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Markus
Asked: 2014-11-02 06:40:36 +0800 CST

Strange echo behavior

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To boil it down: The following command in bash

echo $(ssh -t pi@doctor "sudo stat -c \"%U\" /var/www/candy/example/index.html")101

Gives the this result

Connection to doctor closed.
101-data

While

echo $(ssh -t pi@doctor "sudo stat -c \"%U\" /var/www/candy/example/index.html")

gives

Connection to doctor closed.
www-data

Why is this?

Background: I'm using this script (called ced.sh):

for ARG; do
        name=${ARG##*/}
        echo name=$name
        path=${ARG%/*} 
        echo path=$path
        owner=$(echo $(ssh -t $remote_user@$server "sudo stat -c \"%U\" $ARG"))
        echo owner=$owner
        group=$(echo $(ssh -t $remote_user@$server "sudo stat -c \"%G\" $ARG"))
        echo group=$group
        perms=$(echo $(ssh -t $remote_user@$server "sudo stat -c \"%a\" $ARG"))
        echo perms=$perms
        read -p "Gibt es einen Dienst/Server, der auf diese Datei zurückgreift (notfalls leer lassen)? " service
        echo service=$service
        echo "name="\"$name\" "path="\"$path/\" "owner="\"$owner\" "group="\"$group\" "perms="$perms "service="$service
done

Its purpose is to read some information (e.g. owner, group, permissions) from files on a server, which I'd like to edit locally. The last line should produce an output that can be stored in a file.

It would have been rewritten to:

echo "name="\"$name\" "path="\"$path/\" "owner="\"$owner\" "group="\"$group\" "perms="$perms "service="$service >> "$HOME/...bla bla..."

The output looks like this:

Software/EigeneProgramme/ced.sh -p /var/www/candy/example/index.html
name=index.html
path=/var/www/candy/example
Connection to doctor closed.
owner=www-data
Connection to doctor closed.
group=www-data
Connection to doctor closed.
perms=644
Gibt es einen Dienst/Server, der auf diese Datei zurückgreift (notfalls leer lassen)? apache
service=apache
 service=apacheta path="/var/www/candy/example/" owner="www-data

I don't understand why echo produces the last line. It seems that it is writing to line in on. Did I forget to escape something?

bash

1 Answers

  1. There is an easy explanation for this. The values retrieved from the remote server all come with a trailing carriage return (\r).

    You were expecting this:

    www-data101

name="index.html" path="/var/www/candy/example/" owner="www-data" group="www-data" perms=644 service=apache

    But www-data and 644 are followed by a carriage return. If CR would be rendered as a newline by your terminal emulator, then the output would look like this:

    www-data
101

name="index.html" path="/var/www/candy/example/" owner="www-data
" group="www-data
" perms=644
 service=apache

    Without the linefeeds, lines overlap; the dots represent the characters that are overwritten.

    ...-data
101

................. path="/var/www/candy/example/" owner="www-data
...............ta
...........
 service=apache

    As you already pointed out, on most terminals this looks like:

    101-data

 service=apacheta path="/var/www/candy/example/" owner="www-data

    You can verify this by piping the remote output to cat -v; the carriage return will show up as ^M.

    ssh -t pi@doctor "sudo stat -c \"%U\" /var/www/candy/example/index.html" | cat -v

    One possible solution is to strip off the carriage return by piping the remote output through tr -d '\r':

    ssh -t pi@doctor "sudo stat -c \"%U\" /var/www/candy/example/index.html" | tr -d '\r'
    • 3