Using unset vs setting a variable to empty

Question

I m currently writing a bash testing framework  where in a test function  both standard bash tests      as well as predefined matchers can be used  Matchers are wrappers to      and besides returning a return code  set some meaningful message saying what was expected   Example   string equals         if       1    2     then             error message  Expected   1  to be   2                 return 1     fi     So  when a matcher is used  and it fails  only then an error message is set   Now  at some point later  I test whether the tests succeeded  If it succeeded  I print the expectation in green  if it failed in red   Furthermore  there may be an error message set  so I test if a message exists  print it  and then unset it  because the following test may not set an error message    if     error message     then     printf   s n    error message       unset -v error message fi   Now my question is  if it is better to unset the variable  or to just set it to     like  error message      Which one is better  Does it actually make a difference  Or maybe should I have an additional flag indicating that the message was set

User · Answer

As has been said  using unset is different with arrays as well    foo  4 5 6     foo 2      echo    foo     3    unset foo 2     echo    foo     2

User · Answer

So  by unset ting the array index 2  you essentially remove that element in the array and decrement the array size       I made my own test    foo  5 6 8  echo    foo     unset foo echo    foo       Which results in    3 0   So just to clarify that unset ting the entire array will in fact remove it entirely

User · Answer

Mostly you don t see a difference  unless you are using set -u    home user1 gt  var     home user1 gt  echo  var   home user1 gt  set -u  home user1 gt  echo  var   home user1 gt  unset var  home user1 gt  echo  var -bash  var  unbound variable   So really  it depends on how you are going to test the variable   I will add that my preferred way of testing if it is set is      -n  var       True if the length of  var is non-zero   or     -z  var       True if zero length

User · Answer

Based on the comments above  here is a simple test   isunset            1       x      amp  amp         1-x       x      amp  amp  echo 1    isset         -z    isunset   1       amp  amp  echo 1      Example     unset foo       isunset foo      amp  amp  echo  It s unset     echo  It s set  It s unset   foo             isunset foo      amp  amp  echo  It s unset     echo  It s set  It s set   foo bar         isunset foo      amp  amp  echo  It s unset     echo  It s set  It s set

[bash] Using unset vs. setting a variable to empty

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