Display filename before matching line

If you have the options -H and -n available (man grep is your friend):

$ cat file
foo
bar
foobar

$ grep -H foo file
file:foo
file:foobar

$ grep -Hn foo file
file:1:foo
file:3:foobar

Options:

-H, --with-filename

Print the file name for each match. This is the default when there is more than one file to search.

-n, --line-number

Prefix each line of output with the 1-based line number within its input file. (-n is specified by POSIX.)

-H is a GNU extension, but -n is specified by POSIX

Try this little trick to coax grep into thinking it is dealing with multiple files, so that it displays the filename:

grep 'pattern' file /dev/null

To also get the line number:

grep -n 'pattern' file /dev/null

How about this, which I managed to achieve thanks, in part, to this post.

You want to find several files, lets say logs with different names but a pattern (e.g. filename=logfile.DATE), inside several directories with a pattern (e.g. /logsapp1, /logsapp2). Each file has a pattern you want to grep (e.g. "init time"), and you want to have the "init time" of each file, but knowing which file it belongs to.

find ./logsapp* -name logfile* | xargs -I{} grep "init time" {} \dev\null | tee outputfilename.txt

Then the outputfilename.txt would be something like

./logsapp1/logfile.22102015: init time: 10ms
./logsapp1/logfile.21102015: init time: 15ms
./logsapp2/logfile.21102015: init time: 17ms
./logsapp2/logfile.22102015: init time: 11ms

In general

find ./path_pattern/to_files* -name filename_pattern* | xargs -I{} grep "grep_pattern" {} \dev\null | tee outfilename.txt

Explanation:

find command will search the filenames based in the pattern

then, pipe xargs -I{} will redirect the find output to the {}

which will be the input for grep ""pattern" {}

Then the trick to make grep display the filenames \dev\null

and finally, write the output in file with tee outputfile.txt

This worked for me in grep version 9.0.5 build 1989.

No trick necessary.

grep --with-filename 'pattern' file

With line numbers:

grep -n --with-filename 'pattern' file