Bash integer comparison

Question

I want to write a bash script that checks if there is at least one parameter and if there is one  if that parameter is either a 0 or a 1  this is the script     bin bash if         lt  1    amp  amp        0     1           0  -ne 0q       then echo this script requires a 1 or 0 as first parameter  fi xinput set-prop 12  Device Enabled   0   This gives the following errors     setTouchpadEnabled  line 2        setTouchpadEnabled    1  syntax error  operand expected  error token is    setTouchpadEnabled    1     setTouchpadEnabled  line 2        setTouchpadEnabled -ne 0q  syntax error  operand expected  error token is    setTouchpadEnabled -ne 0q     What am I doing wrong

User · Answer

The zeroth parameter of a shell command is the command itself (or sometimes the shell itself). You should be using $1.

(("$#" < 1)) && ( (("$1" != 1)) ||  (("$1" -ne 0q)) )

Your boolean logic is also a bit confused:

(( "$#" < 1 && # If the number of arguments is less than one…
  "$1" != 1 || "$1" -ne 0)) # …how can the first argument possibly be 1 or 0?

This is probably what you want:

(( "$#" )) && (( $1 == 1 || $1 == 0 )) # If true, there is at least one argument and its value is 0 or 1

User · Answer

This script works     bin bash if            lt  1             1     1    amp  amp       1     0          then     echo this script requires a 1 or 0 as first parameter  else     echo  first parameter is  1      xinput set-prop 12  Device Enabled   0 fi   But this also works  and in addition keeps the logic of the OP  since the question is about calculations  Here it is with only arithmetic expressions     bin bash if           amp  amp      1    0     1    1     then     echo  first parameter is  1      xinput set-prop 12  Device Enabled   0 else     echo this script requires a 1 or 0 as first parameter  fi   The output is the same1       tmp sh  this script requires a 1 or 0 as first parameter       tmp sh 0 first parameter is 0      tmp sh 1 first parameter is 1      tmp sh 2 this script requires a 1 or 0 as first parameter     1  the second fails if the first argument is a string

User · Answer

Easier solution     bin bash if      1 -2   gt   2     then     echo  First parameter must be 0 or 1  fi   rest of script      Output      test  First parameter must be 0 or 1     test 0     test 1     test 4 First parameter must be 0 or 1     test 2 First parameter must be 0 or 1   Explanation         - Evaluates the expression using integers    1 -2  - Uses parameter expansion to set a value of 2 if undefined   gt   2 - True if the integer is greater than or equal to two 2

User · Answer

I know this has been answered  but here s mine just because I think case is an under-appreciated tool   Maybe because people think it is slow  but it s at least as fast as an if  sometimes faster    case   1  in     0 1  xinput set-prop 12  Device Enabled   1             echo  This script requires a 1 or 0 as first parameter      esac

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