simple? sh problen

[Ian Smith]

On Sun, 15 May 2005, Mikko Työläjärvi wrote:
 > On Mon, 16 May 2005, Ian Smith wrote:

 > > How do I test whether a sh argument is an integer or not, so as to avoid
 > > failing on a syntax error from otherwise working code such as:
 > >
 > > [ $3 -lt 10 -o $3 -gt 600 ] && echo "$0 $1 $2: $3 invalid" && exit 1
 > >
 > > when $3 is a non-integer argument?  Do I need to delve into awk and REs,
 > > or is there something more simple I've missed in mans test, expr, etc?
 > 
 > Here are some suggestions for functions to do the test:
 > 
 > isnum() {
 >      expr "$1" : '^[0-9][0-9]*$' >/dev/null
 > }
 > 
 > isnum() {
 >      case "$1" in
 >          *[^0-9]*|'') return 1;;
 >      esac
 >      return 0
 > }
 > 
 > The second one is likely to be faster unless "expr" is a shell builtin
 > (typically it it not).

Thanks Mikko; I liked the look of the case version, and it works fine:

if ! isnum $3; then echo "$0 $1 $2: $3 is not an integer"; exit 1; fi

 >     $.02,

Worth every penny.  Cheers, Ian