Regex "start of string" anchor not working - regex

Question

The regex I'm working with at the moment is as follows:
^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$
I'm trying to match all floating point numbers, but ONLY the number. For example, the following should match:
6.0
1.22E3
-2
2.99999e-12
However, the following should NOT match:
somestring///////6.0
I've tested the above regex on this validation site and it works as expected. When running it in my bash script, however, nothing at all matches.
This is my bash code:
if [[ "$VAL" =~ ^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$ ]]
then
echo $VAL, "is a number"
else
echo $VAL, "is not a number"
fi
I've tried removing the anchors, and it matches any strings that contain floating points. However, strings like "//////6.00007" match. The $ anchor works as expected; however, the ^ does not.
Please let me know if you have any suggestions for troubleshooting this issue.
Thanks!
Edit 1
Removed bad examples
Edit 2
I ran the regex in its own foo.sh as suggested by #lurker and the code ran as expected with my test cases. So I looked at what was being compared with the regex. When I echoed what was being compared, everything looked fine, so it made zero sense as to why the regex wasn't matching.
Then I began to suspect that echo wasn't displaying what was actually in $VAL for some reason.
So I ran this: NEWVAL=(echo $VAL) as a temporary workaround until I can figure out what's going on.

Answer 1

Your regex does not allow decimals in the exponent. Exponents may have decimals, so your either need to change your definition of what a 'number' is or you need to change your regex.
Assuming the later, here is a correction (Bash 4.4):
echo "6.0
1.22E3.7
-2
2.99999e-0.0001
somestring///////6.0" >/tmp/f1.txt
while IFS= read -r line || [[ -n $line ]]; do
if [[ "$line" =~ ^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[-+]?[0-9]*\.?[0-9]+)?$ ]]
then
echo $line, "is a number"
else
echo $line, "is not a number"
fi
done < /tmp/f1.txt
Prints:
6.0, is a number
1.22E3.7, is a number
-2, is a number
2.99999e-0.0001, is a number
somestring///////6.0, is not a number
BUT you should know, that most consider the only two legit numbers in your list to be 6.0 and -2. Easy way to test is with awk:
$ awk '$1+0==$1{print $0 " is a number"; next} {print $0 " not a number"}' /tmp/f1.txt
6.0 is a number
1.22E3.7 not a number
-2 is a number
2.99999e-0.0001 not a number
somestring///////6.0 not a number
The same C language function that awk uses to convert a string to a float is used by many other languages (Ruby, Perl, Python, C, C++, Swift, etc etc) so if you consider your format valid, you are probably going to be writing your own conversion routine as well.
For example, in most languages your can enter 10**1.5 as legit float literal. No language I know of accepts decimal numbers after the e in a string of the form 'xx.zzEyy.y'

Answer 2

As it turns out, the variables that I was comparing with my regex had leading newlines on them (e.g. "\n2.3333") that were being stripped away with echo. So, when I displayed the values to the screen with echo I would see the stripped version of my variable, which was not what was being compared with the regex.
Lesson learned: echo isn't always trustworthy. Per #CharlesDuffy's comment, use one of the following to see what's actually in your variables: declare -p varname or printf '%q\n' "$varname" but do not use echo $varname.