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Using bash inline "here document" with three less-than symbols on command line

Terminal - Using bash inline "here document" with three less-than symbols on command line
<<<"k=1024; m=k*k; g=k*m; g" bc
2009-06-17 10:35:10
User: mpb
8
Using bash inline "here document" with three less-than symbols on command line

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.

Alternatives

There is 1 alternative - vote for the best!

Terminal - Alternatives
command <<< word
2012-02-29 03:14:54
User: adeverteuil
Functions: command
Tags: bash stdin
11

Don't do this:

echo word | command

Using a bash "here strings" and "here documents" look leeter than piping echo into the command. Also prevents subshell execution. Word is also expanded as usual.

Know a better way?

If you can do better, submit your command here.

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).

Comment by inof 309 weeks and 4 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.

Comment by mpb 309 weeks and 3 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).

Comment by mpb 309 weeks and 3 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!

Comment by chriszuma 173 weeks and 6 days 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.

Comment by bobnewstadt 166 weeks and 2 days ago

Your point of view

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