I am trying to streamline a README, where I can easily pass commands and their outputs to a document. This step seems harder than I thought it would be.
I am trying to pass the input and output to a file, but everything I am trying just either displays echo test or test
The latest iteration, which is becoming absurd is:
echo test | xargs echo '#' | cat <(echo) <(cat -) just shows # test
I would like the results to be:
echo test
# test
You can make a bash function to demonstrate a command and its output like this:
democommand() {
printf '#'
printf ' %q' "$@"
printf '\n'
"$@"
}
This prints "#", then each argument the function was passed (i.e. the command and its arguments) with a space before each one (and the %q makes it quote/escape them as needed), then a newline, and then finally it runs all of its arguments as a command. Here's an example:
$ democommand echo test
# echo test
$ democommand ls
# ls
Desktop Downloads Movies Pictures Sites
Documents Library Music Public
Now, as for why your command didn't work... well, I'm not clear what you thought it was doing, but here's what it's actually doing:
echo test, simply prints the string "test" to its standard output, which is piped to the next command in the chain.takes its input ("test") and adds it to the command it's given (echo '#') as additional arguments. Essentially, it executes the commandecho '#' test`. This outputs "# test" to the next command in the chain.cat <(echo) <(cat -) is rather complicated, so let's break it down:
echo prints a blank linecat - simply copies its input (which is at this point in the pipeline is still coming from the output of the xargs command, i.e. "# test").cat <(echo) <(cat -) takes the output of those two <() commands and concatenates them together, resulting in a blank line followed by "# test".
Pass the command as a literal string so that you can both print and evaluate it:
doc() { printf '$ %s\n%s\n' "$1" "$(eval "$1")"; }
Running:
doc 'echo foo | tr f c' > myfile
Will make myfile contain:
$ echo foo | tr f c
coo
