In bash, if I want to execute a command and only display output lines that matches a certain pattern, I can pipe it to grep, like
file testfile
hello
there
my
friendscommand
$ cat testfile | grep 'hello'
hello #this will be highlightdthis will highlight the search match and display the entire line it falls on. I can use -A and -B to display lines before and after that line. My question is is it possible to execute the command and display all output as normal, but to highlight the search matches like grep would? so my ouput would be
hello #highlighted
there
my
friends6 Answers
To use a Color GREP to only highlight matched patterns but not otherwise change the output:
grep --color=always -e "^" -e "hello" testfileThe first pattern will match all lines (all lines will be printed) the second pattern (and any following patterns) cause the matched text to be highlighted in color.
Since the first pattern matches all lines but does not match on a printable character, it does not add any color highlighting so it doesn't compete/interfere with the readability of the highlighted text.
5Add option -z to your GNU grep command:
cat testfile | grep --color=always -z 'hello'or shorter
grep --color=always -z 'hello' testfileThis one works with GNU grep as well as with grep on FreeBSD:
grep --color=always 'hello\|$'It matches the text "hello" or (\|) the non-printable null string at the end of each line ($). That's why each line gets printed but only "hello" is highlighted.
Chances are you already have --color=auto configured in your shell. Then you most likely don't need to specify --color=always:
grep 'hello\|$'You can also simpler version by using egrep (with extended regular expressions), where | for the "or" expression doesn't need to be escaped:
egrep 'hello|$'Similarly to previous answer, you can catch all $ end of lines:
cat testfile | grep --color -E "hello|$"-E (or --extended-regexp) means that special characters must be escaped with \. When using it, | will be treated as regex "OR" condition.
Grep |$ will also catch and print all lines which has an end, but since $ is a hidden character, it cannot be highlighted.
Update:
If you'd like to print all output, but also return exit code, whether match was found or not, you can use perl command:
cat testfile | \
perl -pe 'BEGIN {$status=1} END {exit $status} $status=0 if /hello/;'If you prefer sed - Here's an example how to highlight all matches + return exit code if no match found:
Adding to the top answer above. The highlight{} function mentioned in the comments only works when data is piped into it. The following alias, while not perfect, is more useful:
alias greph="grep --color=always -e^ -e"This works with commands such as:
greph foo bar.txt
cat bar.txt | greph foo-z is good to output the entire file as in the answer from bot779 but most times you need to control how many lines you want to include above and below the match. You can control the length of context with -C <N> where N is the number of lines of context. See the example below:
cat >testfile <<EOM
hello
there
my
friends
more
lines
to demonstrate
context
EOM
cat testfile | grep --color=always -C 2 friends
there
my
*friends* highlighted
more
linesUsing a large number such as -C 1000 can also limit the output if the output you are filtering is too big.
