How do I test if a variable is a number in Bash

Question

I just can t figure out how do I make sure an argument passed to my script is a number or not   All I want to do is something like this   test  isnumber   1  amp  amp  VAR  1    echo  need a number    Any help

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The accepted answer didn t work for me in all cases BASH 4  so      -- is var an integer  --   trim leading trailing whitespace  then check for digits return 0 or 1   Globals  None   Arguments  string   Returns  boolean   -- is int         str    echo -e    1     sed -e  s     space        -e  s    space               case   str  in       0-9    return 1    esac     return 0     How to use it    Valid  will return 0   true    is int  100   amp  amp  echo  return 0     echo  return 1    Invalid  will return 1   false     is int  100abc   amp  amp  echo  returned 0     echo  returned 1  is int      amp  amp  echo  returned 0     echo  returned 1  is int  100 100    amp  amp  echo  returned 0     echo  returned 1  is int            amp  amp  echo  returned 0     echo  returned 1  is int  NOT SET VAR   amp  amp  echo  returned 0     echo  returned 1  is int  3 14     amp  amp  echo  returned 0     echo  returned 1    Output   returned 0 returned 1 returned 1 returned 1 returned 1 returned 1 returned 1   note  in Bash  1   false  0   true  I am simply printing it out where instead something like this would be more likely     if is int   total    then       perform some action  fi

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I tried ultrasawblade s recipe as it seemed the most practical to me  and couldn t make it work  In the end i devised another way though  based as others in parameter substitution  this time with regex replacement         var       digit            amp  amp  echo   var is not numeric     echo   var is numeric    It removes every  digit  class character in  var and checks if we are left with an empty string  meaning that the original was only numbers   What i like about this one is its small footprint and flexibility  In this form it only works for non-delimited  base 10 integers  though surely you can use pattern matching to suit it to other needs

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The accepted answer does not work here  I am on MacOS  The following code works   if     echo   number    grep -c    0-9         0    then      echo  it is a number  else     echo  not a number  fi

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Just a follow up to  mary  But because I don t have enough rep  couldn t post this as a comment to that post  Anyways  here is what I used   isnum     awk -v a   1   BEGIN  print  a    a   0         The function will return  1  if the argument is a number  otherwise will return  0   This works for integers as well as floats  Usage is something like   n -2 05e 07 res  isnum   n   if     res      1     then      echo   n is a number  else      echo   n is not a number  fi

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Nobody suggested bash s extended pattern matching      1      -    0-9       amp  amp  echo  quot  1 is an integer quot   or using new POSIX style      1      -     digit        amp  amp  echo  quot  1 is an integer quot

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Below is a Script written by me and used for a script integration with Nagios and it is working properly till now     bin bash   Script to test variable is numeric or not   Shirish Shukla   Pass arg1 as number a1  1 a   echo  a1 awk   if  1  gt  0  print  1  else print  1  -1     b   echo  scale 2  a  a   1    bc -l 2 gt  dev null  if     b  gt  1    then     echo   1 is Numeric  else     echo   1 is Non Numeric  fi   EG     sh isnumsks sh    -22 22  -22 22 is Numeric    sh isnumsks sh    22 22  22 22 is Numeric    sh isnumsks sh    shirish22 22  shirish22 22 is Non  Numeric

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variable to check  number 12345 or number -23234 or number 23 167 or number -345 234 check numeric or non-numeric  echo  number   grep -E   -  0-9      0-9      gt   dev null decide on further actions based on the exit status of the above  if      -eq 0    then echo  Numeric   else echo  Non-Numeric   fi

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printf   b   -123 nABC    tr    space          grep -q   -     digit         amp  amp  echo  Integer      echo  NOT integer     Remove the -   in grep matching pattern if you don t accept negative integer

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Can t comment yet so I ll add my own answer  which is an extension to glenn jackman s answer using bash pattern matching   My original need was to identify numbers and distinguish integers and floats  The function definitions deducted to   function isInteger              1       -    0-9         function isFloat              1       -      0-9      0-9      0-9      0-9     E  -      0-9           I used unit testing  with shUnit2  to validate my patterns worked as intended   oneTimeSetUp         int values  0 123 -0 -123      float values  0 0 0   0 -0 0 -0  - 0           123 456 123   456 -123 456 -123  - 456         123 456E08 123 E08  456E08 -123 456E08 -123 E08 - 456E08           123 456E 08 123 E 08  456E 08 -123 456E 08 -123 E 08 - 456E 08           123 456E-08 123 E-08  456E-08 -123 456E-08 -123 E-08 - 456E-08     testIsIntegerIsFloat         local value     for value in   int values      do         assertTrue    value  should be tested as integer   isInteger   value           assertFalse    value  should not be tested as float   isFloat   value       done      for value in   float values      do         assertTrue    value  should be tested as float   isFloat   value           assertFalse    value  should not be tested as integer   isInteger   value       done      Notes  The isFloat pattern can be modified to be more tolerant about decimal point         and the E symbol    Ee    My unit tests test only values that are either integer or float  but not any invalid input

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A clear answer has already been given by  charles Dufy and others  A pure bash solution would be using the following    string  -12 345  if      string      -  0-9        0-9       then     echo  string is a number else     echo  string is not a number fi   Although for real numbers it is not mandatory to have a number before the radix point   To provide a more thorough support of floating numbers and scientific notation  many programs in C Fortran or else will export float this way   a useful addition to this line would be the following    string  1 2345E-67  if      string      -  0-9        0-9   eE  -  0-9       then     echo  string is a number else     echo  string is not a number fi   Thus leading to a way to differentiate types of number  if you are looking for any specific type    string  -12 345  if      string      -  0-9       then     echo  string is an integer elif      string      -  0-9        0-9       then     echo  string is a float elif      string      -  0-9        0-9   eE -  0-9       then     echo  string is a scientific number else     echo  string is not a number fi   Note  We could list the syntactical requirements for decimal and scientific notation  one being to allow comma as radix point  as well as      We would then assert that there must be only one such radix point  There can be two   - signs in an  Ee  float  I have learned a few more rules from Aulu s work  and tested against bad strings such as     -   -E-1   0-0   Here are my regex substring expr tools that seem to be holding up   parse num      local r  expr   1                 2 gt  dev null   tr -d   n     nat     -   0-9             dot    1         r   1             float       -      0-9   Ee   -      0-9           1      dot     amp  amp       1      float            1      nat        usage  parse num -123 456

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This is a little rough around the edges but a little more novice friendly   if    number -ge 0   then echo  Continue with code block  else echo  We matched 0 or  number is not a number  fi   This will cause an error and print  Illegal number   if  number is not a number but it will not break out of the script  Oddly there is not a test option I could find to just test for an integer  The logic here will match any number that is greater than or equal to 0

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bash regular expression vs bash parameter expansion  As Charles Duffy s answer work  but only use bash regular expression  and I know this to be slow  I would like to show another way  using only bash parameter expansion   For positive integers only   is num         1     amp  amp    -z    1   0-9           For integers   is num          local chk   1   -            chk     amp  amp    -z    chk   0-9          Then for floating   is num          local chk   1   -        chk   chk            chk     amp  amp    -z    chk   0-9          To match initial request   set --  foo bar  is num   1   amp  amp  VAR  1    echo  need a number  need a number  set --   3 141592  is num   1   amp  amp  VAR  1    echo  need a number   echo  VAR  3 141592   Now a little comparission   There is a same check based on Charles Duffy s answer   cdIs num          local re     -   0-9       0-9                1     re        Some tests   if is num foo then echo It  s a number  else echo Not a number fi Not a number if cdIs num foo then echo It  s a number  else echo Not a number fi Not a number if is num 25 then echo It  s a number  else echo Not a number fi It s a number if cdIs num 25 then echo It  s a number  else echo Not a number fi It s a number if is num 3 4 then echo It  s a number  else echo Not a number fi Not a number if cdIs num 3 4 then echo It  s a number  else echo Not a number fi Not a number if is num 3 1415 then echo It  s a number  else echo Not a number fi It s a number if cdIs num 3 1415 then echo It  s a number  else echo Not a number fi It s a number   Ok  that s fine  Now how many time will take all this  On my raspberry pi    time for i in  1  1000  do is num  3 14159265 done real    0m2 476s user    0m1 235s sys     0m0 000s   Then with regular expressions   time for i in  1  1000  do cdIs num  3 14159265 done real    0m4 363s user    0m2 168s sys     0m0 000s

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This can be achieved by using grep to see if the variable in question matches an extended regular expression   Test integer 1120   yournumber 1120 if echo   yournumber    grep -qE    0-9      then     echo  Valid number   else     echo  Error  not a number   fi   Output  Valid number   Test non-integer 1120a   yournumber 1120a if echo   yournumber    grep -qE    0-9      then     echo  Valid number   else     echo  Error  not a number   fi   Output  Error  not a number     Explanation   The grep  the -E switch allows us to use extended regular expression    0-9      This regular expression means the variable should only    contain the numbers 0-9 zero through nine from the   beginning to the   end of the variable and should have at least   one character  The grep  the -q quiet switch turns off any output whether or not it finds anything  if checks the exit status of grep  Exit status 0 means success and anything greater means an error  The grep command has an exit status of 0 if it finds a match and 1 when it doesn t    So putting it all together  in the if test  we echo the variable  yournumber and   pipe it to grep which with the -q switch silently matches the -E extended regular expression    0-9     expression  The exit status of grep will be 0 if grep successfully found a match and 1 if it didn t  If succeeded to match  we echo  Valid number    If it failed to match  we echo  Error  not a number       For Floats or Doubles  We can just change the regular expression from    0-9     to    0-9      0-9     for floats or doubles   Test float 1120 01   yournumber 1120 01 if echo   yournumber    grep -qE    0-9      0-9      then     echo  Valid number   else     echo  Error  not a number   fi   Output  Valid number   Test float 11 20 01   yournumber 11 20 01 if echo   yournumber    grep -qE    0-9      0-9      then     echo  Valid number   else     echo  Error  not a number   fi   Output  Error  not a number     For Negatives  To allow negative integers  just change the regular expression from    0-9     to    -  0-9       To allow negative floats or doubles  just change the regular expression from    0-9      0-9     to    -  0-9      0-9

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Stack popped a message asked me if I really want to answer after 30  answers  But of course    Use bash new features and here it is   after the comment I made a change      function isInt             1 -eq      1   0       2  dev null  amp  amp        1           amp  amp  echo 1     echo        function isInt             1      - 0-9         amp  amp      1 -eq      1   0       2 gt  dev null  amp  amp      1           amp  amp  echo 1     echo        Supports                  out-of-the-box                    1  negative integers  true  amp  arithmetic    2  positive integers  true  amp  arithmetic    3  with quotation  true  amp  arithmetic    4  without quotation  true  amp  arithmetic    5  all of the above with mixed signs       true  amp  arithmetic    6  empty string  false  amp  arithmetic    7  no value  false  amp  arithmetic    8  alphanumeric  false  amp  no arithmetic    9  mixed only signs  false  amp  no arithmetic                   problematic                      10  positive negative floats with 1 decimal  true  amp  NO arithmetic    11  positive negative floats with 2 or more decimals  FALSE  amp  NO arithmetic     True false is what you get from the function only when used combined with process substitution like in       isInt  lt arg gt       as there is no logical type in bash neither return value of function   I use capital when the result of the test expression is WRONG whereas  it should be the reverse   By  arithmetic  I mean bash can do math like in this expression   x      y   34      I use  arithmetic no arithmetic  when in mathematical expressions the argument acts as it is expected and  NO arithmetic  when it misbehaves compared with what it is expected   As you see  only no 10 and 11 are the problematic ones   Perfect   PS  Note that the MOST popular answer fails in case 9

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I use expr  It returns a non-zero if you try to add a zero to a non-numeric value   if expr --   number    0  gt   dev null 2 gt  amp 1 then     echo   number is a number  else     echo   number isn t a number  fi   It might be possible to use bc if you need non-integers  but I don t believe bc has quite the same behavior  Adding zero to a non-number gets you zero and it returns a value of zero too  Maybe you can combine bc and expr  Use bc to add zero to  number  If the answer is 0  then try expr to verify that  number isn t zero

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test -z    i   0-9     amp  amp  echo digits    echo no no no     i   0-9   replaces any digit in the value of  i with an empty string  see man -P  less   parameter    bash  -z checks if resulting string has zero length   if you also want to exclude the case when  i is empty  you could use one of these constructions   test -n   i   amp  amp  test -z    i   0-9     amp  amp  echo digits    echo not a number    -n   i   amp  amp  -z    i   0-9        amp  amp  echo digits    echo not a number

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As i had to tamper with this lately and like karttu s appoach with the unit test the most  I revised the code and added some other solutions too  try it out yourself to see the results      bin bash        N  0 1 2 3      by syntaxerror function isNaturalNumber           1       0-9               Z      -2 -1 0 1 2      by karttu function isInteger            1       -    0-9              Q      -   -   0 0            by karttu function isFloat            1       -      0-9      0-9      0-9      0-9     E  -      0-9               R      -1 -   -   0 E n       1      function isNumber      isNaturalNumber  1    isInteger  1    isFloat  1    bools   TRUE   FALSE   int values  0 123 -0 -123  float values  0 0 0   0 -0 0 -0  - 0       123 456 123   456 -123 456 -123  - 456       123 456E08 123 E08  456E08 -123 456E08 -123 E08 - 456E08       123 456E 08 123 E 08  456E 08 -123 456E 08 -123 E 08 - 456E 08       123 456E-08 123 E-08  456E-08 -123 456E-08 -123 E-08 - 456E-08  false values  blah meh mooh blah5 67mooh a123bc   for value in   int values    float values    false values  do     printf     5s  -30s    isNaturalNumber  value    bools        printf  isNaturalNumber  s    value      printf   5s  -24s    isInteger  value    bools        printf  isInteger  s    value      printf   5s  -24s    isFloat  value    bools        printf  isFloat  s    value      printf   5s  -24s n    isNumber  value    bools        printf  isNumber  s    value  done   So isNumber   includes dashes  commas and exponential notation and therefore returns TRUE on integers  amp  floats where on the other hand isFloat   returns FALSE on integer values and isInteger   likewise returns FALSE on floats  For your convenience all as one liners   isNaturalNumber          1       0-9          isInteger          1       -    0-9         isFloat          1       -      0-9      0-9      0-9      0-9     E  -      0-9          isNumber     isNaturalNumber  1    isInteger  1    isFloat  1

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The simplest way is to check whether it contains non-digit characters  You replace all digit characters with nothing and check for length  If there s length it s not a number   if      -n   input   0-9        then     echo  Input Is A Number  fi

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For my problem  I only needed to ensure that a user doesn t accidentally enter some text thus I tried to keep it simple and readable  isNumber             1    2 gt  dev null     According to the man page this pretty much does what I want     If the value of the expression is non-zero  the return status is 0   To prevent nasty error messages for strings that  might be numbers  I ignore the error output       2s    bash      2s  value too great for base  error token is  2s

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http   tldp org LDP Bash-Beginners-Guide html sect 04 03 html  You can also use bash s character classes   if     VAR       digit         then  echo   VAR is numeric  else  echo   VAR is not numeric  fi   Numerics will include space  the decimal point  and  e  or  E  for floating point   But  if you specify a C-style hex number  i e   0xffff  or  0XFFFF      digit    returns true   A bit of a trap here  bash allows you do to something like  0xAZ00  and still count it as a digit  isn t this from some weird quirk of GCC compilers that let you use 0x notation for bases other than 16      You might want to test for  0x  or  0X  before testing if it s a numeric if your input is completely untrusted  unless you want to accept hex numbers   That would be accomplished by   if      VARIABLE 1 2     0x             VARIABLE 1 2     0X      then echo   VAR is not numeric   fi

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I would try this   printf   g    var   amp  gt   dev null if          0      then     echo   var is a number   else     echo   var is not a number   fi   Note  this recognizes nan and inf as number

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Did the same thing here with a regular expression that test the entire part and decimals part  separated with a dot    re    0-9      0 1  0-9      if     1     re     then    echo  is numeric  else   echo  Naahh  not numeric  fi

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Following up on David W s answer from Oct  13  if using expr this might be better  test var  expr  am i numeric    0   gt  dev null 2 gt  amp 1 if     test var         then              If numeric  multiplied by 1 gives you the same value   including negative numbers    Otherwise you get null which you can test for

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Old question  but I just wanted to tack on my solution  This one doesn t require any strange shell tricks  or rely on something that hasn t been around forever   if   -n    printf   s n    var    sed  s  0-9   g       then     echo  is not numeric  else     echo  is numeric  fi   Basically it just removes all digits from the input  and if you re left with a non-zero-length string then it wasn t a number

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I use printf as other answers mentioned  if you supply the format string   f  or   i  printf will do the checking for you  Easier than reinventing the checks  the syntax is simple and short and printf is ubiquitous  So its a decent choice in my opinion - you can also use the following idea to check for a range of things  its not only useful for checking numbers    declare  -r CHECK FLOAT   f    declare  -r CHECK INTEGER   i          lt arg 1 gt  Number - Number to check        lt arg 2 gt  String - Number type to check        lt arg 3 gt  String - Error message   function check number        local NUMBER    1      local NUMBER TYPE    2      local ERROR MESG    3     local -i PASS 1    local -i FAIL 0      case    NUMBER TYPE   in         CHECK FLOAT             if       printf    CHECK FLOAT      NUMBER    amp  gt  dev random echo        then             echo    PASS           else             echo    ERROR MESG   1 gt  amp 2            echo    FAIL           fi                                     CHECK INTEGER             if       printf    CHECK INTEGER      NUMBER    amp  gt  dev random echo        then             echo    PASS           else             echo    ERROR MESG   1 gt  amp 2            echo    FAIL           fi                                                               echo  Invalid number type format    NUMBER TYPE  to check number     1 gt  amp 2         echo    FAIL                                  esac       gt   var 45   gt       check number  var    CHECK INTEGER    Error  Found  var - An integer is required       amp  amp    echo   var 5    bc

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1     -  0-9        amp  amp  echo  number    Don t forget - to include negative numbers

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One approach is to use a regular expression  like so   re    0-9     if       yournumber     re      then    echo  error  Not a number   gt  amp 2  exit 1 fi   If the value is not necessarily an integer  consider amending the regex appropriately  for instance     0-9       0-9           or  to handle numbers with a sign      -   0-9       0-9

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You could use  let  too like this          var 1       let  var  amp  amp  echo  It s a number     echo  It s not a number  It  s a number       var 01       let  var  amp  amp  echo  It s a number     echo  It s not a number  It  s a number       var toto       let  var  amp  amp  echo  It s a number     echo  It s not a number  It  s not a number          But I prefer use the      Bash 3  operator like some answers in this thread

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I use the following  for integers             constants         TRUE - true  0       FALSE - false  1     typeset -r   TRUE 0 typeset -r   FALSE 1     --------------------------------------    isNumber    check if a value is an integer     usage  isNumber testValue     returns      TRUE  - testValue is a number else not    function isNumber     typeset TESTVAR    echo   1    sed  s  0-9    g            TESTVAR  x     x    amp  amp  return     TRUE     return     FALSE     isNumber  1  if      -eq     TRUE      then   print  is a number  fi

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I m surprised at the solutions directly parsing number formats in shell  shell is not well suited to this  being a DSL for controlling files and processes  There are ample number parsers a little lower down  for example   isdecimal         filter octal hex ord     num   printf   s    1    sed  s  0    1-9     1   s           test   num   amp  amp  printf   f    num   gt  dev null 2 gt  amp 1     Change   f  to whatever particular format you require

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Quick  amp  Dirty  I know it s not the most elegant way  but I usually just added a zero to it and test the result  like so   function isInteger           1 0      0    amp  amp  echo   1 is a number     echo   1 is not a number      x 1       isInteger  x x  1      isInteger  x x  joe    isInteger  x x 0x16    isInteger  x x -32674  isInteger  x          1 0   will return 0 or bomb if  1 is NOT an integer  for Example   function zipIt      quick zip - unless the 1st parameter is a number   ERROR  not a valid number       if       1 0      0     then    isInteger  1         echo   backing up files changed in the last  1 days         OUT  zipIt- 1-day tgz         find   -mtime - 1 -type f -print0   xargs -0 tar cvzf  OUT        return 1   fi     showError  ERROR     NOTE  I guess I never thought to check for floats or mixed types that will make the entire script bomb    in my case  I didn t want it go any further  I m gonna play around with mrucci s solution and Duffy s regex - they seem the most robust within the bash framework

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To catch negative numbers   if     1      -    0-9           then     echo number else     echo not a number fi

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I found quite a short version   function isnum         return  echo   1    awk -F  n    print   0     0 0

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This tests if a number is a non negative integer and is both shell independent  i e  without bashisms  and uses only shell built-ins   INCORRECT    As this first answer  below  allows for integers with characters in them as long as the first are not first in the variable     -z    num   0-9        amp  amp  echo  is a number     echo  is not a number     CORRECT      As jilles commented and suggested in his answer this is the correct way to do it using shell-patterns       -z    num     0-9        amp  amp  echo  is a number     echo  is not a number

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I was looking at the answers and    realized that nobody thought about FLOAT numbers  with dot    Using grep is great too  -E means extended regexp -q means quiet  doesn t echo  -qE is the combination of both   To test directly in the command line     echo  32    grep -E   -  0-9      0-9        answer is  32    echo  3a2    grep -E   -  0-9      0-9        answer is empty  false     echo   5    grep -E   -  0-9      0-9        answer  5    echo  3 2    grep -E   -  0-9      0-9        answer is 3 2   Using in a bash script   check  echo   1    grep -E   -  0-9      0-9      if     check           then         it IS numeric   echo  Yeap   else     it is NOT numeric    echo  nooop  fi   To match JUST integers  use this     change check line to  check  echo   1    grep -E   -  0-9

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The following solution can also be used in basic shells such as Bourne without the need for regular expressions   Basically any numeric value evaluation operations using non-numbers will result in an error which will be implicitly considered as false in shell     var  -eq   var    as in      bin bash  var a  if   -n   var     amp  amp      var  -eq   var    2 gt  dev null  then   echo number else   echo not a number fi   You can can also test for    the return code of the operation which is more explicit     -n   var     amp  amp      var  -eq   var    2 gt  dev null if      -ne 0    then    echo  var is not number fi   Redirection of standard error is there to hide the  integer expression expected  message that bash prints out in case we do not have a number   CAVEATS  thanks to the comments below     Numbers with decimal points are not identified as valid  numbers  Using       instead of     will always evaluate to true Most non-Bash shells will always evaluate this expression as true The behavior in Bash is undocumented and may therefore change without warning If the value includes spaces after the number  e g   1 a   produces error  like bash      1 a  syntax error in expression  error token is  a   If the value is the same as var-name  e g  i  i    produces error  like bash      i  expression recursion level exceeded  error token is  i

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I like Alberto Zaccagni s answer   if     var  -eq   var    2 gt  dev null  then   Important prerequisites  - no subshells spawned - no RE parsers invoked - most shell applications don t use real numbers  But if  var is complex  e g  an associative array access   and if the number will be a non-negative integer  most use-cases   then this is perhaps more efficient   if     var  -ge 0   2 gt   dev null  then

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Without bashisms  works even in the System V sh    case  string in           0-9    echo bad           echo good    esac   This rejects empty strings and strings containing non-digits  accepting everything else   Negative or floating-point numbers need some additional work  An idea is to exclude -     in the first  bad  pattern and add more  bad  patterns containing the inappropriate uses of them    -

[linux] How do I test if a variable is a number in Bash?

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