Re: [gentoo-user] bash script question

[Kerin Millar]

On 18/08/2014 12:29, Stroller wrote:
>
> On Mon, 18 August 2014, at 10:42 am, wraeth <wraeth@×××××××××.au> wrote:
>
>> On Mon, 2014-08-18 at 18:54 +1000, Adam Carter wrote:
>>> But this matches if grep fails both times as well as when it matches both
>>> time. Any ideas?
>>
>> If you don't mind using a quick loop, you could use something like:
>>
>> n=0
>> for f in file1.txt file2.txt file3.txt file4.txt; do
>>     grep 'string' ${f} >> /dev/null && n=$[n+1]
>> done
>>
>> if [[ $n == 4 ]]; then
>>     do_something
>> fi
>
> I've solved similar problems the same way myself, but I hope you'll forgive me for offering unsolicited critique on a small detail.
>
> In the above 4 is a constant, and thus it's independent of the number of files being tested.
>
> I propose addressing this with an array of the filenames.
>
> Thus additional files can be added for testing, without manual adjustment of the expected total.
>
>    files=("file1.txt" "file2.txt" "file3.txt" "file4.txt")
>    n=0
>    for f in ${files[@]}; do
>       grep 'string' ${f} >> /dev/null && n=$[n+1]

I would write `grep -q -m1 -F 'string' ...` here. In particular, -m1 
will short-circuit after finding one match.

>    done
>
>    if [[ $n == ${#files[@]} ]]; then
>       do_something
>    fi
>
> Bash array syntax is a bit arcane, but at least these very useful data structures are available.

Here's a slightly different take. It avoids multiple grep invocations, 
which could be a good thing in the case of a lengthy file list.

     files=(file1.txt file2.txt file3.txt file4.txt)
     string="matchme" # Using -F below as it's a string, not a regex

     count=0
     while read -r matches; do
         (( count += matches ))
     done < <(grep -hcm1 -F "$string" ${files[*]})

     if (( count == ${#files[@]} )); then
         do_something
     fi

--Kerin