Bash script in Prey project formatted incorrectly? Nested backtick issue?

Question

I'm a terrible beginner at bash scripting, and am hoping someone can help me out with this issue.

Having a problem with the Prey project standalone scripts. There's a line that's supposed to send an email, and apparently its not formatted correctly.

response=`mailsender -f "$mail_from" -t "$mail_to" -u "$complete_subject" \
          -s $smtp_server -a $file_list -o message-file="$trace_file.msg" \
          tls=auto username=$smtp_username \
          password=\`decrypt \"$smtp_password\"\``

Where mailsender is an alias to Brandon Zehm's PERL sendEmail script, $smtp_password is a pointless base64 encoding of the password, and decrypt is:

decrypt() {
    echo "$1" | openssl enc -base64 -d
}

So can anyone tell me what's wrong with the script? For reference, if I just replace the entire decrypt part with the plaintext password, it works fine. i.e.:

response=`mailsender -f "$mail_from" -t "$mail_to" -u "$complete_subject" \
          -s $smtp_server -a $file_list -o message-file="$trace_file.msg" \
          tls=auto username=$smtp_username password=actual_password`

Wait, you're trying to call a *function* with *command substitution*? — Ignacio Vazquez-Abrams, Dec 22 '10 at 02:30
@Ignacio: why wouldn't it work? The forked child shell has the same function available. Empirically, it works - but it would be hell getting the example script I used into a comment because of the backticks! — Jonathan Leffler, Dec 22 '10 at 05:16

score 2 · Answer 1 · answered Dec 22 '10 at 04:15

2

The simplest thing to do is avoid backticks, and use $() instead -- they nest cleanly, with no special escaping needed:

response=$(Documents/Projects/Shell\ Scripting/printargs -f "$mail_from" \
    -t "$mail_to" -u "$complete_subject" -s $smtp_server -a $file_list \
    -o message-file="$trace_file.msg"  tls=auto username=$smtp_username \
    password="$(decrypt "$smtp_password")")

answered Dec 22 '10 at 04:15

Gordon Davisson

118,432
16
123
151

+1: This alternative notation is by far the best way of dealing with the problems. – Jonathan Leffler Dec 22 '10 at 05:18

score 0 · Answer 2 · answered Dec 22 '10 at 05:30

I think this script is isomorphic with yours:

decrypt()
{
    echo "$1" | tr 'a-z' 'A-Z'
}
xxx=`echo xxx=yyy pass=\`decrypt \"xyz abc\"\``
echo "$xxx"

When run with 'sh -x xxx' (where 'sh' is 'bash' in disguise):

$ sh -x xxx
+++ decrypt '"xyz' 'abc"'
+++ echo '"xyz'
+++ tr a-z A-Z
++ echo xxx=yyy 'pass="XYZ'
+ xxx='xxx=yyy pass="XYZ'
+ echo 'xxx=yyy pass="XYZ'
xxx=yyy pass="XYZ
$

You can see where there are problems - if you know how to look. The decrypt command line has two arguments where the intention was to have just one, and the arguments include a double quote before the first and another at the end of the second.

So, in your script, the argument passed to decrypt includes a pair of double quotes, which probably isn't what you wanted.

If we rewrite the script using the '$(...)' notation, which nests much more neatly, then we get:

decrypt()
{
    echo "$1" | tr 'a-z' 'A-Z'
}

yyy=$(echo zzz=yyy pass=$(decrypt "xyz abc"))
echo "$yyy"

The trace from this looks like:

$ sh -x xxx
+++ decrypt 'xyz abc'
+++ echo 'xyz abc'
+++ tr a-z A-Z
++ echo zzz=yyy pass=XYZ ABC
+ yyy='zzz=yyy pass=XYZ ABC'
+ echo 'zzz=yyy pass=XYZ ABC'
zzz=yyy pass=XYZ ABC
$

tomaspollak · Answer 3 · 2010-12-23T04:07:54.320

I'm one of the guys from Prey. This bug was confimed yesterday and a fix has already been commited.

I do agree that $() is much easier to read than backticking -- and specially back-backticking --, and actually that's one of the things we're working on (big code refactoring).

Lately I've been working on a Bash framework called Skull which provides a much nicer interface for writing shell scripts. Hopefully Prey 0.6 will be based completely on it, and excessive backticking will be replaced with $() to make it easier for everyone to read.

Bash script in Prey project formatted incorrectly? Nested backtick issue?

3 Answers3

Linked