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Accepted
Sourav
Asked: 2011-08-18 18:58:23 +0800 CST

Arithmetic binary operators -gt, -lt give error but work in a shell script

  • 772

I wrote this simple script it works too but shows an error

clear
echo Enter 1st number
read n1
echo Enter 2nd number
read n2
echo MUlti is `expr $n1 \* $n2`;
if [$n1 -lt $n2]
then
 echo $n1 'is bigger than' $n2
else
 echo $n2 'is bigger than' $n1
fi

output

Enter 1st number
5
Enter 2nd number
10
MUlti is 50
./script.sh: line 7: [5: command not found
10 is bigger than 5
command-line

2 Answers

  1. Best Answer

    The [ is a command builtin, also known as test, and as all commands requires at least a space to separate it from other words in the command. [ is also available as a regular command in /usr/bin/[ or /usr/bin/test.

    The presence of a final ] is instead a requirement of the command, when invoked as [, and the spaces around it are required as for every parameter of a command.

    That said, in bash you should use the command [[, that has some avantages over [, like for example supporting && and || for logical operations, beside -a and -o.

    Moreover, to do integer arithmetic operations and comparison between integers it is better to use arithmetic expansions $((math operations)), and the corresponding command ((math ops)).

    With these observations, your script could be:

    #!/bin/bash

clear
echo "Enter 1st number"
read n1
echo "Enter 2nd number"
read n2
echo "Multi is $((n1 * n2))"
if ((n1 > n2)); then
  echo "$n1 is bigger than $n2"
else
  echo "$n2 is bigger than $n1"
fi

    Remember to make it executable (chmod +x my-script), then execute it with ./my-script.

    • 9

  2. For bash conditional if statements, you need to have a whitespace right before and right after your condition. Yours should look like:

    if [ $n1 -lt $n2 ]

    instead of

    if [$n1 -lt $n2]

    Goofy, but that's the bash shell.

    • 5