linux - [Solved-5 Solutions] How to test if a variable is a number in Bash - ubuntu - red hat - debian - linux server - linux pc
Linux - Problem :
Code:
test *isnumber* $1 && VAR=$1 || echo "need a number"click below button to copy the code. By - Linux tutorial - team
How to test if a variable is a number in Bash ?
Linux - Solution 1:
To use a regular expression, like this:
re='^[0-9]+$'
if ! [[ $yournumber =~ $re ]] ; then
echo "error: Not a number" >&2; exit 1
ficlick below button to copy the code. By - Linux tutorial - team
If the value is not necessarily an integer, consider amending the regex appropriately; for instance:
^[0-9]+([.][0-9]+)?$click below button to copy the code. By - Linux tutorial - team
To handle negative numbers:
^-?[0-9]+([.][0-9]+)?$click below button to copy the code. By - Linux tutorial - team
Linux - Solution 2:
case $string in
''|*[!0-9]*) echo bad ;;
*) echo good ;;
esacclick below button to copy the code. By - Linux tutorial - team
This rejects empty strings and strings containing non-digits, accepting everything else.
Negative or floating-point numbers need some additional work. An idea is to exclude - / . in the first "bad" pattern and add more "bad" patterns containing the inappropriate uses of them (?*-* / *.*.*)
Linux - Solution 3:
"$var" -eq "$var"click below button to copy the code. By - Linux tutorial - team
as in:
#!/bin/bash
var=a
if [ "$var" -eq "$var" ] 2>/dev/null; then
echo number
else
echo not a number
ficlick below button to copy the code. By - Linux tutorial - team
Redirection of standard error is there to hide the "integer expression expected" message that bash prints out in case we do not have a number.
- Numbers with decimal points are not identified as valid "numbers"
- Using [[ ]] instead of [ ] will always evaluate to true
- Most non-Bash shells will always evaluate this expression as true
- The behavior in Bash is undocumented and may therefore change without warning
- If value includes spaces after number (e.g. "1 a") produces error, like bash: [[: 1 a: syntax error in expression (error token is "a")
- If value is the same as var-name (e.g. i="i"), produces error, like bash: [[: i: expression recursion level exceeded (error token is "i")
Linux - Solution 4:
Solutions directly parsing number formats in shell. shell is not well suited to this, being a DSL for controlling files and processes. There are ample number parsers a little lower down, for example:
isdecimal() {
# filter octal/hex/ord()
num=$(printf '%s' "$1" | sed "s/^0*\([1-9]\)/\1/; s/'/^/")
test "$num" && printf '%f' "$num" >/dev/null 2>&1
}click below button to copy the code. By - Linux tutorial - team
Change '%f' to whatever particular format you require.
Linux - Solution 5:
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:
[ -z "${num##[0-9]*}" ] && echo "is a number" || echo "is not a number";click below button to copy the code. By - Linux tutorial - team
[ ! -z "${num##*[!0-9]*}" ] && echo "is a number" || echo "is not a number";