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POClosing connections via s_client in a shell script
 

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    <p>I am trying to make a connection to an IMAP server within a shell script. While I can connect and issue the commands, closing the connection suitably seems impossible.</p> <p>This is the test command I am using:</p> <pre><code>openssl s_client -crlf -connect server:993 &lt;&lt;EOF 01 login USERNAME PASSWORD 02 LIST "" "*" 03 logout EOF </code></pre> <p>Because the connection is closed as soon as the input runs out, this occurs before any output is received so I never receive the required data.</p> <p>If I add the option <code>-ign_eof</code> option so that it will ignore the input ending to keep the connection open the output is returned as desired. But instead after the connection has been closed...</p> <pre><code>* BYE Logging out 03 OK Logout completed. </code></pre> <p>...s_client remains alive so execution never returns to the script.</p> <p>Is there a solution which will cause s_client to terminate when the server closes the connection?</p> <p>Or is there an alternative method using standard tools? The script would be run on Mac OS X, Debian, and a Redhat derivate, and possibly an Android terminal emulator so I would like to use fairly standard tools for portability rather than specialist packages.</p> <p>Update: I have come up with an answer that I am not entirely happy with, but which does work. It uses a script to pipe commands to the openssl but which then enters an infinite loop to keep stdin open until it receives a signal to tell it to quit. Here is my test script:</p> <pre><code>#!/bin/sh if [ "$1" = "doit" ]; then trap "echo \"04 logout\"; exit" SIGUSR1 echo "00 login USERNAME PASSWORD" echo "01 SELECT PID-$$" echo "02 SELECT FOLDER" echo "03 FETCH 1:* (BODY[HEADER.FIELDS (Subject)])" while :; do :; done fi MYFLAG= $0 doit | openssl s_client -crlf -connect server:993 2&gt;/dev/null | while read LINE; do LINE=`echo "$LINE" | tr -d '\r'` [ "${LINE:0:4}" = "* OK" ] &amp;&amp; MYFLAG=Y [ "${LINE:0:33}" = "01 NO Mailbox doesn't exist: PID-" ] &amp;&amp; PID="${LINE##*PID-}" [ "$MYFLAG" ] &amp;&amp; echo "$LINE" [ "$PID" -a "$LINE" = "03 OK Fetch completed." ] &amp;&amp; kill -USR1 $PID done echo "Finished." </code></pre> <p>The script calls itself with a parameter to output the IMAP commands which is piped to openssl, whose output is piped into a <code>read</code> loop so it can be processed. The MYFLAG variable is just used to hide the information output by openssl and just echo the output from the server connection.</p> <p>I select a dummy folder name which includes the PID of the second instance of the script as a way to pass this back, obviously a temporary file would have been better but for the testing I wanted to keep everything self contained and be able to watch what was happening.</p> <p>Once the fetch information has been displayed and the server returns the OK response, it sends a SIGUSR1 signal to the second instance of the script, that then sends the logout message and quits, closing stdin which causes s_client to disconnect.</p> <p>Originally I included the <code>04 logout</code> command in the initial set of echos, but when I did this the read loop only displayed as far as the fetch output then stalled, it did not even show the OK status for the operation, though everything was received.</p> <p>Also I need to use <code>tr</code> to strip trailing carriage returns, but if I pipe the output from openssl through then nothing is received by the read loop.</p>
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