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How Unix programmers at restaurants search menus for their favorite plate

miguelmota profile image Miguel Mota ・2 min read

A Unix programmer heads over to the local diner to get something to eat for lunch. He, or Bob as he prefers, knows better than to manually scan the entire menu with his eyeballs because it's inefficient. Bob knows that there's a better way to automate the process in searching for what he wants to eat.

Last time he was here he had a pretty good pasta-and-shrimp plate for under 10 bucks.

Bob wonder's if this same dish is still available. He pops open his laptop running Linux and scrapes the restaurant website menu table into a plain text file.

menu.txt

the menu

steak burrito $11.95
pasta and shrimp $9.75
caesar salad $6.50

Now that Bob has the menu, he does a grep search for the pasta-and-shrimp plate:

$ cat menu.txt | grep shrimp

pasta and shrimp $9.75

So far so good. He filters for the price column by using awk and the NF variable (which is the number of columns fields available) in order to get the last column containing the prices:

$ cat menu.txt | grep shrimp | awk '{print $NF}'

$9.75

The starvation is kicking in and he's typing furiously by now. Bob proceeds with sed to turn the dollar amount into an integer by replacing everything except for what's inbetween the dollar symbol and decimal period. He'll use a capturing group and replace the contents with the first capture group \1:

$ cat menu.txt | grep shrimp | awk '{print $NF}' | sed -E 's/\$([0-9]+)\..*/\1/g'

9

Finally, using the handy test command and the less-than flag -lt, Bob can check whether the price is less than 10 with the help of xargs to pipe the value as the first argument to test:

$ cat menu.txt | grep shrimp | awk '{print $NF}' | sed -E 's/\$([0-9]+)\..*/\1/g' | xargs -I {} test {} -lt 10 

But wait there's no output! Actually, test returns an exit status code of 0 if the condition passes or 1 if no match.

Bob simply echo's Available if the previous command was successful by using &&, otherwise he'll echo :( by using the double pipe || if it was not successful:

$ cat menu.txt | grep shrimp | awk '{print $NF}' | sed -E 's/\$([0-9]+)\..*/\1/g' | xargs -I {} test {} -lt 10 && echo 'Available!' || echo ':('

Available!

Voila! there it is, the desired pasta-and-shrimp plate is still the under ten bucks. Bob is happy and proceeds to order his favorite dish.

(hope you liked this intro post to unix pipes and bash commands!)

Discussion

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tomislacker profile image
Ben Tomasik

What sort of monster does cat | grep !?

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acidnik profile image
acidnik

With real life menus with millions of lines, you usually start with head | grep, and then, when you one-liner of 15 lines is complete, you replace head with cat and cross your fingers

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jeshan profile image
Jeshan Giovanni BABOOA

real life menus with millions each? ;)

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acidnik profile image
acidnik

That was my attempt to make a joke

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blackknight36 profile image
Michael

You can almost accomplish this entire task using awk. For example:

awk -F '$' '/shrimp/ {printf "%s- %.2f\n", $1, $NF}' < menu.txt

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chiefnoah profile image
Noah Pederson

But then you have to use awk 🤮

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Christopher McClellan

awk is Turing Complete.
s/almost//

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jgomo3 profile image
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Pulkit Singhania

Grep won't be able to find anything because you are searching for ! Which is not in the menu

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moopet profile image
Ben Sinclair

I've been reading the thread about this on /r/programming (how circular!) and they're mostly (deliberately?) missing the point and trying to optimise it rather than to see it as a demonstration of pipes.

cough

grep -q 'shrimp.*$[0-9]\.' menu.txt && echo "Available" || echo ":("

EDIT: changed \d shortcode for [0-9] so it'll work with BSD and GNU grep.

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Ken Bellows

That's what this bit at the end is for:

$[0-9]\.

That bit of the regex will only match on a line that contains a dollar sign ($), a single digit ([0-9]), and a literal dot (\.). So "$2.99" will match, but "$12.99" won't, because there are two digits between the dollar sign and the dot.

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moopet profile image
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moopet profile image
Ben Sinclair

| rev | cut -d\ -f1 | rev

troll face

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catchenal profile image
Cat Chenal

Given this menu:

ps1$cat menu.txt

the menu

steak burrito $11.95
pasta and shrimp $9.75
caesar salad $6.50
shrimp salad $9.99
alfredo shrimp $10

My Nix programmer does this:

awk -F$ '/shrimp/{if ($NF < 10){ print $1}}' menu.txt

pasta and shrimp
shrimp salad

awk rules!

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labibllaca profile image
labibllaca

if you are looking for meals under 10 bucks, as shown in ($NF < 10), why isn't caesar salad($6.50) in the output ?

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hoffmann profile image
Peter Hoffmann

Why are you guys alwas using awk for field separation? There ist cut -d" " -f3 that is nice as well

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Jesús Gómez

"test returns an exit status code of 1 if the condition passes or 0 if no match." It is actually backwards: reddit.com/r/programming/comments/...

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Peter Bertok

The equivalent is much more readable with PowerShell:

$shrimp = Get-Content menu.txt | Select-String 'shrimp'
$price = $shrimp | ForEach-Object { $cols = $_ -split ' '; $cols[-1] }
$under10 = [decimal]$price.Substring(1) -lt 10
if ( $under10 ) { 'Available!' } else { ':(' }

Of course, you can use aliases to make this a bit "shorter", but then we're back in the world of Unix, where precious bytes have to be saved to achieve acceptable performance on 300 baud Teletype terminals:

$p = gc menu.txt | sls 'shrimp' | % { $c = $_ -split ' '; $c[-1] }
if ([decimal]$p.Substring(1) -lt 10) {'Available!'} else {':('}

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Agustin Navcevich

This is why two unix programmers will never eat together, because they will start to discuss which is the best way to order the shrimps

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Mohamed Shoukry

Bob should've rounded up. He probably ran off when he remembered he didn't factor taxes in!
Oh & btw, he should've done a case insensitive grep grep -i shrimp menu.txt. Although if he's using awk anyway, then he might have included that there too and avoid all those unnecessary pipes! awk '$0~/shrimp/{print $NF}

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ppetermann profile image
ppetermann

In a lot of countries the tax is part of the price

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GManon

Hilarious!

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chbarts profile image
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Swarup Kumar Mahapatra

This article is awesome. It really shows all the possibilities in Linux. I am quite surprised by the comments here where people are trying to correct you. Anyways, good job

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Jeff Prestes

hahaha, it's amazing! Congratulations.

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blackknight36 profile image
Michael

You need to replace your double quotes with literal single quotes. Here's why.

$ echo "Available!"
bash: !": event not found

$ echo 'Available!'
Available!

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slamotte profile image
Steve

I don't like how there's no code for how to scrape the website into menu. txt. Incomplete solution! ;-)

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pawail profile image
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Rick Cloud

Or, he could merely 'read' visually the menu??? Didn't realize this was a lesson in Unix coding until the end... :-) Laugh at me...

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tameware

It took me a while to realize that the price is truncated to an integer only because 'test' can't handle decimals. That might deserve a mention.

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blackknight36 profile image
Michael

Useless use of cat detected.

porkmail.org/era/unix/award.html