Memcached Question posted in
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Memcached – meaning of + '[' ']' in bash -ex output

What does ‘[‘ ‘]’ indicate in this output?

$ bash -ex ~/bin/client_services 
+ : starting daemons reqd. for clients
++ ps aux
++ grep -q memcached
+ '[' ']'

My source file is:

if [ `ps aux | grep -q memcached` ]; then
  echo 'Memcached exists'
fi
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2

Answers


  1. 0

    What you’re saying here is the output of the debugging -x flag for bash. First it has to run the ps aux, then it has to run the grep .... Then it has to test the results. The [...] test syntax is an expression in itself, and also has to be evaluated.

    The + '[' ']' is the representation of that test being performed, shown to you by bash -x.

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  2. 0

    It means ps aux | grep -q memcached expanded to an empty string.

    If it didn’t you’d get what it expanded to.

    E.g.,
    ps aux | grep -q memcached prints 

    ++ echo true
+ '[' true ']'
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