Bash regular expression not matching inside if

Question

I have a file /tmp/gish.dat which either contains a number (more than 0, and one or more digits) or nothing.

If there is a number present, I want my function to echo a # along with the number (eg #64). If there is no number present, I want my function to do nothing.

   get_issue() {
        if [ -f "/tmp/gish.dat" ]
        then
            iss=$(cat /tmp/gish.dat | grep -Eo '[0-9]+')
            if [[ iss =~ '[0-9]+' ]]
            then
              echo "#$iss"
            fi
        fi
    }

For some reason, the inner if never matches. Very new to bash.

Think you're missing a dollar symbol on your variable. Change it to $iss - in the if condition. — Benjamin Rowell, Mar 12 '17 at 13:03
Assuming your outer if works correctly, try printing the result of the shell call (iss) and check whether this worked correctly. EDIT: Pretty sure you are missing the dollar symbol, as benjamin already mentioned. — Julian Heinovski, Mar 12 '17 at 13:06
Maybe I also suggest you look at the -s option to test if the file is empty or not :) — grail, Mar 12 '17 at 15:17
Protip: [shellcheck](http://shellcheck.net) automatically detects issues like this — that other guy, Mar 12 '17 at 16:36

score 4 · Answer 1 · answered Mar 12 '17 at 13:52

4

If you qoute a regex within [[...]] it is only a string.

Replace '[0-9]+' by [0-9]+.

answered Mar 12 '17 at 13:52

Cyrus

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score 2 · Answer 2 · answered Mar 12 '17 at 13:10

You can rewrite your code this way:

   get_issue() {
        if [ -f "/tmp/gish.dat" ]
        then
            iss=$(grep -Eo '[0-9]+' /tmp/gish.dat)
            if [[ $iss ]]
            then
              echo "#$iss"
            fi
        fi
    }

Since grep -Eo extracts just the matching numeric part, there is no need to match the extracted string against the regex again in if. [[ $iss ]] is true whenever $iss is not empty.

score 0 · Answer 3 · answered Mar 14 '17 at 11:04

if you need to print something like #64, #45 etc then change your code as follows,

 if [ -f "/tmp/gish.dat" ]
    then
        iss=$(cat /tmp/gish.dat | grep -Eo '[0-9]+' | tr '\n' ' ')
        for isss in $iss    
        do  
                if [[ $isss =~ '[0-9]+' ]]
                then
                  echo "#$isss"
                fi  
        done;

fi

check out this one

Bash regular expression not matching inside if

3 Answers3