CODEWITHSUNDEEP
linuxbashubuntu
Ousman
Ousman

Reputation: 11

Can cat command redirect input back to the stdin

I was reading through a bash script that takes an input and check if the there's a topic on the input word. At first, the list of available topics was created in the script from the lines of code below below.

    echo "On which topic do you want advice?"
    cat << topics
    politics
    startrek
    kernelnewbies
    sports
    bofh-excuses
    magic
    love
    literature
    drugs
    education
    topics

Based on my understanding, cat can take input from stdin or piping and redirect it to stdout

    cat
    now
    now
    later
    later

or redirect/append the input to a file content

    cat >> file.txt

Does cat take input from stdin an redirect it back to stdin? Also, why does topic have to appear twice in the first code block? Is it a wrapper or some sort of stdin copy/imitation?

I tried to see if there would be the file "topics" would be created in the directory, but there was nothing related to it existence or the input list of words in the working directory.

Upvotes: 0

Views: 222

Answers (1)

Diego Torres Milano
Diego Torres Milano

Reputation: 69208

what you see first is the echo from your terminal, when you press RETURN, cat receives the input you typed (stdin) and copies it to the output (stdout).

If you run

stty -echo; cat; stty echo

which disables local echo, runs cat (until EOF, usually ^D), and the re-enabled echo, you will see what you type only once.

Upvotes: 1

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