Formatting the output of grep when matching on multiple files

grep

When searching on multiple files, the output of grep looks something like this:

{FILE}:{MATCH}

This is a problem since if I double-click on the {FILE} portion, I will at least also select (and copy) the : and possibly some of the match. How can I get grep to instead format its output something like this:

{FILE} : {MATCH}

Basically, I want to insert a space before the column. (and optionally one after)

Best Answer

grep -T will work 7/8ths of the time.

% for f in a ab abc abcd abcde abcdef abcdefg abcdefgh; do echo pattern > $f; done
% grep -T pattern *
a      :pattern
ab     :pattern
abc    :pattern
abcd   :pattern
abcde  :pattern
abcdef :pattern
abcdefg:pattern
abcdefgh       :pattern

From the GNU grep manual:

-T --initial-tab

Make sure that the first character of actual line content lies on a tab stop, so that the alignment of tabs looks normal. This is useful with options that prefix their output to the actual content: -H, -n, and -b. In order to improve the probability that lines from a single file will all start at the same column, this also causes the line number and byte offset (if present) to be printed in a minimum-size field width.

Related Solutions

Grep – How to Match Pattern Exactly from File and Search Only in First Column

You probably want the -wflag - from man grep

   -w, --word-regexp
          Select  only  those  lines  containing  matches  that form whole
          words.  The test is that the matching substring must  either  be
          at  the  beginning  of  the  line,  or  preceded  by  a non-word
          constituent character.  Similarly, it must be either at the  end
          of  the  line  or  followed by a non-word constituent character.
          Word-constituent  characters  are  letters,  digits,   and   the
          underscore.

i.e.

grep -wFf patfile file
denovo1 xxx yyyy oggugu ddddd
denovo22 hhhh yyyy kkkk iiii

To enforce matching only in the first column, you would need to modify the entries in the pattern file to add a line anchor: you could also make use of the \b word anchor instead of the command-line -w switch e.g. in patfile:

^denovo1\b
^denovo3\b
^denovo22\b

then

grep -f patfile file
denovo1 xxx yyyy oggugu ddddd
denovo22 hhhh yyyy kkkk iiii

Note that you must drop the -F switch if the file contains regular expressions instead of simple fixed strings.

How to split an output to two files with grep

There are many ways to accomplish this.

Using awk

The following sends any lines matching coolregex to file1. All other lines go to file2:

./mycommand.sh | awk '/[coolregex]/{print>"file1";next} 1' >file2

How it works:

/[coolregex]/{print>"file1";next}

Any lines matching the regular expression coolregex are printed to file1. Then, we skip all remaining commands and jump to start over on the next line.
1

All other lines are sent to stdout. 1 is awk's cryptic shorthand for print-the-line.

Splitting into multiple streams is also possible:

./mycommand.sh | awk '/regex1/{print>"file1"} /regex2/{print>"file2"} /regex3/{print>"file3"}'

Using process substitution

This is not as elegant as the awk solution but, for completeness, we can also use multiple greps combined with process substitution:

./mycommand.sh | tee >(grep 'coolregex' >File1) | grep -v 'coolregex' >File2

We can also split up into multiple streams:

./mycommand.sh | tee >(grep 'coolregex' >File1) >(grep 'otherregex' >File3) >(grep 'anotherregex' >File4) | grep -v 'coolregex' >File2