Bash script

hounslow · 11-23-2015, 10:45 PM

I am new to Linux and programming in general. I was wondering if anyone would be willing to show me how to write a script to convert miles per hour to feet per second.

astrogeek · 11-23-2015, 11:22 PM

Welcome to LQ!

Just think about the problem logically...

1. Write down the math equation which includes the input variable (mph) and produces the output value (fps).
2. Learn how to use the facilities of your favored scripting language to express that equation.
3. Put in the input value (mph), run the script and get the output value.

So first, since this is a simple units conversion the math will look something like this...

Code:

FPS = k X MPH
   where k is a proportionality constant - the math is left to you...

So it really involves a single multiplication operation.

In a shell script multiplication is indicated by a * character.

Variable values are assigned by simply setting a name equal to a value.

Writing something to the output is very easy.

So, overall a simple script might be something like this...

Code:

#!/bin/bash

MPH=60
k=enter the value from the math...
FPS=0

#Now do the math in terms recognized by the shell (it will require some context characters not shown here)..

FPS=k*MPH

#And write the results out here... you'll figure out how easily enough!

You can find the missing pieces here, Bash Beginners Guide. See if you can put it all together and let us know if you get stuck!

Good luck!

grail · 11-24-2015, 01:41 PM

The only thing I would add to the above is that by default bash will not calculate decimal numbers, so you either need to use a helper, such as bc, or perform calculations to shift the decimal point
whilst working out your answers.

Of course you also have the ability to use other languages such as Perl or Python

Good luck

Habitual · 11-24-2015, 02:30 PM

Quote:

Originally Posted by hounslow

I am new to Linux and programming in general. I was wondering if anyone would be willing to show me how to write a script to convert miles per hour to feet per second.

This is not something that a beginner programmer will be able to do without "severe motivation", so here's some motivation:

Code:

#!/bin/bash 
# traveltime - a program to calculate how long it will
# take to travel a fixed distance 
# syntax: traveltime miles mph 

X60=$(($1 * 60)) 
TOTMINUTES=$(($X60 / $2)) 
HOURS=$(($TOTMINUTES / 60)) 
MINUTES=$(($TOTMINUTES % 60)) 
echo "The trip will take $HOURS hours and $MINUTES minutes"

usage: script <distance> <speed>

Actual usage:

Code:

sh travel 100 60

The trip will take 1 hours and 40 minutes

That should get you started.

References:
http://www.tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html
http://www.tldp.org/LDP/Bash-Beginne...tml/index.html
http://tldp.org/LDP/abs/abs-guide.pdf
http://www.tldp.org/LDP/abs/html/
http://mywiki.wooledge.org/BashFAQ
http://mywiki.wooledge.org/BashPitfalls

rtmistler · 11-30-2015, 09:47 AM

To add to the suggestions above, I have some links in my signature for BASH programming, one of them is a blog entry with suggestions as to how to write and debug BASH scripts. I wrote it a long time ago and probably should update it, but the methodologies are still the same regarding how to debug and things to do to assist yourself in accomplishing your goal.

The most common suggestion is to add a line to your script after the #!/bin/sh line at the top of the script:

Code:

set -xv

What this does is enables debug so that when you run your script it shows detailed output about variable assignments, tests their results, and the line numbers as well as statements being executed.

joel2001k · 12-11-2015, 01:23 PM

http://www.tldp.org/LDP/abs/html/