[SOLVED] Bash command execution produces unwanted newline output

Issue

Ordinarily, running a command as $(command) discards any trailing newlines produced by command. However, when I run this command:

output=$(kcadm get users)

I always get a newline echoed. Why, and how can I get rid of it? It doesn't make any difference if I do this, or an equivalent:

output=$(kcadm get users) > /dev/null 2>&1

kcadm is an alias to a shell script, which runs Java and produces JSON output. If I run the script directly, I can always completely suppress any output from it (kcadm get users > /dev/null 2>&1), but I of course need to record the output for analysis.

EDIT

Before anyone else jumps in with a close vote, please: the bash manual says that "trailing newlines are deleted" in $() command substitution. The suggested answer is not, AFAICT, relevant.

YET ANOTHER EDIT

The suggested answer is for an entirely different question, and simply handles obvious cases where a substitution on the output removes a newline. This question is about a situation where the newline shouldn't have happened in the first place, and what caused it. This really should have been obvious to the close voters.

Solution

Assumptions:

• when OP says I always get a newline echoed, this is in reference to the output from output=$(kcadm get users) and not the result of echo "$output"

Without more debugging details I'm going to guess that kcadm is sending a single blank line to stderr.

If this is the case then the stderr output is not captured by OP's current command - output=$(kcadm get users) - but rather passed to the terminal.

A simple test/fix would be to redirect kcadm's stderr to stdout, eg:

output=$(kcadm get users 2>&1)

Answered By - markp-fuso

Answer Checked By - Timothy Miller (WPSolving Admin)