On Wed, Mar 30, 2011 at 02:43:58PM +0430, ali hagigat wrote: > ---------------------------------- > var1="word1 word2" > echo $var1 > if (test -z "\"$var1\"") then > echo "first" > else > echo second > fi
Problems in this script: * Unquoted $var1 on line 2. This means that instead of passing the actual content of the variable to echo, bash is going to split it into words, perform globbing (filename expansion) on each of those words, and then pass the resulting lists of words to echo. * Unnecessary subshell invocation (parentheses) on line 3. There's no reason to create a new process there -- all it does is slow down the script. * You are testing the length of a string that will NEVER be zero-length. The string you are testing has two literal quotation marks in it, so it will ALWAYS be at least 2 characters long. The "test -z" will therefore never be true. > ---------------------------------- > var1="word1 word2" > echo $var1 > if (test -z ""$var1"") then > echo "first" > else > echo second > fi Problems in this script: * Unquoted $var1 on line 2, same as before. * Unquoted $var1 on line 3. This is even worse than the case on line 2, because when you pass multiple arguments to the test command following a -z switch, you will generate an error condition. * Unnecessary subshell, just as before. * Unnecessary use of double double quotes on line 3. All they are doing is increasing the length of the code. They have no effect. $var1 and ""$var1"" and """"""""$var1"""""""" are all the same thing. Adding zero-length strings to a string does not change the string, no matter how many of them you add. Here is what you SHOULD have done: var1="what ever" echo "$var1" if test -z "$var1"; then echo empty else echo not empty fi
