CODEWITHSUNDEEP
bashshell
user3495562
user3495562

Reputation: 335

input from terminal <<<?

I saw the code written for testing our code with input from termial:

./spellcheck corpus_colors <<< rend

corpus_colors is the filename, I guess rend is for terminal input.

<<< behaves as terminal input?

Upvotes: 1

Views: 196

Answers (3)

Charles Duffy
Charles Duffy

Reputation: 295443

<<< is a bash extension (not available in baseline POSIX shells) which redirects literal content to stdin (with an added trailing newline). It is implementation-defined whether it appears to be a pipeline or a temporary file. It does not act as a terminal -- that is to say, isatty() will fail.

Compared to

echo rend | ./spellcheck corpus_colors

...using

./spellcheck corpus_colors <<<rend

can be slightly more efficient, avoiding the extra subshell needed to set up a pipeline. Avoiding this subshell also means that an operation can be a shell function which changes shell state, and these state changes can persist past the end of the function's execution.

See the wikipedia article on "here strings", or (better) the relevant component of the bash manual.

Upvotes: 5

bsoist
bsoist

Reputation: 785

You can use certain characters to redirect both input and output.

Examples ...

./someprogram > foo.txt

Will replace the file foo.txt ( or create it ) and add the standard output of someprogram

./someprogram >> foo.txt

Will append the standard output of someprogram to the file foo.txt ( creating it if necessary ) 

./someprogram < foo.txt

Will use the contents of foo.txt as standard input for someprogram

./someprogram | someotherprogram

Will redirect the standard output of someprogram and use it as the standard input for someotherprogram

./someprogram < foo.txt > bar.txt

Will use the contents of foo.txt and the standard input of someprogram and redirect the standard output of someprogram to the file bar.txt

./someprogram <<< rends

Will use "rends\n" ( without the quotes ) as standard input for someprogram

This page has some good information on that topic.

Upvotes: 2

Gargan
Gargan

Reputation: 21

Under BASH <<< is used to specify a 'Here String'. It's an inline version of a 'Here Document'. What ever comes after <<< is fed into stdin of the calling program. It is similar to echoing through a pipe to a command. More information can be found here: http://tldp.org/LDP/abs/html/x17837.html

Upvotes: 2

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