How to compare numbers in bash

Question

I m unable to get numeric comparisons working  echo  quot enter two numbers quot   read a b   echo  quot a  a quot   echo  quot b  b quot    if    a   gt   b    then      echo  quot a is greater than b quot   else     echo  quot b is greater than a quot   fi   The problem is that it compares the number from the first digit on  i e  9 is bigger than 10  but 1 is greater than 09  How can I convert the numbers into a type to do a true comparison

User · Answer

Like this     bin bash  a 2462620 b 2462620  if    quot  a quot  -eq  quot  b quot     then   echo  quot They re equal quot   fi  Integers can be compared with these operators  -eq   equal -ne   not equal -lt   less than -le   less than or equal -gt   greater than -ge   greater than or equal  See this cheatsheet  https   devhints io bash conditionals

User · Answer

I solved this by using a small function to convert version strings to plain integer values that can be compared   function versionToInt       local IFS     parts   1    let val 1000000 parts 0  1000 parts 1  parts 2    echo  val     This makes two important assumptions    Input is a  normal SemVer string  Each part is between 0-999   For example  versionToInt 12 34 56    -- gt  12034056 versionToInt 1 2 3       -- gt   1002003   Example testing whether npm command meets minimum requirement      NPM ACTUAL   versionToInt   npm --version      Capture npm version NPM REQUIRED   versionToInt 4 3 0              Desired version if    NPM ACTUAL   lt   NPM REQUIRED    then   echo  Please update to npm latest    exit 1 fi

User · Answer

In Bash I prefer doing this as it addresses itself more as a conditional operation unlike using       which is more of arithmetic      N -gt M      Unless I do complex stuffs like      N   1   gt  M      But everyone just has their own preferences  Sad thing is that some people impose their unofficial standards   Update   You actually can also do this       N   1  -gt M      Which allows you to add something else which you could do with       besides arithmetic stuff

User · Answer

This code can also compare floats  It is using awk  it is not pure bash   however this shouldn t be a problem  as awk is a standard POSIX command that is most likely shipped by default with your operating system     awk  BEGIN  return code  -1 2345    -1 2345    0   1  exit  END  exit return code     echo    0   awk  BEGIN  return code  -1 2345  gt   -1 2345    0   1  exit  END  exit return code     echo    0   awk  BEGIN  return code  -1 2345  lt  -1 2345    0   1  exit  END  exit return code     echo    1   awk  BEGIN  return code  -1 2345  lt  2    0   1  exit  END  exit return code     echo    0   awk  BEGIN  return code  -1 2345  gt  2    0   1  exit  END  exit return code     echo      To make it shorter for use  use this function   compare nums          Function to compare two numbers  float or integers  by using awk       The function will not print anything  but it will return 0  if the comparison is true  or 1       if the comparison is false  exit codes  so it can be used directly in shell one liners                          Usage            Note that you have to enclose the comparison operator in quotes                        compare nums 1   gt   2   returns false      compare nums 1 23   lt    2   returns true      compare nums -1 238   lt    -2   returns false                                                     num1  1    op  2    num2  3    E BADARGS 65       Make sure that the provided numbers are actually numbers     if       num1     -  0-9       0-9          then  gt  amp 2 echo   num1 is not a number   return  E BADARGS  fi    if       num2     -  0-9       0-9          then  gt  amp 2 echo   num2 is not a number   return  E BADARGS  fi       If you want to print the exit code as well  instead of only returning it   uncomment      the awk line below and comment the uncommented one which is two lines below      awk  BEGIN  print return code    num1    op    num2     0   1  exit  END  exit return code      awk  BEGIN  return code    num1    op    num2     0   1  exit  END  exit return code      return code       return  return code      compare nums -1 2345   gt    -1 2345  amp  amp  echo true    echo false true   compare nums -1 2345   gt    23  amp  amp  echo true    echo false false

User · Answer

The bracket stuff  e g       a -gt  b    or     a  gt   b      isn t enough if you want to use float numbers as well  it would report a syntax error  If you want to compare float numbers or float number to integer  you can use      bc  lt  lt  lt               For example   a 2 00 b 1  if      bc  lt  lt  lt   a  gt   b       then      echo  a is greater than b  else     echo  a is not greater than b  fi   You can include more than one comparison in the if statement  For example   a 2  b 1 c 1 0000  if      bc  lt  lt  lt   b     c  amp  amp   b  lt   a       then      echo  b is equal to c but less than a  else     echo  b is either not equal to c and or not less than a  fi   That s helpful if you want to check if a numeric variable  integer or not  is within a numeric range

User · Answer

In bash  you should do your check in arithmetic context   if    a  gt  b     then         fi   For POSIX shells that don t support       you can use -lt and -gt   if     a  -gt   b     then         fi   You can get a full list of comparison operators with help test or man test

User · Answer

If you have floats you can write a function and then use that e g      bin bash  function float gt         perl -e   if  1 gt  2  print 1  else  print 0       x 3 14 y 5 20 if     float gt  x  y     1     then     echo  do stuff with x  else     echo  do stuff with y  fi

User · Answer

There is also one nice thing some people might not know about   echo     a  lt  b   a   b      This code will print the smallest number out of a and b

[bash] How to compare numbers in bash?

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