Error [: -lt: unary operator expected in shell script Linux












2















I get error [: -lt: unary operator expected after run below script, anyone can share ideas?



temp=0
while [ $temp -lt 25 ]
do
sleep 1
echo "running.."

if [ $temp -eq 5 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
break
elif [ $temp -eq 20 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
else
temp=`expr $temp +1`
fi
done









share|improve this question









New contributor




Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 1





    Do you also get errors from expr?

    – Michael Homer
    3 hours ago











  • no error shown on expr

    – Shi Jie Tio
    3 hours ago











  • Use More Quotes™

    – l0b0
    2 hours ago
















2















I get error [: -lt: unary operator expected after run below script, anyone can share ideas?



temp=0
while [ $temp -lt 25 ]
do
sleep 1
echo "running.."

if [ $temp -eq 5 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
break
elif [ $temp -eq 20 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
else
temp=`expr $temp +1`
fi
done









share|improve this question









New contributor




Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
















  • 1





    Do you also get errors from expr?

    – Michael Homer
    3 hours ago











  • no error shown on expr

    – Shi Jie Tio
    3 hours ago











  • Use More Quotes™

    – l0b0
    2 hours ago














2












2








2








I get error [: -lt: unary operator expected after run below script, anyone can share ideas?



temp=0
while [ $temp -lt 25 ]
do
sleep 1
echo "running.."

if [ $temp -eq 5 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
break
elif [ $temp -eq 20 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
else
temp=`expr $temp +1`
fi
done









share|improve this question









New contributor




Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












I get error [: -lt: unary operator expected after run below script, anyone can share ideas?



temp=0
while [ $temp -lt 25 ]
do
sleep 1
echo "running.."

if [ $temp -eq 5 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
break
elif [ $temp -eq 20 ]
then
top -bc -d 5 -n 1|sed -n '7,8p'|awk '{print $1,$9}'>>out.txt
temp=`expr $temp +1`
else
temp=`expr $temp +1`
fi
done






linux shell-script test






share|improve this question









New contributor




Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question









New contributor




Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




share|improve this question








edited 3 hours ago









Jeff Schaller

39.3k1054125




39.3k1054125






New contributor




Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 3 hours ago









Shi Jie TioShi Jie Tio

1163




1163




New contributor




Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Shi Jie Tio is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.








  • 1





    Do you also get errors from expr?

    – Michael Homer
    3 hours ago











  • no error shown on expr

    – Shi Jie Tio
    3 hours ago











  • Use More Quotes™

    – l0b0
    2 hours ago














  • 1





    Do you also get errors from expr?

    – Michael Homer
    3 hours ago











  • no error shown on expr

    – Shi Jie Tio
    3 hours ago











  • Use More Quotes™

    – l0b0
    2 hours ago








1




1





Do you also get errors from expr?

– Michael Homer
3 hours ago





Do you also get errors from expr?

– Michael Homer
3 hours ago













no error shown on expr

– Shi Jie Tio
3 hours ago





no error shown on expr

– Shi Jie Tio
3 hours ago













Use More Quotes™

– l0b0
2 hours ago





Use More Quotes™

– l0b0
2 hours ago










1 Answer
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oldest

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4














Try changing all the +1s after the exprs to + 1.



Without the space expr will return an error and $temp will be empty. If $temp is empty, then the -lt will be comparing a blank space to a number, which is why the error appears. Here's a one liner that reproduces the problem:



t=0;t=`expr $t +1`;[ $t -lt 25 ]


Output (to STDERR):



expr: syntax error
bash: [: -lt: unary operator expected


Better yet, change all code that uses the external util expr to use the shell's own internal arithmetic expansion. So code like this:



temp=`expr $temp +1`


...should be changed to:



temp=$(($temp + 1))





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    1 Answer
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    active

    oldest

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    1 Answer
    1






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    4














    Try changing all the +1s after the exprs to + 1.



    Without the space expr will return an error and $temp will be empty. If $temp is empty, then the -lt will be comparing a blank space to a number, which is why the error appears. Here's a one liner that reproduces the problem:



    t=0;t=`expr $t +1`;[ $t -lt 25 ]


    Output (to STDERR):



    expr: syntax error
    bash: [: -lt: unary operator expected


    Better yet, change all code that uses the external util expr to use the shell's own internal arithmetic expansion. So code like this:



    temp=`expr $temp +1`


    ...should be changed to:



    temp=$(($temp + 1))





    share|improve this answer






























      4














      Try changing all the +1s after the exprs to + 1.



      Without the space expr will return an error and $temp will be empty. If $temp is empty, then the -lt will be comparing a blank space to a number, which is why the error appears. Here's a one liner that reproduces the problem:



      t=0;t=`expr $t +1`;[ $t -lt 25 ]


      Output (to STDERR):



      expr: syntax error
      bash: [: -lt: unary operator expected


      Better yet, change all code that uses the external util expr to use the shell's own internal arithmetic expansion. So code like this:



      temp=`expr $temp +1`


      ...should be changed to:



      temp=$(($temp + 1))





      share|improve this answer




























        4












        4








        4







        Try changing all the +1s after the exprs to + 1.



        Without the space expr will return an error and $temp will be empty. If $temp is empty, then the -lt will be comparing a blank space to a number, which is why the error appears. Here's a one liner that reproduces the problem:



        t=0;t=`expr $t +1`;[ $t -lt 25 ]


        Output (to STDERR):



        expr: syntax error
        bash: [: -lt: unary operator expected


        Better yet, change all code that uses the external util expr to use the shell's own internal arithmetic expansion. So code like this:



        temp=`expr $temp +1`


        ...should be changed to:



        temp=$(($temp + 1))





        share|improve this answer















        Try changing all the +1s after the exprs to + 1.



        Without the space expr will return an error and $temp will be empty. If $temp is empty, then the -lt will be comparing a blank space to a number, which is why the error appears. Here's a one liner that reproduces the problem:



        t=0;t=`expr $t +1`;[ $t -lt 25 ]


        Output (to STDERR):



        expr: syntax error
        bash: [: -lt: unary operator expected


        Better yet, change all code that uses the external util expr to use the shell's own internal arithmetic expansion. So code like this:



        temp=`expr $temp +1`


        ...should be changed to:



        temp=$(($temp + 1))






        share|improve this answer














        share|improve this answer



        share|improve this answer








        edited 2 hours ago

























        answered 3 hours ago









        agcagc

        4,50311036




        4,50311036






















            Shi Jie Tio is a new contributor. Be nice, and check out our Code of Conduct.










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