Bash: if condition as variable

Shell Programming and Scripting
1

How can I use a variable that has the conditions for the if statement stored in it?

my test script

condition="[ a = b ] || [ a = a ] || [ c = a ]"

if "$condition"
   then echo "true"
   else echo "false"
fi

output

$ ./test2.sh
./test2.sh: line 3: [ a = b ] || [ a = a ] || [ c = a ]: command not found
false
2

Use the eval command and build the condition string as:

condition="[ $a = $b -o  $a = $a -o  $c = $a ]"

if eval "$condition"
then 
  echo "true"
else 
  echo "false"
fi
3

Thank You, Franklin52.

Adding eval after the if did the trick. I added it on line 28 of the test script below.

my final test script

#!/bin/bash
#test.sh

fileType=( avi flv iso mkv mp4 mpeg mpg wmv )

if [ -n "$1" ]
then
   inputFileName="$1"
   echo "\$1 = $1"
   echo "inputFileName = $inputFileName"
else
   for inputFileName in *
   do
      if [ -f "$inputFileName" ]
         then
            echo -e "\ninputFileName = $inputFileName"
            fileNameExt=`echo $inputFileName|sed 's/.*\.//'`
            predicate="[ \"$fileType\" = \"$fileNameExt\" ]"

            if [ ${#fileType[@]} != 0 ]
            then
               i="1"
               while [ $i -lt ${#fileType[@]} ]
               do
                  predicateN=""
                  predicateN=`echo -e "$predicateN|| [ \"${fileType}\" = \"$fileNameExt\" ]"`
                  predicate="$predicate $predicateN"
                  i=$[$i+1]
               done
            fi

            if eval "$predicate"
            then
               echo "yes, $inputFileName has a usable file extension."
            fi
      fi
   done
fi

exit

sample output

$ ./test.sh 

inputFileName = bill.mkv
yes, bill.mkv has a usable file extension.

inputFileName = bob.mkv
yes, bob.mkv has a usable file extension.

inputFileName = examples.desktop