Bash Scripting on Linux (The Complete Guide) Class 04 - Basic Math
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- Опубликовано: 2 июн 2024
- Performing math operations in Bash is a bit different than on other platforms, so it may prevent some future confusion if you learn about these things now. And why not? This tutorial is only six minutes long and there's plenty of worse things you can spend your time on, so check out this Bash tutorial and learn how to perform basic math functions!
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Individual Sections
00:00 - Intro
01:00 - Math is handled differently in Bash
01:28 - The "evaluate expression" command (expr) in Bash
02:37 - Multiplication in Bash (and how to use an escape symbol)
03:48 - Using variables with math expressions
OTHER BASH SCRIPTING SERIES EPISODES
- Class 01 ➜ Introduction: linux.video/bash1
- Class 02 ➜ Hello World: linux.video/bash2
- Class 03 ➜ Variables: linux.video/bash3
- Class 04 ➜ Math Functions: linux.video/bash4
- Class 05 ➜ If Statements: linux.video/bash5
- Class 06 ➜ Exit Codes: linux.video/bash6
- Class 07 ➜ While Loops: linux.video/bash7
- Class 08 ➜ Universal Update Script: linux.video/bash8
- Class 09 ➜ For Loops: linux.video/bash9
- Class 10 ➜ Where To Store Your Scripts: linux.video/bash10
- Class 11 ➜ Data Streams: linux.video/bash11
- Class 12 ➜ Functions: linux.video/bash12
- Class 13 ➜ Case Statements: linux.video/bash13
- Class 14 ➜ Scheduling Jobs (Part 1): linux.video/bash14
- Class 15 ➜ Scheduling Jobs (Part 2): linux.video/bash15
- Class 16 ➜ Arguments: linux.video/bash16
- Class 17 ➜ Building a Backup Script: linux.video/bash17
- Class 18 ➜ Closing: linux.video/bash18
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"expr" is good to know, but on a modern system, you should be using "$(( ))" for numeric calculations. E.g. $((a + b)). Also, for multiplication you can simply do $((10 * 10)), not needing a double asterisk or escape character.
You literally just helped me fix a script I was writing to convert GPU temps from C to F. Thanks! 👍🏻
i am looking for partner who want to learn bash through co opearation
If I do it this way, it performs that calculation, but it is also treating it as a command
@@VitaDani314 same. Got to echo it first.
thks bro
@@imnottellingyoumyname3050
I hope your business keeps growing. I appreciate you man.
Hello from Athens Greece, I watch your channel and I suggest it to all new people that afraid of using Linux OS.
Thank you for your course, it is absolutely amazing that I can understand you the way you teach thank you !
I always love your mode of teaching, very simple, clear and straigth forward. Thanks.
Fun things to try:
echo {1..30}
echo {30..0}
thanks🙂
Oh, no! `expr` is deprecated - since 199x?
Use $((...)) in bash for simple integer calculations:
for op in + - \* / % ; do echo $((30 op 10)); done
40
20
300
3
0
Inside the double parens, you needn't mask the asterisk (here it needed to be masked for the for loop).
You needn't use $ to dereference value variables (I needed, because it was used for the operator
🐧> v=7
🐧> echo $((v + 4))
11
You may extend the math portfolio with exponentiation, often seen in shells as a^b, but here it is $((a**b)).
You may even perform bitwise OR, AND and XOR:
t530:~/dl 🐧> echo $((v | 4))
7
t530:~/dl 🐧> echo $((v & 4))
4
t530:~/dl 🐧> echo $((v ^ 4))
3
For floating point, you need of course, like viesic pointed out, bc (but not for +*/= and reasonable small values).
t530:~/dl 🐧> echo $((2**62))
4611686018427387904
t530:~/dl 🐧> echo "scale=314; 4*a(1);" | bc -l
3.141592653589793238462643383279502884197169399375105820974944592307\
81640628620899862803482534211706798214808651328230664709384460955058\
22317253594081284811174502841027019385211055596446229489549303819644\
28810975665933446128475648233786783165271201909145648566923460348610\
45432664821339360726024914127372458700660628
Do a performance comparision between `expr FOO` and `echo $((FOO))` in a loop which runs for 1s. On my system, the bash builtin `$((FOO))` is about 200x faster, than the external `expr FOO` call. Performance often doesn't matter, but there is no single advantage in using `expr` - well, maybe it is more portable for shells, which don't have `$((...))` or something similar.
Old versions of bash are still running around on the most unexpected places, and I agree with you that almost always $(()) is superior
@@AlbusRegis What do you mean by `old`? Do you think an intro to newbies should focus on teaching archaic syntax and styles?
In the file /usr/share/doc/bash/NEWS.gz, I find the news for version 2.0, following bash-1.14.7.(my current version is 5.1.16), stating (among other things):
t. The $[...] arithmetic expansion syntax is no longer supported, in
favor of $((...)).
Bash 2.0 seems to be from 2001. So most of its users are already dead. :)
Even the good, old `let` command is superior to `expr`, since it can perform ` let b=30**3; echo $b`
@@unbekannter_Nutzer I have found on the wild servers that sould be on a museum, running DOS era software because the big boss could not be bothered to update the program that "works perfectly fine". Unfortunately you have to be at least aware of deprecated stuff since it is out there and very much half alive.
@@AlbusRegis Well, I don't doubt that some old servers with outdated software is still in use, and for an experienced programmer, it is nice to know, how to handle them.
These videos are made in a technical satisfying way, well pronounced, fine equipment with a high, reliable frequency. Often I like to nit-pick on small issues, but here we see a lot of work wasted to the wrong audience. Who ever is already working as admin, supporting outdated machines, is a) very probably already trained b) in a small minority.
It's such a pity if beginners learn bad habits about math in the shell in such a beautiful way.
Wow Sir Nice . You have Brilliant Knowledge of Linux. I appreciate you Sir . I am Amit From India .
10/10 good passed short videos and perfect if someone come from any programming languages to make a reference
learned alot from your previous Vid and this as well. Thanks much
Great class!!!
I am learning many things from your video.
wish your good health
Great video Thank you
classic banger ma bro, short but good
Nice lecture
Thank you!
thanks jay
thank you!!
did not know the "expr" command. For mathematical calculations i`m using "bc" command, like that "echo 30 + 10 | bc"
I noticed that if you surround the * with quotation marks, that works as well
thnx!
!!!!*DOUBT*
whenever I create a variable in linux lets say 'myVar' it returns - myVar : command not found..... Can anyone pls tell the solution ??????
These math operations only seem to work with integers.
Does bash do order of operations
Great question.
Follow!
👍!
Will a division operation that doesn't reduce to an integer generate a float or maybe truncate the result to an integer? Will the expr command work at all with floats?
It truncates to nearest low integer: 8/3 will output 2 instead of rounding to 3.
My advice is that you should not trust bash to handle critical math, it makes good enough aproximations and works well with integers most of the time, but floating point or other number types are finicky at best
Edit:
expr errors with non integers:
expr 8.1 + 1
"expr: non integer argument"
@@AlbusRegis IMHO you can't say, it performs approximations. It's absolute accurate (hope so ;) ) in the range and scope of integer arithmetic, which means, it truncates, yes, predicable. 99/100 is zero and in many mature programming languages, if using int, too (C, Java, C++, ...).
expr 7234534365 \* 14734536 + 977
106597507044330617
(in the range up to 2^63-1).
But
expr 99 / 100 \* 100
will give you a result of 0, since it is evaluated left to right.
i am looking for partner who want to learn bash through co opearation
☯🙏
you can also use
echo $[100 + 30] # to give you 130