How to find patterns across multiple lines using grep?

Question

I want to find files that have \"abc\" AND \"efg\" in that order, and those two strings are on different lines in that file. Eg: a file with content:

blah bl         


        

Answer 1

awk one-liner:

awk '/abc/,/efg/' [file-with-content]

Answer 2

As an alternative to Balu Mohan's answer, it is possible to enforce the order of the patterns using only grep, head and tail:

for f in FILEGLOB; do tail $f -n +$(grep -n "pattern1" $f | head -n1 | cut -d : -f 1) 2>/dev/null | grep "pattern2" &>/dev/null && echo $f; done

This one isn't very pretty, though. Formatted more readably:

for f in FILEGLOB; do
    tail $f -n +$(grep -n "pattern1" $f | head -n1 | cut -d : -f 1) 2>/dev/null \
    | grep -q "pattern2" \
    && echo $f
done

This will print the names of all files where "pattern2" appears after "pattern1", or where both appear on the same line:

$ echo "abc
def" > a.txt
$ echo "def
abc" > b.txt
$ echo "abcdef" > c.txt; echo "defabc" > d.txt
$ for f in *.txt; do tail $f -n +$(grep -n "abc" $f | head -n1 | cut -d : -f 1) 2>/dev/null | grep -q "def" && echo $f; done
a.txt
c.txt
d.txt

Explanation

• tail -n +i - print all lines after the ith, inclusive
• grep -n - prepend matching lines with their line numbers
• head -n1 - print only the first row
• cut -d : -f 1 - print the first cut column using : as the delimiter
• 2>/dev/null - silence tail error output that occurs if the $() expression returns empty
• grep -q - silence grep and return immediately if a match is found, since we are only interested in the exit code

Answer 3

I'm not sure if it is possible with grep, but sed makes it very easy:

sed -e '/abc/,/efg/!d' [file-with-content]

Answer 4

This can be done easily by first using tr to replace the newlines with some other character:

tr '\n' '\a' | grep -o 'abc.*def' | tr '\a' '\n'

Here, I am using the alarm character, \a (ASCII 7) in place of a newline. This is almost never found in your text, and grep can match it with a ., or match it specifically with \a.

Answer 5

I released a grep alternative a few days ago that does support this directly, either via multiline matching or using conditions - hopefully it is useful for some people searching here. This is what the commands for the example would look like:

Multiline:

sift -lm 'abc.*efg' testfile

Conditions:

sift -l 'abc' testfile --followed-by 'efg'

You could also specify that 'efg' has to follow 'abc' within a certain number of lines:

sift -l 'abc' testfile --followed-within 5:'efg'

You can find more information on sift-tool.org.

Answer 6

This should work too?!

perl -lpne 'print $ARGV if /abc.*?efg/s' file_list

$ARGV contains the name of the current file when reading from file_list /s modifier searches across newline.