Result of grep can't be stored in variable

Question

I want to get a date from a file name. This works using this code:

for filename in OH/*
do
    echo $filename |grep -Eo '[[:digit:]]{14}'
done;

Now i want to save the result to a variable like this:

for filename in OH/*
do
    result=$($filename |grep -Eo '[[:digit:]]{14}')
    echo $result
done;

But i get 2 empty lines printed. What am i missing there?

Solution

You dropped the echo:

for filename in OH/*
do
    result=$(echo $filename | grep -Eo '[[:digit:]]{14}')
    echo "$result"
done;

or better yet,

for filename in OH/*
do
    result=$(printf %s "$filename" |grep -Eo '[[:digit:]]{14}')
    echo "$result"
done;

or

for filename in OH/*
do
    result=$(grep -Eo '[[:digit:]]{14}' <<<"$filename")
    echo "$result"
done;

Comments

[Kevin Lemaire]

Can you list the files to get filename exemple? Thanks.

[Kusalananda]

${filename:$((-21)):-7} (in bash) would also pick out the date stamp, if the file name suffix is always the same length.

[LaaKii]

It isn't always the same length. Thanks anyway!

[Kusalananda]

@ilkkachu Thanks! I was scratching my head over that, but not for long enough it seems :-)

[rien333]

Why not grep -Eo $filename '[[:digit:]]{14}'? Seems more portable than using <<< .

[Stephen Kitt]

rien333, that would look for the pattern $filename (or rather, the pattern corresponding to the value of the filename shell variable) in a file named [[:digit:]]{14}...

[done]

There is a clear chance that some other files will match the glob OH/* but not the grep regex. In such case, a NULL result will be printed. Avoid with `[ "$result" ] && echo "$result"

[done]

Quoting "$result" seems reasonable. Edit done.

[done]

No, it is not related to the empty (NULL) comment. That is why it is a separate comment. It is related to "quoting your expansions" as a reasonable good coding practice. I assumed you know it, that's why I directly did the edit. Better now? :-)

[Stephen Kitt]

@isaac right that makes sense, thanks for the edit. “Quoting "$result" seems reasonable” is the sort of thing I would write in the edit comment, not as a post comment ;-).