Re: problem with extended regular expression in bash 4.1

[Lawrence Steeger]

Alex Chupin (achupin <achupin <at> cisco.com> writes:

> 
> Dear All,
> 
> Can someone shed light on the difference in behaviour of bash 4.1. and 3.25? I
am out of ideas. 
> 
> Regards,
> Alexander Chupin
> 
> $ bash --version; s=12345;if [[ "$s" =~ '^[0-9]+$' ]]; then echo it is a
number; else echo it is NOT a number; fi
> GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
> Copyright (C) 2009 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> This is free software; you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.
> it is NOT a number
> 
> $ bash --version; s=12345;if [[ "$s" =~ '^[0-9]+$' ]]; then echo it is a
number; else echo it is NOT a number; fi
> GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)
> Copyright (C) 2005 Free Software Foundation, Inc.
> it is a number
> 
> 

The entire right side of '=~' is considered a regular expression.

The single quotes are being used in the match.  If you remove them,
it will work.

Another alternative is to assign the regular expression to a variable
and use it as the right side argument.