Check if string is neither empty nor space in shell script

Question

I am trying to run the following shell script which is supposed to check if a string is neither space nor empty  However  I am getting the same output for all the 3 mentioned strings  I have tried using the      syntax as well but to no avail   Here is my code   str  Hello World  str2     str3     if     -z   str  -a   str          then         echo  Str is not null or space  fi  if     -z   str2  -a   str2          then         echo  Str2 is not null or space  fi  if     -z   str3  -a   str3          then         echo  Str3 is not null or space  fi   I am getting the following output       checkCond sh  Str is not null or space Str2 is not null or space

User · Answer

To check if a string is empty or contains only whitespace you could use:

shopt -s extglob  # more powerful pattern matching

if [ -n "${str##+([[:space:]])}" ]; then
    echo '$str is not null or space'
fi

See Shell Parameter Expansion and Pattern Matching in the Bash Manual.

User · Answer

For checking the empty string in shell  if     str          then    echo NULL fi   OR  if       str    then    echo NULL fi

User · Answer

In case you need to check against any amount of whitespace  not just single space  you can do this   To strip string of extra white space  also condences whitespace in the middle to one space    trimmed  echo --  original    The -- ensures that if  original contains switches understood by echo  they ll still be considered as normal arguments to be echoed  Also it s important to not put    around  original  or the spaces will not get removed   After that you can just check if  trimmed is empty     -z   trimmed     amp  amp  echo  empty

User · Answer

You need a space on either side of the     Change your code to   str  Hello World  str2     str3     if     -z   str  -a   str            then         echo  Str is not null or space  fi  if     -z   str2  -a   str2            then         echo  Str2 is not null or space  fi  if     -z   str3  -a   str3            then         echo  Str3 is not null or space  fi

User · Answer

echo  variable to test   sed s  n     sed s                amp  amp  echo  String is empty    Stripping all newlines and spaces from the string will cause a blank one to be reduced to nothing which can be tested and acted upon

User · Answer

Another quick test for a string to have something in it but space   if    -n    str           then     echo  It is not empty   fi    -n  means non-zero length string   Then the first two slashes mean match all of the following  in our case space s   Then the third slash is followed with the replacement  empty  string and closed with      Note the difference from the usual regular expression syntax   You can read more about string manipulation in bash shell scripting here

[bash] Check if string is neither empty nor space in shell script

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