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POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
 

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  1. POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
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    <p>I've found that the results of my bash script will change depending upon if I execute it with debugging or not (i.e. invoking <code>set -x</code>). I don't mean that I get more output, but that the result of the program itself differs.</p> <p>I'm assuming this isn't the desired behavior, and I'm hoping that you can teach me how to correc this.</p> <p>The bash script below is a contrived example, I tried reducing the logic from the script I'm investigating so that the problem can be easily reproducible and obvious.</p> <pre><code>#!/bin/bash # Base function executes command (print working directory) stores the value in # the destination and returns the status. function get_cur_dir { local dest=$1 local result result=$((pwd) 2&gt;&amp;1) status=$? eval $dest="\"$result\"" return $status } # 2nd level function uses the base function to execute the command and store # the result in the desired location. However if the base function fails it # terminates the script. Yes, I know 'pwd' won't fail -- this is a contrived # example to illustrate the types of problems I am seeing. function get_cur_dir_nofail { local dest=$1 local gcdnf_result local status get_cur_dir gcdnf_result status=$? if [ $status -ne 0 ]; then echo "ERROR: Command failure" exit 1 fi eval dest="\"$gcdnf_result\"" } # Cause blarg to be loaded with the current directory, use the results to # create a flag_file name, and do logic with the flag_file name. function main { get_cur_dir blarg echo "Current diregtory is:$blarg" local flag_file=/tmp/$blarg.flag echo -e "&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; $flag_file" if [ "/tmp//root.flag" = "$flag_file" ]; then echo "Match" else echo "No Match" fi } main </code></pre> <p>.</p> <p>.</p> <p>When I execute without the <code>set -x</code> it works as I expect as illustrated below:</p> <pre><code>Current diregtory is:/root &gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; /tmp//root.flag Match </code></pre> <p>.</p> <p>.</p> <p>However, when I add the debugging output with -x it doesn't work, as illustrated below: root@psbu-jrr-lnx:# bash -x /tmp/example.sh </p> <pre><code>+ main + get_cur_dir blarg + local dest=blarg + local result + result='++ pwd /root' + status=0 + eval 'blarg="++ pwd /root"' ++ blarg='++ pwd /root' + return 0 + echo 'Current diregtory is:++ pwd /root' Current diregtory is:++ pwd /root + local 'flag_file=/tmp/++ pwd /root.flag' + echo -e '&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; /tmp/++ pwd /root.flag' &gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; /tmp/++ pwd /root.flag + '[' /tmp//root.flag = '/tmp/++ pwd /root.flag' ']' + echo 'No Match' No Match root@psbu-jrr-lnx:# </code></pre>
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    1. USJohn Rocha
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      1. POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
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      1. POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
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      1. POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
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      1. VTUpMod
    1. COTry `result=$((pwd) 2>&1)` => `result=$(pwd 2>&1)`
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      1. POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
      1. USJoachim Isaksson
    2. COThat did it Joachim. Do you want to change your comment to an answer so I can credit you? I had used the original syntax after reading http://stackoverflow.com/questions/3130375/bash-script-store-stderr-in-variable, but upon re-reading the post more carefully I see that they had double re-direction.
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      1. POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
      1. USJohn Rocha
    3. COThe blatant overuse of `eval` complicates your script. As far as I can tell, `eval dest="\"$gcdnf_result\""` should just be `dest=$gcdnf_result` and I have a hunch the rest of the logic could also be simplified quite a bit for improved stability and maintainability.
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      1. POWhy do I get different bash script results when invoked with 'set -x', and how do I fix it?
      1. UStripleee
 

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