How to store output from a remote host in a variable bash script

Question

I need to get all the wars on a remote tomcat server printed via my bash script. I am able to ssh on the remote server and execute the command to get wars with version :-

${SSH} ${DEST_USER}@${DESTHOST} "Command"

however if I am storing it in a variable I don't get any-thing:-

output=${SSH} ${DEST_USER}@${DESTHOST} "Command"
echo $output

Based on a bit research if I try it as

output=$(${SSH} ${DEST_USER}@${DESTHOST} "Command"
echo $output

I got my output stored (need to understand why?).

Secondly the output I got in a single line as:

abc_1.2.war ijk_2.2.war hij_3.2.war xyx_5.1.war

how can I format this output some thing like:

Name version
abc  1.2
ijk  2.2
hij  3.2
xyz  5.1  

Answer 1

Bash handles lines like this:

a=b c=d command

by temporarily setting environment variables "a" and "c" only for the duration of the command . They are not normal shell variables, and they won't exist after the command completes.

When you write

output=${SSH} ${DEST_USER}@${DESTHOST} "Command"

you are setting the "output" variable to the contents of "$SSH" for the duration of the "$DEST_USER@$DESTHOST" command (I'd expect you would receive a "command not found" error).

The way to capture the output of a command, as you have discovered, is with the $() syntax

output=$($SSH $DEST_USER@$DESTHOST "Command")

(Note you don't always have to put braces around your variable names, that's only strictly necessary when you need to separate the variable name from surrounding text)

---

For your text formatting question:

output="abc_1.2.war ijk_2.2.war hij_3.2.war xyx_5.1.war"
{
    echo Name version
    for word in $output; do                    # no quotes around $output here!
        IFS=_ read name version <<< "$word"
        echo "$name" "${version%.*}"
    done
} | column -t

Name  version
abc   1.2
ijk   2.2
hij   3.2
xyx   5.1

Here I use braces to group the header and the lines from the for-loop together to send them to column. I don't assume you know all the file extensions, but I do assume each file has an extension. The "${version%.*}" part removes the last dot and any following characters from the end of the value of the "version" variable.

Answer 2

尝试echo "$output" （即引号）。

Answer 3

I can't help with the 'why' right now. However you can produce the desired output from the variable(containing single line) as follows :

echo "Name   version"
echo $output | grep -Eo "[a-zA-Z]+_[0-9]+.[0-9]+"| tr '_' ' '