Bash how to check if a string is a number(can be negative) [duplicate]

Question

I want to check if a certain string is a number, I tried this way:

if ${string} == *[!0-9]*
else echo its a number

but when I have a negative number, it says it's not a number, and i want it to work for negative numbers too.

In that question you can find some answers that take into account negative numbers. — fedorqui
– fedorqui, Commented Mar 24, 2014 at 12:57
@Sefi, the accepted answer there had a solution for negative numbers in its comments; I've edited it into the answer proper. — Charles Duffy
– Charles Duffy, Commented Mar 24, 2014 at 13:18
@CharlesDuffy Thanks a lot, but when I have a number like this "---7" it says it is not a number instead of reading it as -7 — Michael
– Michael, Commented Mar 24, 2014 at 13:38
@Sefi, ---7 isn't a number; the logic is correct. If you wanted zero-or-more - signs, though, you'd use -* instead of -?. By the way, the comments in the other answer discuss this too. :) — Charles Duffy
– Charles Duffy, Commented Mar 24, 2014 at 13:40

djm.im · Accepted Answer · 2014-03-24 16:55:45Z

3

Try this script

#!/bin/bash

string=$1

if [[ "$string" =~ ^(-)?[0-9]+$ ]]; then
  echo 'Number'
else
  echo 'Not number'
fi

This works only for integers.

If you want to match and decimal number then use this test

"$string" =~ ^-?[0-9]+(\.[0-9]+)?$

edited Mar 24, 2014 at 16:55

answered Mar 24, 2014 at 13:07

djm.im

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6 Comments

Jayesh Bhoi Over a year ago

+1 for what i think you paste here queckly

Michael Over a year ago

Thanks alot, but when I have number like this "---7" it says it is not a number.

djm.im Over a year ago

@Sefi you should have only one minus signe before number. If you want more than one minus signe then replace (-)? with (-)*

Michael Over a year ago

Thanks! Working perfectly!

mklement0 Over a year ago

In the decimal form you should replace * with ?, otherwise you'll also match input such as 1.2.3. (As an aside: I assume you used (-)? rather than just -? for readability.)

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