Null empty string comparison in Bash

Question

I don t set any values for  pass tc11  so it is returning null while echoing  How to compare it in if clause   Here is my code  I don t want  Hi  to be printed     -bash-3 00  echo  pass tc11  -bash-3 00  if    pass tc11           then  gt  echo  hi   gt  fi hi -bash-3 00

User · Answer

fedorqui has a working solution but there is another way to do the same thing.

Chock if a variable is set

#!/bin/bash
amIEmpty='Hello'
# This will be true if the variable has a value
if [ $amIEmpty ]; then
    echo 'No, I am not!';
fi

Or to verify that a variable is empty

#!/bin/bash      
amIEmpty=''
# This will be true if the variable is empty
if [ ! $amIEmpty ]; then
    echo 'Yes I am!';
fi

tldp.org has good documentation about if in bash:
http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html

User · Answer

First of all  note you are not using the variable correctly   if    pass tc11           then               missing     Anyway  to check if a variable is empty or not you can use -z --  the string is empty   if     -z   pass tc11     then    echo  hi  I am not empty  fi   or -n --  the length is non-zero   if   -n   pass tc11     then    echo  hi  I am not empty  fi   From man test      -z STRING      the length of STRING is zero      -n STRING      the length of STRING is nonzero   Samples         -z   var     amp  amp  echo  yes       var          -z   var     amp  amp  echo  yes       var  a        -z   var     amp  amp  echo  yes  yes    var  a      -n   var     amp  amp  echo  yes  yes

[bash] Null & empty string comparison in Bash

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