Using bash inline

<<<"k=1024; m=k*k; g=k*m; g" bc
There are two ways to use "here documents" with bash to fill stdin: The following example shows use with the "bc" command. a) Using a delimiter at the end of data: less-than less-than eeooff bc > k=1024 > m=k*k > g=k*m > g > eeooff 1073741824 b) using the "inline" verion with three less-than symbols: less-than less-than less-than "k=1024; m=k*k; g=k*m; g" bc 1073741824 One nice advantage of using the triple less-than version is that the command can easily be recalled from command line history and re-executed. PS: in this "description", I had to use the name "less-than" to represent the less-than symbol because the commandlinefu input text box seems to eat up the real less-than symbols. Odd.
Sample Output
$ # example 1: with the "bc" (basic calculator) command
$ <<<"k=1024; m=k*k; g=k*m; g" bc
1073741824

$ # example 2: with the "at" command
$ <<< "/home/mirror/cron_rsync_mandriva_updates" at now + 1 min
warning: commands will be executed using (in order) a) $SHELL b) login shell c) /bin/sh
job 66 at Sat Jun 20 11:33:00 2009


$ # example 3: calculating how long it takes for a signal across the Atlantic in fibre optic cable
$ # reference: https://en.wikipedia.org/wiki/Speed_of_light
$ # example 3, part 1: how fast does light travel in glass?
$ bc <<< "scale=4;  speedoflight=186282; speedoflight/1.5"    # light in glass travels at c / 1.5
124188.0000
$ # example 3, part 2: how many seconds for light to cross Atlantic in glass?
$ bc <<< "scale=4; ocean=3716; speedoflight=124188; ocean/speedoflight"
.0299

9
By: mpb
2009-06-17 10:35:10

1 Alternatives + Submit Alt

What Others Think

Why not simply use echo? echo "k=1024; m=k*k; g=k*m; g" | bc I think it's easier to understand, and it's more portable (works with any bourne shell, not just bash and zsh).
inof · 711 weeks and 6 days ago
@inof The point is to show the use of the " Sure, echo is an alternative but it means you have to use a pipe. I am here on commandlinefu to learn *new* things.
mpb · 711 weeks and 6 days ago
eh? that's odd: what happened to the three less-than symbols in my previous comment? Some odd character handing in the text input box for commandlinefu? It would also be nice to be able to edit comments (eg for spelling correctione etc).
mpb · 711 weeks and 6 days ago
What is the "three less-thans" operation actually called? I can't figure it out, and it's not in the TLDP guide!
chriszuma · 576 weeks and 1 day ago
The "three-less-thans" operator is called a Here String in the bash man page. See also chapter 19.1 of the Advanced Bash-Scripting Guide in the TLDP.
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Perfecthomepugs · 14 weeks ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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