The 'here string' ( | md5sum or printf ... | md5sum instead. But my question specifically pertains to the 'here string'.

It seemed to me that the end of a here string is newline. I realize I am wrong: $ cat <<< hello world cat: world: No such file or directory What can signify the end of a here string?

I have a variable foo_var which contains ASCII text (base64 text, with some additional text which includes dashes, spaces, and underscores). I write this var to a file as follows: cat foo_file I have a program which reads from stdin (openssl). This invocation works, with an exit code of 0: $ openssl rsa -passin stdin -pubout < foo_file but both these fail, with a message saying that stdin can't be read, and an exit code of 1: $ openssl rsa -passin stdin -pubout <<<"$foo_var" $ echo "$foo_var" | openssl -passin stdin -pubout What's the difference between these cases? The obvious answer is that parameter expansion occurred in the failing case, but this can't be right, because the same parameter expansion would have happened when foo_file was created. I'm on bash 5.1.16. *EDIT* Added the args, as requested. However, there's a complication - the args ask for both a password and a private key on stdin. This relies on what seems to be an undocumented openssl feature, which is that a single input stream can be used for both, but the password must be on the first line, followed by the key. So, it's not trivial to repeat. If anyone really wants a go I'll post a working password/key file. *EDIT2* I've done some debug by running under strace. For both the working and failing cases, there's some (essentially identical) initial setup, and then a read request is made on stdin, for 4K bytes. This returns 1887 (the number of bytes actually available), and therefore advances the file position to 1887. In both cases, openssl then attempts an lseek (lseek 0, -1875, SEEK_CUR)). For the failing case, this fails with an ESPIPE, as you might expect, and the program terminates soon after. For the passing case (redirection from an actual file) lseek succeeds, returning a new file position of 12. Ok, so nobody expects stdin to be seekable. But bash sets up everything in both cases, and in both cases openssl sees only stdin. It can seek in one case and not the other. But openssl knows that the input is stdin, because that's a command-line parameter, so why does it seek at all?? Conclusion? (A) Input redirection from a file and a here string are *not* equivalent, because Linux somehow makes seeking possible in the first case, or (B) openssl has messed up by attempting the lseek, and is taking advantage of a bug/feature? In any event, it should never have attempted the lseek, because it already knew what the data was.

I have this command to run a checksum in some software I want to install: echo "85762db0edc00ce19a2cd5496d1627903e6198ad850bbbdefb2ceaa46bd20cbd install.sh" | sha256sum -c But I would like to use it with the sha256sum command *first*. So we have that using heredoc: sha256sum -c << EOF 85762db0edc00ce19a2cd5496d1627903e6198ad850bbbdefb2ceaa46bd20cbd install.sh EOF But now I would like this to be all on one line... So I tried: sha256sum -c << EOF ; 85762db0edc00ce19a2cd5496d1627903e6198ad850bbbdefb2ceaa46bd20cbd install.sh ; EOF And it doesn't work. But _shouldn't_ it work if the semicolon ; means "we're going to run another command"? Can we get it in that order, but written a different way to work on one line? If not, why can't we tell it what to do on each multiple line, but on one line?

If I run:

IFS=':' cat <<< $(echo $PATH)

then the ":" are used for word splitting and the output contains spaces instead of ":", but if I run:

echo $PATH | IFS=':' cat

they are not. My understanding of pipes a | b is that they connect fd 1 of a to fd 0 of b. And my understanding of herestrings a <<< string is that they write the string directly to fd 0 of a. In either case it seems like the same thing should be written to fd 0 of cat. That suggests that there should be no difference between the two commands, but clearly there must be something I've misunderstood because this shows a diff:

diff <(echo $PATH | IFS=':' cat) <(IFS=':' cat <<< $(echo $PATH))

I am not trying to accomplish something and asking for some text I can cut and paste to do it. I have described a situation that contradicts my understanding and have asked for an explanation as to what I have misunderstood. Can someone explain why these two commands produce different output? ---- I just tried this on bash 4 and do not get a difference there. That's why I asked "What version of Bash are you on"... So, I've edited the question to limit it to bash 3. I am not asking about bash 4. Again, the question is not "can someone please give me something I can cut and paste to do a thing without thinking about it". The question is "what is the difference between these two things".

Here is what I am trying to do: docker exec -it $1 /bin/bash <<< $CONTAINER_ID But this doesn't work: Output: "docker exec" requires at least 2 arguments. It seems that <<< completely replaces STDIN ignoring $1. Is it possible to replace only one argument with <<