix the script so it should run with that version of bash.

Mitch Frazier is an Associate Editor for Linux Journal.

Hi Mitch, I'm running PCLos

Anonymous's picture

Hi Mitch,
I'm running PCLos 2009.1 with bash 3.1.17
Amos

Quotes Needed with Bash 3.1

Mitch Frazier's picture

My system has bash 3.2. One of the improvements in version 3.2 was that you no longer needed to include quotes around regular expressions used with =~. Moreover, in version 3.2, regular expressions with quotes don't seem to work as you expect. Therefore, for 3.1 try adding quotes around the regular expressions in the =~ comparisons near the top of the file:

if   [[ $1 =~ '^([0-9]+):([0-9]+):([0-9]+)$' ]]; then
# ADD THESE   ^                            ^
...
elif [[ $1 =~ '^([0-9]+):([0-9]+)$' ]]; then
# ADD THESE   ^                   ^
...
elif [[ $1 =~ '^([0-9]+)$' ]]; then
# ADD THESE   ^          ^

Mitch Frazier is an Associate Editor for Linux Journal.

bash script

Amos's picture

Thanks a lot Mitch, it works perfectly.

National Debt Script

Anonymous's picture

I copied and pasted your script and then ran it. This is the error message I received:

[amos@localhost 0]$ ./natldebt.sh 10
./natldebt.sh: line 8: syntax error in conditional expression: unexpected token `('
./natldebt.sh: line 8: syntax error near `^(['
./natldebt.sh: line 8: ` if [[ $1 =~ ^([0-9]+):([0-9]+):([0-9]+)$ ]]; then'

Here's hoping it is my fault. I didn't check your script against the copied text.

Regards,
Amos

Bash Version

Mitch Frazier's picture

What version of bash do you have?

Mitch Frazier is an Associate Editor for Linux Journal.

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