How do I test if a variable is a number in Bash?
LinuxBashShellLinux Problem Overview
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 && VAR=$1 || echo "need a number"
Any help?
Linux Solutions
Solution 1 - Linux
One approach is to use a regular expression, like so:
re='^[0-9]+$'
if ! [[ $yournumber =~ $re ]] ; then
echo "error: Not a number" >&2; exit 1
fi
If the value is not necessarily an integer, consider amending the regex appropriately; for instance:
^[0-9]+([.][0-9]+)?$
...or, to handle numbers with a sign:
^[+-]?[0-9]+([.][0-9]+)?$
Solution 2 - Linux
Without bashisms (works even in the System V sh),
case $string in
''|*[!0-9]*) echo bad ;;
*) echo good ;;
esac
This rejects empty strings and strings containing non-digits, accepting everything else.
Negative or floating-point numbers need some additional work. An idea is to exclude -
/ .
in the first "bad" pattern and add more "bad" patterns containing the inappropriate uses of them (?*-*
/ *.*.*
)
Solution 3 - Linux
The following solution can also be used in basic shells such as Bourne without the need for regular expressions. Basically any numeric value evaluation operations using non-numbers will result in an error which will be implicitly considered as false in shell:
"$var" -eq "$var"
as in:
#!/bin/bash
var=a
if [ -n "$var" ] && [ "$var" -eq "$var" ] 2>/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" ] && [ "$var" -eq "$var" ] 2>/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 totrue
- 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")
Solution 4 - Linux
Nobody suggested bash's extended pattern matching:
[[ $1 == ?(-)+([0-9]) ]] && echo "$1 is an integer"
or using new POSIX style:
[[ $1 == ?(-)+([:digit:]) ]] && echo "$1 is an integer"
Solution 5 - Linux
This tests if a number is a non-negative integer. It is shell independent (i.e. without bashisms) and uses only shell built-ins:
[ ! -z "${num##*[!0-9]*}" ] && echo "is a number" || echo "is not a number";
A previous version of this answer proposed:
[ -z "${num##[0-9]*}" ] && echo "is a number" || echo "is not a number";
but this is INCORRECT since it accepts any string starting with a digit, as jilles suggested.
Solution 6 - Linux
(2nd) Full rewrite of this answer: Jun 2021 27.
Some performance and compatibility hints
There are some strongly different methods regarding different kinds of tests.
I reviewed most relevant methods and built this comparison.
is_uint()
Unsigned Integer These functions implement code to assess whether an expression is an unsigned integer, i.e. consists entirely of digits.
-
Using parameter expansion
(This was my approach before all this!)
isuint_Parm() { [ "$1" ] && [ -z "${1//[0-9]}" ] ;}
-
Using fork to
grep
isuint_Grep() { grep -qE '^[0-9]+$' <<<"$1"; }
I test this method only once because it's very slow. This is just there to show what not to do.
-
Using [tag:bash] integer capabilities
isuint_Bash() { (( 10#$1 >= 0 )) 2>/dev/null ;}
-
Using
case
isuint_Case() { case $1 in ''|*[!0-9]*) return 1;;esac;}
-
Using [tag:bash]'s regex
isuint_Regx() { [[ $1 =~ ^[0-9]+$ ]] ;}
is_int()
Signed integer These functions implement code to assess whether an expression is a signed integer, i.e. as above but permitting an optional sign before the number.
-
Using parameter expansion
isint_Parm() { local chk=${1#[+-]}; [ "$chk" ] && [ -z "${chk//[0-9]}" ] ;}
-
Using [tag:bash] integer capabilities
isint_Bash() { (( 10#$1 )) 2>/dev/null ;}
-
Using
case
isint_Case() { case ${1#[-+]} in ''|*[!0-9]*) return 1;;esac;}
-
Using [tag:bash]'s regex
isint_Regx() { [[ $1 =~ ^[+-]?[0-9]+$ ]] ;}
is_num()
Number (unsigned float) These functions implement code to assess whether an expression is a floating-point number, i.e. as above but permitting an optional decimal point and additional digits after it. This does not attempt to cover numeric expressions in scientific notation (e.g. 1.0234E-12).
-
Using parameter expansion
isnum_Parm() { local ck=${1#[+-]};ck=${ck/.};[ "$ck" ]&&[ -z "${ck//[0-9]}" ];}
-
Using [tag:bash]'s regex
isnum_Regx() { [[ $1 =~ ^[+-]?([0-9]+([.][0-9]*)?|\.[0-9]+)$ ]] ;}
-
Using
case
isnum_Case() { case ${1#[-+]} in ''|.|*[!0-9.]*|*.*.*) return 1;; esac ;}
Tests of concepts
(You could copy/paste this test code after previous declared functions.)
testcases=(
1 42 -3 +42 +3. .9 3.14 +3.141 -31.4 '' . 3-3 3.1.4 3a a3 blah 'Good day!'
);printf '%-12s %4s %4s %4s %4s %4s %4s %4s %4s %4s %4s %4s %4s\n' Function \
U{Prm,Grp,Bsh,Cse,Rgx} I{Prm,Bsh,Cse,Rgx} N{Prm,Cse,Rgx}; \
for var in "${testcases[@]}";do
outstr='';
for func in isuint_{Parm,Grep,Bash,Case,Regx} isint_{Parm,Bash,Case,Regx} \
isnum_{Parm,Case,Regx};do
if $func "$var"
then outstr+=' num'
else outstr+=' str'
fi
done
printf '%-11s %s\n' "|$var|" "$outstr"
done
Should output:
Function UPrm UGrp UBsh UCse URgx IPrm IBsh ICse IRgx NPrm NCse NRgx
|1| num num num num num num num num num num num num
|42| num num num num num num num num num num num num
|-3| str str str str str num num num num num num num
|+42| str str num str str num num num num num num num
|+3.| str str str str str str str str str num num num
|.9| str str str str str str str str str num num num
|3.14| str str str str str str str str str num num num
|+3.141| str str str str str str str str str num num num
|-31.4| str str str str str str str str str num num num
|| str str num str str str str str str str str str
|.| str str str str str str str str str str str str
|3-3| str str num str str str str str str str str str
|3.1.4| str str str str str str str str str str str str
|3a| str str str str str str str str str str str str
|a3| str str str str str str str str str str str str
|blah| str str str str str str str str str str str str
|Good day!| str str str str str str str str str str str str
I hope! (Note: uint_bash
seem not perfect!)
Performance comparison
Then I've built this test function:
testFunc() {
local tests=1000 start=${EPOCHREALTIME//.}
for ((;tests--;)) ;do
"$1" "$3"
done
printf -v "$2" %u $((${EPOCHREALTIME//.}-start))
}
percent(){ local p=00$((${1}00000/$2));printf -v "$3" %.2f%% ${p::-3}.${p: -3};}
sortedTests() {
local func NaNTime NumTime ftyp="$1" nTest="$2" tTest="$3" min i pct line
local -a order=()
shift 3
for func ;do
testFunc "${ftyp}_$func" NaNTime "$tTest"
testFunc "${ftyp}_$func" NumTime "$nTest"
order[NaNTime+NumTime]=${ftyp}_$func\ $NumTime\ $NaNTime
done
printf '%-12s %11s %11s %14s\n' Function Number NaN Total
min="${!order[*]}" min=${min%% *}
for i in "${!order[@]}";do
read -ra line <<<"${order[i]}"
percent "$i" "$min" pct
printf '%-12s %9d\U00B5s %9d\U00B5s %12d\U00B5s %9s\n' \
"${line[@]}" "$i" "$pct"
done
}
I could run in this way:
sortedTests isuint "This is not a number." 31415926535897932384 \
Case Grep Parm Bash Regx ;\
sortedTests isint "This is not a number." 31415926535897932384 \
Case Parm Bash Regx ;\
sortedTests isnum "This string is clearly not a number..." \
3.141592653589793238462643383279502884 Case Parm Regx
On my host, this shows somthing like:
Function Number NaN Total Rank
isuint_Case 8,080µs 6,848µs 14,928µs 100.00%
isuint_Parm 10,571µs 13,061µs 23,632µs 158.31%
isuint_Regx 12,865µs 15,407µs 28,272µs 189.39%
isuint_Bash 19,054µs 17,182µs 36,236µs 242.74%
isuint_Grep 1,333,786µs 1,416,626µs 2,750,412µs 18424.52%
Function Number NaN Total Rank
isint_Case 8,860µs 7,813µs 16,673µs 100.00%
isint_Parm 14,141µs 16,774µs 30,915µs 185.42%
isint_Regx 14,202µs 17,375µs 31,577µs 189.39%
isint_Bash 18,988µs 16,598µs 35,586µs 213.43%
Function Number NaN Total Rank
isnum_Case 8,935µs 9,232µs 18,167µs 100.00%
isnum_Parm 18,898µs 22,577µs 41,475µs 228.30%
isnum_Regx 25,336µs 42,825µs 68,161µs 375.19%
You could download full isnum comparission script here or full isnum comparission script as text here., (with UTF8 and LATIN handling).
Conclusion
case
way is clearly the quickest! About 3x quicker thanregex
and 2x quicker than using parameter expansion.- forks (to
grep
or any binaries) are to be avoided when not needed.
case
method has become my favored choice:
is_uint() { case $1 in '' | *[!0-9]* ) return 1;; esac ;}
is_int() { case ${1#[-+]} in '' | *[!0-9]* ) return 1;; esac ;}
is_unum() { case $1 in '' | . | *[!0-9.]* | *.*.* ) return 1;; esac ;}
is_num() { case ${1#[-+]} in '' | . | *[!0-9.]* | *.*.* ) return 1;; esac ;}
About compatibility
For this, I wrote a little test script based on previous tests, with:
for shell in bash dash 'busybox sh' ksh zsh "$@";do
printf "%-12s " "${shell%% *}"
$shell < <(testScript) 2>&1 | xargs
done
This shows:
bash Success
dash Success
busybox Success
ksh Success
zsh Success
As I know other [tag:bash] based solution like regex and [tag:bash]'s integer won't work in many other shells and forks are resource expensive, I would prefer the case
way
(just before parameter expansion which is mostly compatible too).
Solution 7 - Linux
I'm surprised at the solutions directly parsing number formats in shell. shell is not well suited to this, being a DSL for controlling files and processes. There are ample number parsers a little lower down, for example:
isdecimal() {
# filter octal/hex/ord()
num=$(printf '%s' "$1" | sed "s/^0*\([1-9]\)/\1/; s/'/^/")
test "$num" && printf '%f' "$num" >/dev/null 2>&1
}
Change '%f' to whatever particular format you require.
Solution 8 - Linux
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 "$1" | grep -E ^\-?[0-9]+$`
Solution 9 - Linux
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 "$n is not a number"
fi
Solution 10 - Linux
test -z "${i//[0-9]}" && 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" && test -z "${i//[0-9]}" && echo digits || echo not a number
[[ -n "$i" && -z "${i//[0-9]}" ]] && echo digits || echo not a number
Solution 11 - Linux
This can be achieved by using grep
to see if the variable in question matches an extended regular expression.
1120
:
Test integer yournumber=1120
if echo "$yournumber" | grep -qE '^[0-9]+$'; then
echo "Valid number."
else
echo "Error: not a number."
fi
Output: Valid number.
1120a
:
Test non-integer yournumber=1120a
if echo "$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 numbers0-9
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 ofgrep
. Exit status0
means success and anything greater means an error. Thegrep
command has an exit status of0
if it finds a match and1
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.
1120.01
:
Test float 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.
11.20.01
:
Test float 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]+$'
to '^\-?[0-9]*\.?[0-9]+$'
.
Solution 12 - Linux
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>/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")
Solution 13 - Linux
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.
Solution 14 - Linux
[[ $1 =~ ^-?[0-9]+$ ]] && echo "number"
Don't forget -
to include negative numbers!
Solution 15 - Linux
I would try this:
printf "%g" "$var" &> /dev/null
if [[ $? == 0 ]] ; then
echo "$var is a number."
else
echo "$var is not a number."
fi
Note: this recognizes nan and inf as number.
Solution 16 - Linux
A clear answer has already been given by @charles Dufy and others. A pure bash solution would be using the following :
string="-12,345"
if [[ "$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>/dev/null | tr -d '\n'`
nat='^[+-]?[0-9]+[.,]?$' \
dot="${1%[.,]*}${r}${1##*[.,]}" \
float='^[\+\-]?([.,0-9]+[Ee]?[-+]?|)[0-9]+$'
[[ "$1" == $dot ]] && [[ "$1" =~ $float ]] || [[ "$1" =~ $nat ]]
} # usage: parse_num -123.456
Solution 17 - Linux
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 ${value}"
done
}
Notes: The isFloat pattern can be modified to be more tolerant about decimal point (@(.,)
) and the E symbol (@(Ee)
). My unit tests test only values that are either integer or float, but not any invalid input.
Solution 18 - Linux
I use expr. It returns a non-zero if you try to add a zero to a non-numeric value:
if expr -- "$number" + 0 > /dev/null 2>&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.
Solution 19 - Linux
One simple 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
Solution 20 - Linux
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={...,-½,-¼,0.0,¼,½,...} by karttu
function isFloat()
{
[[ ${1} == ?(-)@(+([0-9]).*([0-9])|*([0-9]).+([0-9]))?(E?(-|+)+([0-9])) ]]
}
# R={...,-1,-½,-¼,0.E+n,¼,½,1,...}
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 & 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; }
Solution 21 - Linux
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
Solution 22 - Linux
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"
## <arg 1> Number - Number to check
## <arg 2> String - Number type to check
## <arg 3> 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}" &>/dev/random;echo $?))); then
echo "${PASS}"
else
echo "${ERROR_MESG}" 1>&2
echo "${FAIL}"
fi
;;
"${CHECK_INTEGER}")
if ((! $(printf "${CHECK_INTEGER}" "${NUMBER}" &>/dev/random;echo $?))); then
echo "${PASS}"
else
echo "${ERROR_MESG}" 1>&2
echo "${FAIL}"
fi
;;
*)
echo "Invalid number type format: ${NUMBER_TYPE} to check_number()." 1>&2
echo "${FAIL}"
;;
esac
}
>$ var=45
>$ (($(check_number $var "${CHECK_INTEGER}" "Error: Found $var - An integer is required."))) && { echo "$var+5" | bc; }
Solution 23 - Linux
I like Alberto Zaccagni's answer.
if [ "$var" -eq "$var" ] 2>/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> /dev/null; then ..
Solution 24 - Linux
You could use "let" too like this :
[ ~]$ var=1
[ ~]$ let $var && echo "It's a number" || echo "It's not a number"
It\'s a number
[ ~]$ var=01
[ ~]$ let $var && echo "It's a number" || echo "It's not a number"
It\'s a number
[ ~]$ var=toto
[ ~]$ let $var && echo "It's a number" || echo "It's not a number"
It\'s not a number
[ ~]$
But I prefer use the "=~" Bash 3+ operator like some answers in this thread.
Solution 25 - Linux
Almost as you want in syntax. Just need a function isnumber
:
#!/usr/bin/bash
isnumber(){
num=$1
if [ -z "${num##*[!0-9]*}" ];
then return 1
else
return 0
fi
}
$(isnumber $1) && VAR=$1 || echo "need a number";
echo "VAR is $VAR"
test:
$ ./isnumtest 10
VAR is 10
$ ./isnumtest abc10
need a number
VAR is
Solution 26 - Linux
To catch negative numbers:
if [[ $1 == ?(-)+([0-9.]) ]]
then
echo number
else
echo not a number
fi
Solution 27 - Linux
printf '%b' "-123\nABC" | tr '[:space:]' '_' | grep -q '^-\?[[:digit:]]\+$' && echo "Integer." || echo "NOT integer."
Remove the -\?
in grep matching pattern if you don't accept negative integer.
Solution 28 - Linux
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
Solution 29 - Linux
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 ] && return ${__TRUE} || return ${__FALSE}
}
isNumber $1
if [ $? -eq ${__TRUE} ] ; then
print "is a number"
fi
Solution 30 - Linux
I tried ultrasawblade's recipe as it seemed the most practical to me, and couldn't make it work. In the end i devised another way though, based as others in parameter substitution, this time with regex replacement:
[[ "${var//*([[:digit:]])}" ]]; && 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.
Solution 31 - Linux
Quick & 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 ] && 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...
Solution 32 - Linux
I found quite a short version:
function isnum()
{
return `echo "$1" | awk -F"\n" '{print ($0 != $0+0)}'`
}
Solution 33 - Linux
-
variable to check
number=12345
ornumber=-23234
ornumber=23.167
ornumber=-345.234
-
check numeric or non-numeric
echo $number | grep -E '^-?[0-9]*\.?[0-9]*$' > /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
Solution 34 - Linux
Following up on David W's answer from Oct '13, if using expr
this might be better
test_var=`expr $am_i_numeric \* 0` >/dev/null 2>&1
if [ "$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
Solution 35 - Linux
Easy-to-understand and compatible solution, with test
command :
test $myVariable -eq 0 2>/dev/null
if [ $? -le 1 ]; then echo 'ok'; else echo 'KO'; fi
If myVariable = 0, the return code is 0
If myVariable > 0, the return code is 1
If myVariable is not an integer, the return code is 2
Solution 36 - Linux
The accepted answer didn't work for me in all cases BASH 4+ so :
# -- is var an integer? --
# trim leading/trailing whitespace, then check for digits return 0 or 1
# Globals: None
# Arguments: string
# Returns: boolean
# --
is_int() {
str="$(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" && echo "return 0" || echo "return 1"
Invalid (will return 1 = false) :
is_int "100abc" && echo "returned 0" || echo "returned 1"
is_int "" && echo "returned 0" || echo "returned 1"
is_int "100 100" && echo "returned 0" || echo "returned 1"
is_int " " && echo "returned 0" || echo "returned 1"
is_int $NOT_SET_VAR && echo "returned 0" || echo "returned 1"
is_int "3.14" && 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
Solution 37 - Linux
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
Solution 38 - Linux
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 &&
> [[ $1 != '' ]] && echo 1) || echo '' }
function isInt() {
([[ $1 =~ ^[-+0-9]+$ ]] && [[ $1 -eq $(( $1 + 0 )) ]] 2>/dev/null && [[ $1 != '' ]] && echo 1) || echo ''
}
Supports:
===============out-of-the-box==================
1. negative integers (true & arithmetic),
2. positive integers (true & arithmetic),
3. with quotation (true & arithmetic),
4. without quotation (true & arithmetic),
5. all of the above with mixed signs(!!!) (true & arithmetic),
6. empty string (false & arithmetic),
7. no value (false & arithmetic),
8. alphanumeric (false & no arithmetic),
9. mixed only signs (false & no arithmetic),
================problematic====================
10. positive/negative floats with 1 decimal (true & NO arithmetic),
11. positive/negative floats with 2 or more decimals (FALSE & NO arithmetic).
True/false is what you get from the function only when used combined with process substitution like in [[ $( isInt <arg> ) ]]
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!
Solution 39 - Linux
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.
Solution 40 - Linux
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 > 0) print $1; else print $1"*-1"}')
b=$(echo "scale=2;$a/$a + 1" | bc -l 2>/dev/null)
if [[ $b > 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