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2011-03-12 - Confoo 2011 presentation
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Check if variable is a number

Terminal - Check if variable is a number
if [ "$testnum" -eq "$testnum" 2>/dev/null ]; then echo It is numeric; fi
2009-10-09 14:57:27
User: jgc
Functions: echo
Check if variable is a number

Using the standard numeric comparison but suppressing the STDERR output acts as the simplest way to check a value is numeric. See sample output for some examples.


There is 1 alternative - vote for the best!

Terminal - Alternatives
if [[ "$1" =~ ^[0-9]+$ ]]; then echo "Is a number"; fi
(($1 > 0)) && echo "var is a number"
2013-03-22 01:15:00
User: khayyam
Functions: echo

calculate if "$1" is a number ... decimals included :)

echo $X | egrep "^[0-9]+$"

Know a better way?

If you can do better, submit your command here.

What others think

Try this.

export testnum=" " # a space

This will still echo out It is numeric.

Comment by uberwrensch 289 weeks and 3 days ago

Accepting space is a feature, since the Bash shell usually assumes null values are zero for arithmetic purposes. If that's not your purpose, then yeah this check isn't appropriate.

Comment by ashawley 289 weeks and 2 days ago

if you're talking about bash, and not plain sh:

[[ $testnum =~ ^[0-9]+$ ]] && echo is a number

yes -- that's a real regex. Dont put slashes around it (took me a while to realise that when I first tried this a few months ago!)

Comment by sitaram 289 weeks and 1 day ago

@sitaram: make that a command and I'll vote for it

Comment by ashawley 288 weeks and 6 days ago

Your point of view

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