How to grep for lines containing either of two words, but not both

grep

I'm trying to use grep to show only lines containing either of the two words, if only one of them appears in the line, but not if they are in the same line.

So far I've tried grep pattern1 | grep pattern2 | ... but didn't get the result I expected.

Best Answer

A tool other than grep is the way to go.

Using perl, for instance, the command would be:

perl -ne 'print if /pattern1/ xor /pattern2/'

perl -ne runs the command given over each line of stdin, which in this case prints the line if it matches /pattern1/ xor /pattern2/, or in other words matches one pattern but not the other (exclusive or).

This works for the pattern in either order, and should have better performance than multiple invocations of grep, and is less typing as well.

Or, even shorter, with awk:

awk 'xor(/pattern1/,/pattern2/)'

or for versions of awk that don't have xor:

awk '/pattern1/+/pattern2/==1`

Related Solutions

Text Processing – How to Count Lines Containing One of Two Words but Not Both

With grep:

cat poem.txt \
  | grep -Evi -e '\<an\>.*\<the\>' -e '\<the\>.*\<an\>' \
  | grep -Eci -e '\<(an|the)\>'

This counts the matched lines. You can find an alternative syntax which counts the total number of matches down below.

Breakdown:

The frist grep command filters out all lines containing both 'an' and 'the'. The second grep command counts those lines, containing either 'an' or 'the'.

If you remove the c from the second grep's -Eci, you will see all matches highlighted.

Details:

The -E option enables extended expression syntax (ERE) for grep.
The -i option tells grep to match case-insensitive
The -v option tells grep to invert the result (i.e. match lines not containing the pattern)
The -c option tells grep to output the number of matched lines instead of the lines themselves
The patterns:
1. \< matches the beginning of a word (thanks @glenn-jackman)
2. \> matches the end of a word (thanks @glenn-jackman)
--> That way we can make sure to not match words containing 'the' or 'an' (like 'pan')
1. grep -Evi -e '\<an\>.*\<the\>' thus matches all lines not containing 'an ... the'
2. Similarly, grep -Evi -e '\<the\>.*\<an\>' matches all lines not containing 'the ... an'
3. grep -Evi -e '\<an\>.*\<the\>' -e '\<the.*an\>' is the combination of the 3. and 4.
4. grep -Eci -e '\<(an|the)\>' matches all lines containing either 'an' or 'the' (surrounded by whitespace or start/end of line) and prints the number of matched lines

EDIT 1: Use \< and \> instead of ( |^) and ( |$), as suggested by @glenn-jackman

EDIT 2: In order to count the number of matches instead of the number of matched lines, use the following expression:

cat poem.txt \
  | grep -Evi -e '\<an\>.*\<the\>' -e '\<the\>.*\<an\>' \
  | grep -Eio -e '\<(an|the)\>' \
  | wc -l

This uses the -o option of grep, which prints every match in a separate line (and nothing else) and then wc -l to count the lines.

Best Answer

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Text Processing – How to Count Lines Containing One of Two Words but Not Both

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