macOS bash script regular expression not working as expected

Question

I've been out of programming for more than 10 years. I have a text file that I'm trying to read the Mpbs value for the upload and download speed.

     Server: Iomart - Maidenhead (id = 3839)
        ISP: Plusnet
    Latency:     8.59 ms   (0.10 ms jitter)
   Download:    71.43 Mbps (data used: 52.8 MB)                               
     Upload:    18.39 Mbps (data used: 16.9 MB)                               
Packet Loss:     0.0%

I've been using a regex tool to test and build my regex, which delivers the result I want.

regex2="Upload:\W+([0-9]+\.[0-9]+)"
regex3="Download:\W+([0-9]+\.[0-9]+)"

while read line; do  
    if [[ $line =~ regex2 ]]
    then
        echo  "match ${BASH_REMATCH[1]}"
        UPS=${BASH_REMATCH[1]}
    fi  
    if [[ $line =~ regex3 ]]
    then
    echo  "match ${BASH_REMATCH[1]}"
        DNS=${BASH_REMATCH[1]}
    fi 
done < Result.txt

I'm sure there must be a better way to achieve what I want, but the main problem I'm having is the regex not working.

You are trying to match against the literal regex2 and regex3, I think you want $regex2 and $regex3. — jesse_b, Apr 08 '20 at 13:02
oops.. Thanks very much. That was a bad cut and paste. now the problem is the \W+ doesn't work. If i just leave the correct number of spaces(four in this case) in the regex2 variable it'll match. is \W or \s not the right way to go? i've tried using \ \ \\ and \\ — Stewart Rolfe, Apr 08 '20 at 13:13
\W is a PCRE feature - bash only claims to support ERE. I suspect that (especially on MacOS) the bash version doesn't recognize \W (or treats it as literal W). You could consider using [[:blank:]] instead to match horizontal whitespace (unless you specifically expect other non-word characters between the : and the number) — steeldriver, Apr 08 '20 at 13:27
... see also Why does my regular expression work in X but not in Y? — steeldriver, Apr 08 '20 at 13:28

Kusalananda · Answer 1 · 2020-04-08T15:25:32.637

0

You have three issues in your code.

You're not using the regular expressions you think you are (missing $ on regex2 and regex3).
bash does not understand the Perl-like regular expression \W as "not a word character".
You are not reading lines (even though your variable is called line).

To solve this:

Use $ on to get the values of regex2 and regex3 in the tests:
```
if [[ $line =~ $regex2 ]]; then ...; fi
```
Use the POSIX regular expression [^[:alnum:]_] in place of \W in the expressions, or [[:blank:]] which matches a tab or space.
Use while IFS= read -r line; do ...; done (see "Understanding "IFS= read -r line"").

edited Apr 08 '20 at 15:25

answered Apr 08 '20 at 15:17

Kusalananda

333,661

Thank you, one and all. – Stewart Rolfe Apr 09 '20 at 13:22
@StewartRolfe You may want to look at https://unix.stackexchange.com/help/someone-answers, and also take the tour: https://unix.stackexchange.com/tour (you'll receive a badge when you've done so). – Kusalananda Apr 09 '20 at 13:29

macOS bash script regular expression not working as expected

1 Answers1