Related
I'm unable to get numeric comparisons working:
echo "enter two numbers";
read a b;
echo "a=$a";
echo "b=$b";
if [ $a \> $b ];
then
echo "a is greater than b";
else
echo "b is greater than a";
fi;
The problem is that it compares the number from the first digit on, i.e., 9 is bigger than 10, but 1 is greater than 09.
How can I convert the numbers into a type to do a true comparison?
In Bash, you should do your check in an arithmetic context:
if (( a > b )); then
...
fi
For POSIX shells that don't support (()), you can use -lt and -gt.
if [ "$a" -gt "$b" ]; then
...
fi
You can get a full list of comparison operators with help test or man test.
Like this:
#!/bin/bash
a=2462620
b=2462620
if [ "$a" -eq "$b" ]; then
echo "They're equal";
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.
There is also one nice thing some people might not know about:
echo $(( a < b ? a : b ))
This code will print the smallest number out of a and b
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 stuff like
(( (n + 1) > m ))
But everyone just has their own preferences. Sad thing is that some people impose their unofficial standards.
You can also do this:
[[ 'n + 1' -gt m ]]
Which allows you to add something else which you could do with [[ ]] besides arithmetic stuff.
The bracket stuff (e.g., [[ $a -gt $b ]] or (( $a > $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 <<< "...") )).
For example,
a=2.00
b=1
if (( $(bc <<<"$a > $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 (( $(bc <<<"$b == $c && $b < $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.
One-line solution.
a=2
b=1
[[ ${a} -gt ${b} ]] && echo "true" || echo "false"
gt reference: https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html
&& reference: https://www.gnu.org/software/bash/manual/html_node/Shell-Arithmetic.html
[[...]] construct reference: https://www.gnu.org/software/bash/manual/bash.html#index-_005b_005b
${} reference: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02 (2.6.2)
The format for parameter expansion is as follows:
${expression}
where expression consists of all characters until the matching '}'.
Any '}' escaped by a or within a quoted string, and
characters in embedded arithmetic expansions, command substitutions,
and variable expansions, shall not be examined in determining the
matching '}'.
The simplest form for parameter expansion is:
${parameter}
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 >= -1.2345) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
0
$ awk 'BEGIN {return_code=(-1.2345 < -1.2345) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
1
$ awk 'BEGIN {return_code=(-1.2345 < 2) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
0
$ awk 'BEGIN {return_code=(-1.2345 > 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 ">" 2 # returns false
# compare_nums 1.23 "<=" 2 # returns true
# compare_nums -1.238 "<=" -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 >&2 echo "$num1 is not a number"; return $E_BADARGS; fi
if ! [[ $num2 =~ ^-?[0-9]+([.][0-9]+)?$ ]]; then >&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 ">=" -1.2345 && echo true || echo false
true
$ compare_nums -1.2345 ">=" 23 && echo true || echo false
false
If you have floats, you can write a function and then use that. For example,
#!/bin/bash
function float_gt() {
perl -e "{if($1>$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
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 $val
}
This makes two important assumptions:
The input is a "normal SemVer string"
Each part is between 0-999
For example
versionToInt 12.34.56 # --> 12034056
versionToInt 1.2.3 # --> 1002003
Example testing whether npm command meets the minimum requirement...
NPM_ACTUAL=$(versionToInt $(npm --version)) # Capture npm version
NPM_REQUIRED=$(versionToInt 4.3.0) # Desired version
if [ $NPM_ACTUAL \< $NPM_REQUIRED ]; then
echo "Please update to npm#latest"
exit 1
fi
Just adding to all the above answers:
If you have more than one expression in single if statement, you can do something like this:
if (( $a % 2 == 0 )) && (( $b % 2 != 0));
then
echo "What you want to do"
fi
Hope this helps!
I'm unable to get numeric comparisons working:
echo "enter two numbers";
read a b;
echo "a=$a";
echo "b=$b";
if [ $a \> $b ];
then
echo "a is greater than b";
else
echo "b is greater than a";
fi;
The problem is that it compares the number from the first digit on, i.e., 9 is bigger than 10, but 1 is greater than 09.
How can I convert the numbers into a type to do a true comparison?
In Bash, you should do your check in an arithmetic context:
if (( a > b )); then
...
fi
For POSIX shells that don't support (()), you can use -lt and -gt.
if [ "$a" -gt "$b" ]; then
...
fi
You can get a full list of comparison operators with help test or man test.
Like this:
#!/bin/bash
a=2462620
b=2462620
if [ "$a" -eq "$b" ]; then
echo "They're equal";
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.
There is also one nice thing some people might not know about:
echo $(( a < b ? a : b ))
This code will print the smallest number out of a and b
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 stuff like
(( (n + 1) > m ))
But everyone just has their own preferences. Sad thing is that some people impose their unofficial standards.
You can also do this:
[[ 'n + 1' -gt m ]]
Which allows you to add something else which you could do with [[ ]] besides arithmetic stuff.
The bracket stuff (e.g., [[ $a -gt $b ]] or (( $a > $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 <<< "...") )).
For example,
a=2.00
b=1
if (( $(bc <<<"$a > $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 (( $(bc <<<"$b == $c && $b < $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.
One-line solution.
a=2
b=1
[[ ${a} -gt ${b} ]] && echo "true" || echo "false"
gt reference: https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html
&& reference: https://www.gnu.org/software/bash/manual/html_node/Shell-Arithmetic.html
[[...]] construct reference: https://www.gnu.org/software/bash/manual/bash.html#index-_005b_005b
${} reference: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02 (2.6.2)
The format for parameter expansion is as follows:
${expression}
where expression consists of all characters until the matching '}'.
Any '}' escaped by a or within a quoted string, and
characters in embedded arithmetic expansions, command substitutions,
and variable expansions, shall not be examined in determining the
matching '}'.
The simplest form for parameter expansion is:
${parameter}
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 >= -1.2345) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
0
$ awk 'BEGIN {return_code=(-1.2345 < -1.2345) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
1
$ awk 'BEGIN {return_code=(-1.2345 < 2) ? 0 : 1; exit} END {exit return_code}'
$ echo $?
0
$ awk 'BEGIN {return_code=(-1.2345 > 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 ">" 2 # returns false
# compare_nums 1.23 "<=" 2 # returns true
# compare_nums -1.238 "<=" -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 >&2 echo "$num1 is not a number"; return $E_BADARGS; fi
if ! [[ $num2 =~ ^-?[0-9]+([.][0-9]+)?$ ]]; then >&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 ">=" -1.2345 && echo true || echo false
true
$ compare_nums -1.2345 ">=" 23 && echo true || echo false
false
If you have floats, you can write a function and then use that. For example,
#!/bin/bash
function float_gt() {
perl -e "{if($1>$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
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 $val
}
This makes two important assumptions:
The input is a "normal SemVer string"
Each part is between 0-999
For example
versionToInt 12.34.56 # --> 12034056
versionToInt 1.2.3 # --> 1002003
Example testing whether npm command meets the minimum requirement...
NPM_ACTUAL=$(versionToInt $(npm --version)) # Capture npm version
NPM_REQUIRED=$(versionToInt 4.3.0) # Desired version
if [ $NPM_ACTUAL \< $NPM_REQUIRED ]; then
echo "Please update to npm#latest"
exit 1
fi
Just adding to all the above answers:
If you have more than one expression in single if statement, you can do something like this:
if (( $a % 2 == 0 )) && (( $b % 2 != 0));
then
echo "What you want to do"
fi
Hope this helps!
I would like to check if a string begins with "node" e.g. "node001". Something like
if [ $HOST == user* ]
then
echo yes
fi
How can I do it correctly?
I further need to combine expressions to check if HOST is either "user1" or begins with "node"
if [ [[ $HOST == user1 ]] -o [[ $HOST == node* ]] ];
then
echo yes
fi
> > > -bash: [: too many arguments
How can I do it correctly?
This snippet on the Advanced Bash Scripting Guide says:
# The == comparison operator behaves differently within a double-brackets
# test than within single brackets.
[[ $a == z* ]] # True if $a starts with a "z" (wildcard matching).
[[ $a == "z*" ]] # True if $a is equal to z* (literal matching).
So you had it nearly correct; you needed double brackets, not single brackets.
With regards to your second question, you can write it this way:
HOST=user1
if [[ $HOST == user1 ]] || [[ $HOST == node* ]] ;
then
echo yes1
fi
HOST=node001
if [[ $HOST == user1 ]] || [[ $HOST == node* ]] ;
then
echo yes2
fi
Which will echo
yes1
yes2
Bash's if syntax is hard to get used to (IMO).
If you're using a recent version of Bash (v3+), I suggest the Bash regex comparison operator =~, for example,
if [[ "$HOST" =~ ^user.* ]]; then
echo "yes"
fi
To match this or that in a regex, use |, for example,
if [[ "$HOST" =~ ^user.*|^host1 ]]; then
echo "yes"
fi
Note - this is 'proper' regular expression syntax.
user* means use and zero-or-more occurrences of r, so use and userrrr will match.
user.* means user and zero-or-more occurrences of any character, so user1, userX will match.
^user.* means match the pattern user.* at the begin of $HOST.
If you're not familiar with regular expression syntax, try referring to this resource.
Note that the Bash =~ operator only does regular expression matching when the right hand side is UNQUOTED. If you do quote the right hand side, "any part of the pattern may be quoted to force it to be matched as a string.". You should not quote the right hand side even when doing parameter expansion.
I always try to stick with POSIX sh instead of using Bash extensions, since one of the major points of scripting is portability (besides connecting programs, not replacing them).
In sh, there is an easy way to check for an "is-prefix" condition.
case $HOST in node*)
# Your code here
esac
Given how old, arcane and crufty sh is (and Bash is not the cure: It's more complicated, less consistent and less portable), I'd like to point out a very nice functional aspect: While some syntax elements like case are built-in, the resulting constructs are no different than any other job. They can be composed in the same way:
if case $HOST in node*) true;; *) false;; esac; then
# Your code here
fi
Or even shorter
if case $HOST in node*) ;; *) false;; esac; then
# Your code here
fi
Or even shorter (just to present ! as a language element -- but this is bad style now)
if ! case $HOST in node*) false;; esac; then
# Your code here
fi
If you like being explicit, build your own language element:
beginswith() { case $2 in "$1"*) true;; *) false;; esac; }
Isn't this actually quite nice?
if beginswith node "$HOST"; then
# Your code here
fi
And since sh is basically only jobs and string-lists (and internally processes, out of which jobs are composed), we can now even do some light functional programming:
beginswith() { case $2 in "$1"*) true;; *) false;; esac; }
checkresult() { if [ $? = 0 ]; then echo TRUE; else echo FALSE; fi; }
all() {
test=$1; shift
for i in "$#"; do
$test "$i" || return
done
}
all "beginswith x" x xy xyz ; checkresult # Prints TRUE
all "beginswith x" x xy abc ; checkresult # Prints FALSE
This is elegant. Not that I'd advocate using sh for anything serious -- it breaks all too quickly on real world requirements (no lambdas, so we must use strings. But nesting function calls with strings is not possible, pipes are not possible, etc.)
You can select just the part of the string you want to check:
if [ "${HOST:0:4}" = user ]
For your follow-up question, you could use an OR:
if [[ "$HOST" == user1 || "$HOST" == node* ]]
I prefer the other methods already posted, but some people like to use:
case "$HOST" in
user1|node*)
echo "yes";;
*)
echo "no";;
esac
Edit:
I've added your alternates to the case statement above
In your edited version you have too many brackets. It should look like this:
if [[ $HOST == user1 || $HOST == node* ]];
While I find most answers here quite correct, many of them contain unnecessary Bashisms. POSIX parameter expansion gives you all you need:
[ "${host#user}" != "${host}" ]
and
[ "${host#node}" != "${host}" ]
${var#expr} strips the smallest prefix matching expr from ${var} and returns that. Hence if ${host} does not start with user (node), ${host#user} (${host#node}) is the same as ${host}.
expr allows fnmatch() wildcards, thus ${host#node??} and friends also work.
Since # has a meaning in Bash, I got to the following solution.
In addition I like better to pack strings with "" to overcome spaces, etc.
A="#sdfs"
if [[ "$A" == "#"* ]];then
echo "Skip comment line"
fi
Adding a tiny bit more syntax detail to Mark Rushakoff's highest rank answer.
The expression
$HOST == node*
Can also be written as
$HOST == "node"*
The effect is the same. Just make sure the wildcard is outside the quoted text. If the wildcard is inside the quotes it will be interpreted literally (i.e. not as a wildcard).
#OP, for both your questions you can use case/esac:
string="node001"
case "$string" in
node*) echo "found";;
* ) echo "no node";;
esac
Second question
case "$HOST" in
node*) echo "ok";;
user) echo "ok";;
esac
case "$HOST" in
node*|user) echo "ok";;
esac
Or Bash 4.0
case "$HOST" in
user) ;&
node*) echo "ok";;
esac
if [ [[ $HOST == user1 ]] -o [[ $HOST == node* ]] ];
then
echo yes
fi
doesn't work, because all of [, [[, and test recognize the same nonrecursive grammar. See section CONDITIONAL EXPRESSIONS on your Bash man page.
As an aside, the SUSv3 says
The KornShell-derived conditional command (double bracket [[]]) was removed from the shell command language description in an early proposal. Objections were raised that the real problem is misuse of the test command ([), and putting it into the shell is the wrong way to fix the problem. Instead, proper documentation and a new shell reserved word (!) are sufficient.
Tests that require multiple test operations can be done at the shell level using individual invocations of the test command and shell logicals, rather than using the error-prone -o flag of test.
You'd need to write it this way, but test doesn't support it:
if [ $HOST == user1 -o $HOST == node* ];
then
echo yes
fi
test uses = for string equality, and more importantly it doesn't support pattern matching.
case / esac has good support for pattern matching:
case $HOST in
user1|node*) echo yes ;;
esac
It has the added benefit that it doesn't depend on Bash, and the syntax is portable. From the Single Unix Specification, The Shell Command Language:
case word in
[(]pattern1) compound-list;;
[[(]pattern[ | pattern] ... ) compound-list;;] ...
[[(]pattern[ | pattern] ... ) compound-list]
esac
grep
Forgetting performance, this is POSIX and looks nicer than case solutions:
mystr="abcd"
if printf '%s' "$mystr" | grep -Eq '^ab'; then
echo matches
fi
Explanation:
printf '%s' to prevent printf from expanding backslash escapes: Bash printf literal verbatim string
grep -q prevents echo of matches to stdout: How to check if a file contains a specific string using Bash
grep -E enables extended regular expressions, which we need for the ^
Keep it simple
word="appel"
if [[ $word = a* ]]
then
echo "Starts with a"
else
echo "No match"
fi
I tweaked #markrushakoff's answer to make it a callable function:
function yesNo {
# Prompts user with $1, returns true if response starts with y or Y or is empty string
read -e -p "
$1 [Y/n] " YN
[[ "$YN" == y* || "$YN" == Y* || "$YN" == "" ]]
}
Use it like this:
$ if yesNo "asfd"; then echo "true"; else echo "false"; fi
asfd [Y/n] y
true
$ if yesNo "asfd"; then echo "true"; else echo "false"; fi
asfd [Y/n] Y
true
$ if yesNo "asfd"; then echo "true"; else echo "false"; fi
asfd [Y/n] yes
true
$ if yesNo "asfd"; then echo "true"; else echo "false"; fi
asfd [Y/n]
true
$ if yesNo "asfd"; then echo "true"; else echo "false"; fi
asfd [Y/n] n
false
$ if yesNo "asfd"; then echo "true"; else echo "false"; fi
asfd [Y/n] ddddd
false
Here is a more complex version that provides for a specified default value:
function toLowerCase {
echo "$1" | tr '[:upper:]' '[:lower:]'
}
function yesNo {
# $1: user prompt
# $2: default value (assumed to be Y if not specified)
# Prompts user with $1, using default value of $2, returns true if response starts with y or Y or is empty string
local DEFAULT=yes
if [ "$2" ]; then local DEFAULT="$( toLowerCase "$2" )"; fi
if [[ "$DEFAULT" == y* ]]; then
local PROMPT="[Y/n]"
else
local PROMPT="[y/N]"
fi
read -e -p "
$1 $PROMPT " YN
YN="$( toLowerCase "$YN" )"
{ [ "$YN" == "" ] && [[ "$PROMPT" = *Y* ]]; } || [[ "$YN" = y* ]]
}
Use it like this:
$ if yesNo "asfd" n; then echo "true"; else echo "false"; fi
asfd [y/N]
false
$ if yesNo "asfd" n; then echo "true"; else echo "false"; fi
asfd [y/N] y
true
$ if yesNo "asfd" y; then echo "true"; else echo "false"; fi
asfd [Y/n] n
false
I'm trying to do something common enough: Parse user input in a shell script. If the user provided a valid integer, the script does one thing, and if not valid, it does something else. Trouble is, I haven't found an easy (and reasonably elegant) way of doing this - I don't want to have to pick it apart char by char.
I know this must be easy but I don't know how. I could do it in a dozen languages, but not BASH!
In my research I found this:
Regular expression to test whether a string consists of a valid real number in base 10
And there's an answer therein that talks about regex, but so far as I know, that's a function available in C (among others). Still, it had what looked like a great answer so I tried it with grep, but grep didn't know what to do with it. I tried -P which on my box means to treat it as a PERL regexp - nada. Dash E (-E) didn't work either. And neither did -F.
Just to be clear, I'm trying something like this, looking for any output - from there, I'll hack up the script to take advantage of whatever I get. (IOW, I was expecting that a non-conforming input returns nothing while a valid line gets repeated.)
snafu=$(echo "$2" | grep -E "/^[-+]?(?:\.[0-9]+|(?:0|[1-9][0-9]*)(?:\.[0-9]*)?)$/")
if [ -z "$snafu" ] ;
then
echo "Not an integer - nothing back from the grep"
else
echo "Integer."
fi
Would someone please illustrate how this is most easily done?
Frankly, this is a short-coming of TEST, in my opinion. It should have a flag like this
if [ -I "string" ] ;
then
echo "String is a valid integer."
else
echo "String is not a valid integer."
fi
[[ $var =~ ^-?[0-9]+$ ]]
The ^ indicates the beginning of the input pattern
The - is a literal "-"
The ? means "0 or 1 of the preceding (-)"
The + means "1 or more of the preceding ([0-9])"
The $ indicates the end of the input pattern
So the regex matches an optional - (for the case of negative numbers), followed by one or more decimal digits.
References:
http://www.tldp.org/LDP/abs/html/bashver3.html#REGEXMATCHREF
Wow... there are so many good solutions here!! Of all the solutions above, I agree with #nortally that using the -eq one liner is the coolest.
I am running GNU bash, version 4.1.5 (Debian). I have also checked this on ksh (SunSO 5.10).
Here is my version of checking if $1 is an integer or not:
if [ "$1" -eq "$1" ] 2>/dev/null
then
echo "$1 is an integer !!"
else
echo "ERROR: first parameter must be an integer."
echo $USAGE
exit 1
fi
This approach also accounts for negative numbers, which some of the other solutions will have a faulty negative result, and it will allow a prefix of "+" (e.g. +30) which obviously is an integer.
Results:
$ int_check.sh 123
123 is an integer !!
$ int_check.sh 123+
ERROR: first parameter must be an integer.
$ int_check.sh -123
-123 is an integer !!
$ int_check.sh +30
+30 is an integer !!
$ int_check.sh -123c
ERROR: first parameter must be an integer.
$ int_check.sh 123c
ERROR: first parameter must be an integer.
$ int_check.sh c123
ERROR: first parameter must be an integer.
The solution provided by Ignacio Vazquez-Abrams was also very neat (if you like regex) after it was explained. However, it does not handle positive numbers with the + prefix, but it can easily be fixed as below:
[[ $var =~ ^[-+]?[0-9]+$ ]]
Latecomer to the party here. I'm extremely surprised none of the answers mention the simplest, fastest, most portable solution; the case statement.
case ${variable#[-+]} in
*[!0-9]* | '') echo Not a number ;;
* ) echo Valid number ;;
esac
The trimming of any sign before the comparison feels like a bit of a hack, but that makes the expression for the case statement so much simpler.
I like the solution using the -eq test, because it's basically a one-liner.
My own solution was to use parameter expansion to throw away all the numerals and see if there was anything left. (I'm still using 3.0, haven't used [[ or expr before, but glad to meet them.)
if [ "${INPUT_STRING//[0-9]}" = "" ]; then
# yes, natural number
else
# no, has non-numeral chars
fi
For portability to pre-Bash 3.1 (when the =~ test was introduced), use expr.
if expr "$string" : '-\?[0-9]\+$' >/dev/null
then
echo "String is a valid integer."
else
echo "String is not a valid integer."
fi
expr STRING : REGEX searches for REGEX anchored at the start of STRING, echoing the first group (or length of match, if none) and returning success/failure. This is old regex syntax, hence the excess \. -\? means "maybe -", [0-9]\+ means "one or more digits", and $ means "end of string".
Bash also supports extended globs, though I don't recall from which version onwards.
shopt -s extglob
case "$string" of
#(-|)[0-9]*([0-9]))
echo "String is a valid integer." ;;
*)
echo "String is not a valid integer." ;;
esac
# equivalently, [[ $string = #(-|)[0-9]*([0-9])) ]]
#(-|) means "- or nothing", [0-9] means "digit", and *([0-9]) means "zero or more digits".
Here's yet another take on it (only using the test builtin command and its return code):
function is_int() { test "$#" -eq "$#" 2> /dev/null; }
input="-123"
if is_int "$input"
then
echo "Input: ${input}"
echo "Integer: ${input}"
else
echo "Not an integer: ${input}"
fi
You can strip non-digits and do a comparison. Here's a demo script:
for num in "44" "-44" "44-" "4-4" "a4" "4a" ".4" "4.4" "-4.4" "09"
do
match=${num//[^[:digit:]]} # strip non-digits
match=${match#0*} # strip leading zeros
echo -en "$num\t$match\t"
case $num in
$match|-$match) echo "Integer";;
*) echo "Not integer";;
esac
done
This is what the test output looks like:
44 44 Integer
-44 44 Integer
44- 44 Not integer
4-4 44 Not integer
a4 4 Not integer
4a 4 Not integer
.4 4 Not integer
4.4 44 Not integer
-4.4 44 Not integer
09 9 Not integer
For me, the simplest solution was to use the variable inside a (()) expression, as so:
if ((VAR > 0))
then
echo "$VAR is a positive integer."
fi
Of course, this solution is only valid if a value of zero doesn't make sense for your application. That happened to be true in my case, and this is much simpler than the other solutions.
As pointed out in the comments, this can make you subject to a code execution attack: The (( )) operator evaluates VAR, as stated in the Arithmetic Evaluation section of the bash(1) man page. Therefore, you should not use this technique when the source of the contents of VAR is uncertain (nor should you use ANY other form of variable expansion, of course).
or with sed:
test -z $(echo "2000" | sed s/[0-9]//g) && echo "integer" || echo "no integer"
# integer
test -z $(echo "ab12" | sed s/[0-9]//g) && echo "integer" || echo "no integer"
# no integer
Adding to the answer from Ignacio Vazquez-Abrams. This will allow for the + sign to precede the integer, and it will allow any number of zeros as decimal points. For example, this will allow +45.00000000 to be considered an integer.
However, $1 must be formatted to contain a decimal point. 45 is not considered an integer here, but 45.0 is.
if [[ $1 =~ ^-?[0-9]+.?[0]+$ ]]; then
echo "yes, this is an integer"
elif [[ $1 =~ ^\+?[0-9]+.?[0]+$ ]]; then
echo "yes, this is an integer"
else
echo "no, this is not an integer"
fi
For laughs I roughly just quickly worked out a set of functions to do this (is_string, is_int, is_float, is alpha string, or other) but there are more efficient (less code) ways to do this:
#!/bin/bash
function strindex() {
x="${1%%$2*}"
if [[ "$x" = "$1" ]] ;then
true
else
if [ "${#x}" -gt 0 ] ;then
false
else
true
fi
fi
}
function is_int() {
if is_empty "${1}" ;then
false
return
fi
tmp=$(echo "${1}" | sed 's/[^0-9]*//g')
if [[ $tmp == "${1}" ]] || [[ "-${tmp}" == "${1}" ]] ; then
#echo "INT (${1}) tmp=$tmp"
true
else
#echo "NOT INT (${1}) tmp=$tmp"
false
fi
}
function is_float() {
if is_empty "${1}" ;then
false
return
fi
if ! strindex "${1}" "-" ; then
false
return
fi
tmp=$(echo "${1}" | sed 's/[^a-z. ]*//g')
if [[ $tmp =~ "." ]] ; then
#echo "FLOAT (${1}) tmp=$tmp"
true
else
#echo "NOT FLOAT (${1}) tmp=$tmp"
false
fi
}
function is_strict_string() {
if is_empty "${1}" ;then
false
return
fi
if [[ "${1}" =~ ^[A-Za-z]+$ ]]; then
#echo "STRICT STRING (${1})"
true
else
#echo "NOT STRICT STRING (${1})"
false
fi
}
function is_string() {
if is_empty "${1}" || is_int "${1}" || is_float "${1}" || is_strict_string "${1}" ;then
false
return
fi
if [ ! -z "${1}" ] ;then
true
return
fi
false
}
function is_empty() {
if [ -z "${1// }" ] ;then
true
else
false
fi
}
Run through some tests here, I defined that -44 is an int but 44- isn't etc.. :
for num in "44" "-44" "44-" "4-4" "a4" "4a" ".4" "4.4" "-4.4" "09" "hello" "h3llo!" "!!" " " "" ; do
if is_int "$num" ;then
echo "INT = $num"
elif is_float "$num" ;then
echo "FLOAT = $num"
elif is_string "$num" ; then
echo "STRING = $num"
elif is_strict_string "$num" ; then
echo "STRICT STRING = $num"
else
echo "OTHER = $num"
fi
done
Output:
INT = 44
INT = -44
STRING = 44-
STRING = 4-4
STRING = a4
STRING = 4a
FLOAT = .4
FLOAT = 4.4
FLOAT = -4.4
INT = 09
STRICT STRING = hello
STRING = h3llo!
STRING = !!
OTHER =
OTHER =
NOTE: Leading 0's could infer something else when adding numbers such as octal so it would be better to strip them if you intend on treating '09' as an int (which I'm doing) (eg expr 09 + 0 or strip with sed)
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=$1 || echo "need a number"
Any help?
One approach is to use a regular expression, like so:
re='^[0-9]+$'
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]+)?$
Without bashisms (works even in the System V sh),
case $string in
''|*[!0-9]*) echo bad ;;
*) echo good ;;
esac
This rejects empty strings and strings containing non-digits, accepting everything else.
Negative or floating-point numbers need some additional work. An idea is to exclude - / . in the first "bad" pattern and add more "bad" patterns containing the inappropriate uses of them (?*-* / *.*.*)
The following solution can also be used in basic shells such as Bourne without the need for regular expressions. Basically any numeric value evaluation operations using non-numbers will result in an error which will be implicitly considered as false in shell:
"$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 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")
Nobody suggested bash's extended pattern matching:
[[ $1 == ?(-)+([0-9]) ]] && echo "$1 is an integer"
or using a POSIX character class:
[[ $1 == ?(-)+([[:digit:]]) ]] && echo "$1 is an integer"
This tests if a number is a non-negative integer. It is shell independent (i.e. without bashisms) and uses only shell built-ins:
[ ! -z "${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.
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.
Unsigned Integer is_uint()
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 bash integer capabilities
isuint_Bash() { (( 10#$1 >= 0 )) 2>/dev/null ;}
or better:
isuint_Bash() { set -- ${1//[+-]/.};(( 10#$1 >= 0 )) 2>/dev/null ;}
Using case
isuint_Case() { case $1 in ''|*[!0-9]*) return 1;;esac;}
Using bash's regex
isuint_Regx() { [[ $1 =~ ^[0-9]+$ ]] ;}
Signed integer is_int()
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 "${chk//[0-9]}" ] ;}
Using bash integer capabilities
isint_Bash() { set -- "${1//[!+-]}" ${1#${1//[!+-]}};
(( ( 0 ${1:-+} 10#$2 ) ? 1:1 )) 2>/dev/null ;}
Using case
isint_Case() { case ${1#[-+]} in ''|*[!0-9]*) return 1;;esac;}
Using bash's regex
isint_Regx() { [[ $1 =~ ^[+-]?[0-9]+$ ]] ;}
Number (unsigned float) is_num()
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 bash's regex
isnum_Regx() { [[ $1 =~ ^[+-]?([0-9]+([.][0-9]*)?|\.[0-9]+)$ ]] ;}
Using case
isnum_Case() { case ${1#[-+]} in ''|.|*[!0-9.]*|*.*.*) return 1;; esac ;}
Tests of concepts
(You could copy/paste this test code after previous declared functions.)
testcases=(
0 1 42 -3 +42 +3. .9 3.14 +3.141 -31.4 '' . 3-3 3.1.4 3a a3 blah 'Good day!'
);printf '%-12s %4s %4s %4s %4s %4s %4s %4s %4s %4s %4s %4s %4s\n' Value\\Func \
U{Prm,Grp,Bsh,Cse,Rgx} I{Prm,Bsh,Cse,Rgx} N{Prm,Cse,Rgx};\
for var in "${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+=' ##'
else
outstr+=' --'
fi
done
printf '%-11s %s\n' "$var" "$outstr"
done
Should output:
Value\Func UPrm UGrp UBsh UCse URgx IPrm IBsh ICse IRgx NPrm NCse NRgx
0 ## ## ## ## ## ## ## ## ## ## ## ##
1 ## ## ## ## ## ## ## ## ## ## ## ##
42 ## ## ## ## ## ## ## ## ## ## ## ##
-3 -- -- -- -- -- ## ## ## ## ## ## ##
+42 -- -- -- -- -- ## ## ## ## ## ## ##
+3. -- -- -- -- -- -- -- -- -- ## ## ##
.9 -- -- -- -- -- -- -- -- -- ## ## ##
3.14 -- -- -- -- -- -- -- -- -- ## ## ##
+3.141 -- -- -- -- -- -- -- -- -- ## ## ##
-31.4 -- -- -- -- -- -- -- -- -- ## ## ##
-- -- -- -- -- -- -- -- -- -- -- --
. -- -- -- -- -- -- -- -- -- -- -- --
3-3 -- -- -- -- -- -- ## -- -- -- -- --
3.1.4 -- -- -- -- -- -- -- -- -- -- -- --
3a -- -- -- -- -- -- -- -- -- -- -- --
a3 -- -- -- -- -- -- -- -- -- -- -- --
blah -- -- -- -- -- -- -- -- -- -- -- --
Good day! -- -- -- -- -- -- -- -- -- -- -- --
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
isuint_Case 6499µs 6566µs 13065µs 100.00%
isuint_Parm 26687µs 31600µs 58287µs 446.13%
isuint_Regx 36511µs 40181µs 76692µs 587.00%
isuint_Bash 43819µs 40311µs 84130µs 643.93%
isuint_Grep 1298265µs 1224112µs 2522377µs 19306.37%
Function Number NaN Total
isint_Case 22687µs 21914µs 44601µs 100.00%
isint_Parm 35765µs 34428µs 70193µs 157.38%
isint_Regx 36949µs 42319µs 79268µs 177.73%
isint_Bash 55368µs 65095µs 120463µs 270.09%
Function Number NaN Total
isnum_Case 23313µs 23446µs 46759µs 100.00%
isnum_Parm 35677µs 42169µs 77846µs 166.48%
isnum_Regx 51864µs 69502µs 121366µs 259.56%
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 than regex 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%% *}"
$shell < <(testScript) 2>&1 | xargs
done
This shows:
bash Success
dash Success
busybox Success
ksh Success
zsh Success
As I know other bash based solution like regex and bash's integer won't work in many other shells and forks are resource expensive, I would prefer the case way
(just before parameter expansion which is mostly compatible too).
I'm surprised at the solutions directly parsing number formats in shell.
shell is not well suited to this, being a DSL for controlling files and processes.
There are ample number parsers a little lower down, for example:
isdecimal() {
# filter octal/hex/ord()
num=$(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.
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 "$1" | grep -E ^\-?[0-9]+$`
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 "$n is not a number"
fi
test -z "${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
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")
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]+$' to '^\-?[0-9]*\.?[0-9]+$'.
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.
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.
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.
[[ $1 =~ ^-?[0-9]+$ ]] && echo "number"
Don't forget - to include negative numbers!
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" =~ $nat ]]
} # usage: parse_num -123.456
I use expr. It returns a non-zero if you try to add a zero to a non-numeric value:
if expr -- "$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.
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
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
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 $1; }
I use printf as other answers mentioned, if you supply the format string "%f" or "%i" printf will do the checking for you. Easier than reinventing the checks, the syntax is simple and short and printf is ubiquitous. So its a decent choice in my opinion - you can also use the following idea to check for a range of things, its not only useful for checking numbers.
declare -r CHECK_FLOAT="%f"
declare -r CHECK_INTEGER="%i"
## <arg 1> Number - Number to check
## <arg 2> String - Number type to check
## <arg 3> String - Error message
function check_number() {
local NUMBER="${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; }
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 ..
To catch negative numbers:
if [[ $1 == ?(-)+([0-9.]) ]]
then
echo number
else
echo not a number
fi
You could use "let" too like this :
[ ~]$ 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.
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
printf '%b' "-123\nABC" | tr '[:space:]' '_' | grep -q '^-\?[[:digit:]]\+$' && echo "Integer." || echo "NOT integer."
Remove the -\? in grep matching pattern if you don't accept negative integer.
Did the same thing here with a regular expression that test the entire part and decimals part, separated with a dot.
re="^[0-9]*[.]{0,1}[0-9]*$"
if [[ $1 =~ $re ]]
then
echo "is numeric"
else
echo "Naahh, not numeric"
fi
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
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