conditional binary operator expected error when the file is empty in shell script

Question

i have a file called MYNAME in path /root/user/ which has some value say SSS_14_10_1992

when the values exists in file the below code works fine but when the file is empty , then the below mentioned error is thrown

i am reading this value from file and matching it wildcard and doing something , when the file has some value the below code works fine , when the file is empty then i am getting conditional error

Below is my code

var=$(cat /root/user/MYNAME)

echo $var

su - uname<<!
pwd

if  [ -z "$var" ]; then
   echo "NAME SHOULD BE PROVIDED IN MYNAME FILE"
else
   if [[ $var == SSS_14_10* ]]
     then
     echo "value is matched"
   else
     echo "value has not matched"
   fi
fi
!

when the file is empty i am getting the below error:

: conditional binary operator expected
: syntax error near `SSS_14_10*'
: `   if [[  == SSS_14_10* ]]'

Try putting var=$(cat /root/user/MYNAME) after su. Not sure if the variables defined for one user would withstand a su command. I guess it doesn't. — sjsam
– sjsam, Commented Jan 25, 2018 at 10:35
Also you could replace the assignment using var=$(</root/user/MYNAME) — sjsam
– sjsam, Commented Jan 25, 2018 at 10:38
are you trying to "match" when the right-hand-side expression is SSS_14_10* (the *)? Use =~ instead. (or is it ~=?) . Good luck. — shellter
– shellter, Commented Jan 25, 2018 at 13:53
@sjsam thanks for the reply if i put it inside su it's throwing error like to put that outside subshell — sachin sarangamath
– sachin sarangamath, Commented Jan 26, 2018 at 3:41
@shelter thanks for the reply , as u side i am trying to do match with wildcard on right hand side — sachin sarangamath
– sachin sarangamath, Commented Jan 26, 2018 at 3:42

Alex Stiff · Accepted Answer · 2018-01-25 12:15:49Z

3

Try to compare "$var" (with quotes) instead of $var (without quotes). This way if the variable is empty you're just comparing "".

answered Jan 25, 2018 at 12:15

Alex Stiff

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Comments

chepner · Accepted Answer · 2018-01-27 17:35:44Z

2

Don't generate code dynamically like this. Pass the value of $var as a parameter to the script run by su.

var=$(cat /root/user/MYNAME)

echo "$var"

su - uname<<'!' "$var"
pwd

if  [ -z "$1" ]; then
   echo "NAME SHOULD BE PROVIDED IN MYNAME FILE"
elif [[ $1 == SSS_14_10* ]]; then
   echo "value is matched"
else
   echo "value has not matched"
fi
!

Note the single quotes around the here-doc delimiter; this ensures the here document is seen as-is by su, so that nothing further needs escaping.

edited Jan 27, 2018 at 17:35

answered Jan 27, 2018 at 17:15

chepner

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