How to print new lines at the end of functions?

Question

If I type echo hello, my terminal looks like this:

My-Computer:~ user$ echo hello
hello
My-Computer:~ user$ 

But if I have a function like this

stringen () { cat /dev/urandom | env LC_CTYPE=C tr -cd 'a-Z-A-z-0-9' | head -c "$1" ; }

It looks like this

My-Computer:~ user$ stringen 18
^\k6JPWVIUdEiudcWSMy-Computer:~ user$ 

See that it doesn't print it in a new line? Same thing when using printf vs echo. How can I do so that my functions makes new lines like this? I thought that the ; would take care of this but obviously not.

For example, this returns what I want

variable=$(stringen 18)
echo $variable

Is it something with echo?

Answer 1

Neither, cat, tr or head adds a newline character (urandom could, but it's random so I wouldn't trust it). You have to manually insert the new line, with either a printf '\n' at the end of your function, or an echo.

BTW, some shells do add it, like zsh, to prevent these kinds of situations.

Answer 2

It doesn't matter in the least if your function prints a newline or not. Command substitution will remove them if there are any present.

Bash performs the expansion by executing command and replacing the command substitution with the standard output of the command, with any trailing newlines deleted. (emphasis mine)

testfunc() { echo hello; }    # a newline is printed
output=$(testfunc)            # $output does NOT contain a trailing newline
echo "$output"                # echo adds a newline
printf "%s" "$output"         # no newline

Answer 3

IMHO, this might partly have to do with echo but there's another part of the problem taking influence. So the ideal situation would be if your distro did ship a recent GNU version of tr (like in mine), because as you can see below, there is a clear quirk in your syntax and GNU tr complains to show you where you have to apply the "fix".

original:

$ stringen() { cat /dev/urandom | env LC_CTYPE=C tr -cd 'a-Z-A-z-0-9' | head -c "$1" ; }

$ stringen 18
tr: range-endpoints of 'a-Z' are in reverse collating sequence order

Ouch! Here is an alternate version of your line which fixes it (at least in my distro with GNU tr it did the trick):

"fixed":

$ stringen () { cat /dev/urandom | env LC_CTYPE=C tr -cd 'A-Za-z0-9' | head -c "$1" ; }
$ stringen 18
V068BrYGKIICyLI4QB
$ 

Conclusion: you had better not mix sets with tr, but when combining sets/ranges, always make sure that you keep big letters to big letters and small letters to small letters.

However: With a non-GNU tr, the problem with the missing newline might be still persisting. But with a GNU one, my corrected line will no longer make any fancy newline trickery necessary.

Answer 4

You don't need a variable to save the output for this. Simply echo the output directly :

echo "$(stringen 18)"