How do I grep for lines containing either of two words, but not both?

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.

edited Jan 31 at 3:22

Olorin

3,9481723

asked Jan 30 at 11:29

Trasmos

11613

(1) You talk about “words” and “patterns”. Which is it? Ordinary words like “quick”, “brown” and “fox”, or regular expressions like [a-z][a-z0-9](,7}(.[a-z0-9]{,3})+? (2) What if one of the words / patterns appears more than once in a line (and the other one doesn’t appear)? Is that equivalent to the word appearing once, or does it count as multiple occurrences?

– G-Man
Jan 31 at 4:05

add a comment |

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.

edited Jan 31 at 3:22

Olorin

3,9481723

asked Jan 30 at 11:29

Trasmos

11613

(1) You talk about “words” and “patterns”. Which is it? Ordinary words like “quick”, “brown” and “fox”, or regular expressions like [a-z][a-z0-9](,7}(.[a-z0-9]{,3})+? (2) What if one of the words / patterns appears more than once in a line (and the other one doesn’t appear)? Is that equivalent to the word appearing once, or does it count as multiple occurrences?

– G-Man
Jan 31 at 4:05

add a comment |

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.

edited Jan 31 at 3:22

Olorin

3,9481723

asked Jan 30 at 11:29

Trasmos

11613

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.

grep

edited Jan 31 at 3:22

Olorin

3,9481723

asked Jan 30 at 11:29

Trasmos

11613

edited Jan 31 at 3:22

Olorin

3,9481723

asked Jan 30 at 11:29

Trasmos

11613

edited Jan 31 at 3:22

Olorin

3,9481723

edited Jan 31 at 3:22

Olorin

3,9481723

edited Jan 31 at 3:22

Olorin

3,9481723

asked Jan 30 at 11:29

Trasmos

11613

asked Jan 30 at 11:29

Trasmos

11613

asked Jan 30 at 11:29

Trasmos

11613

(1) You talk about “words” and “patterns”. Which is it? Ordinary words like “quick”, “brown” and “fox”, or regular expressions like [a-z][a-z0-9](,7}(.[a-z0-9]{,3})+? (2) What if one of the words / patterns appears more than once in a line (and the other one doesn’t appear)? Is that equivalent to the word appearing once, or does it count as multiple occurrences?

– G-Man
Jan 31 at 4:05

add a comment |

(1) You talk about “words” and “patterns”. Which is it? Ordinary words like “quick”, “brown” and “fox”, or regular expressions like [a-z][a-z0-9](,7}(.[a-z0-9]{,3})+? (2) What if one of the words / patterns appears more than once in a line (and the other one doesn’t appear)? Is that equivalent to the word appearing once, or does it count as multiple occurrences?

– G-Man
Jan 31 at 4:05

(1) You talk about “words” and “patterns”. Which is it? Ordinary words like “quick”, “brown” and “fox”, or regular expressions like [a-z][a-z0-9](,7}(.[a-z0-9]{,3})+? (2) What if one of the words / patterns appears more than once in a line (and the other one doesn’t appear)? Is that equivalent to the word appearing once, or does it count as multiple occurrences?

– G-Man
Jan 31 at 4:05

add a comment |

6 Answers
6

active

oldest

votes

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`

edited Jan 30 at 16:29

answered Jan 30 at 12:03

Chris

1,160616

4

Nice - is the Awk xor available in GNU Awk only?

– steeldriver
Jan 30 at 13:29

9

@steeldriver I think it's GNU only, yes. Or at least it's missing on older versions. You can replace it with /pattern1/+/pattern2/==1 ir xor is missing.

– Chris
Jan 30 at 16:28

4

@JimL. You could put word boundaries (b) in the patterns themselves, i.e. bwordb.

– wjandrea
Jan 30 at 22:48

4

@vikingsteve If you specifically want to use grep, there are plenty of other answers here. But for people who just want to get the job done, it's good to know there are other tools that can do everything grep does, but more and more easily.

– Chris
Feb 1 at 11:04

3

@vikingsteve I would strongly suppose that the demand for a grep solution is a kind of XY problem

– Hagen von Eitzen
Feb 2 at 6:39

|
show 3 more comments

With GNU grep, you could pass both words to grep and then remove the lines containing both the patterns.

$ cat testfile.txt

abc

def

abc def

abc 123 def

1234

5678

1234 def abc

def abc



$ grep -w -e 'abc' -e 'def' testfile.txt | grep -v -e 'abc.*def' -e 'def.*abc'

abc

def

edited Jan 30 at 13:47

answered Jan 30 at 11:46

Haxiel

3,49811021

add a comment |

Try with egrep

egrep  'pattern1|pattern2' file | grep -v -e 'pattern1.*pattern2' -e 'pattern2.*pattern1'

edited Jan 30 at 14:56

answered Jan 30 at 11:45

msp9011

4,58044167

3

can also be written as grep -e foo -e bar | grep -v -e 'foo.*bar' -e 'bar.*foo'

– glenn jackman
Jan 30 at 13:40

8

Also, note from the grep man page: Direct invocation as either egrep or fgrep is deprecated -- prefer grep -E

– glenn jackman
Jan 30 at 13:41

That isn't in my OS @glennjackman

– Grump
Jan 30 at 15:14

1

@Grump really? What OS is that? Even POSIX mentions that grep should have -f and -e options although the older egrep and fgrep will continue to be supported for a while.

– terdon♦
Feb 1 at 18:22

1

@terdon, POSIX doesn't specify the path of the POSIX utilities. Again, there, the standard grep (that supports -F, -E, -e, -f as POSIX requires) is in /usr/xpg4/bin. The utilities in /bin are antiquated ones.

– Stéphane Chazelas
Feb 2 at 14:28

|
show 5 more comments

With grep implementations that support perl-like regular expressions (like pcregrep or GNU or ast-open grep -P), you can do it in one grep invocation with:

grep -P '^(?=.*pat1)(?!.*pat2)|^(?=.*pat2)(?!.*pat1)'

That is find the lines that match pat1 but not pat2, or pat2 but not pat1.

(?=...) and (?!...) are respectively look ahead and negative look ahead operators. So technically, the above looks for the beginning of the subject (^) provided it's followed by .*pat1 and not followed by .*pat2, or the same with pat1 and pat2 reversed.

That's suboptimal for lines that contain both patterns as they would then be looked for twice. You could instead use more advanced perl operators like:

grep -P '^(?=.*pat1|())(?(1)(?=.*pat2)|(?!.*pat2))'

(?(1)yespattern|nopattern) matches against yespattern if the 1^st capture group (empty () above) matched, and nopattern otherwise. If that () matches, that means pat1 didn't match, so we look for pat2 (positive look ahead), and we look for not pat2 otherwise (negative look ahead).

With sed, you could write it:

sed -ne '/pat1/{/pat2/!p;d;}' -e '/pat2/p'

edited Feb 1 at 14:08

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

Your first solution fails with grep: the -P option only supports a single pattern, at least on every system I have access to. +1 for your second solution, though.

– Chris
Jan 31 at 22:19

1

@Chris, you're right. That seems to be a limitation specific to GNU grep. pcregrep and ast-open grep don't have that problem. I've replaced the multiple -e with the alternation RE operator, so it should work with GNU grep as well now.

– Stéphane Chazelas
Jan 31 at 22:33

Yes, it works fine now.

– Chris
Jan 31 at 22:50

add a comment |

In Boolean terms, you're looking for A xor B, which can be written as

(A and not B)

(B and not A)

Given that your question doesn't mention that you are concerned with the order of the output so long as the matching lines are shown, the Boolean expansion of A xor B is pretty darn simple in grep:

$ cat << EOF > foo

> a b

> a

> b

> c a

> c b

> b a

> b c

> EOF

$ grep -w 'a' foo | grep -vw 'b'; grep -w 'b' foo | grep -vw 'a';

a

c a

b

c b

b c

edited Jan 30 at 23:42

answered Jan 30 at 20:58

Jim L.

1413

1

This works, but it will scramble the order of the file.

– Sparhawk
Jan 30 at 23:32

@Sparhawk True, although "scramble" is a harsh word. ;) it lists all the 'a' matches first, in order, then all the 'b' matches next, in order. The OP didn't express any interest in maintaining the order, just show the lines. FAWK, the next step could be sort | uniq.

– Jim L.
Jan 30 at 23:35

Fair call; I agree my language was inaccurate. I meant to imply that the original order would be changed.

– Sparhawk
Jan 30 at 23:43

1

@Sparhawk ... And I edited in your observation for full disclosure.

– Jim L.
Jan 30 at 23:44

add a comment |

-1

For the following example:

# Patterns:

#    apple

#    pear



# Example line

line="a_apple_apple_pear_a"

This can be done purely with grep -E, uniq, and wc.

# Grep for regex pattern, sort as unique, and count the number of lines

result=$(grep -oE 'apple|pear' <<< $line | sort -u | wc -l)

If grep is compiled with Perl regular expressions then you can match on the last occurrence instead of needing to pipe to uniq:

# Grep for regex pattern and count the number of lines

result=$(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l)

Output the result:

# Only one of the words exists if the result is < 2

((result > 0)) &&

   if (($result < 2)); then

      echo Only one word matched

   else

      echo Both words matched

   fi

A one-liner:

(($(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l) == 1)) && echo Only one word matched

If you don't want to hard-code the pattern, assembling it with a variable set of elements can be automated with a function.

This can also be done natively in Bash as a function without pipes or additional processes but would be more involved and is probably outside the scope of your question.

edited Jan 31 at 7:13

answered Jan 31 at 4:16

Zhro

375414

(1) I was wondering when somebody was going to give an answer using Perl regular expressions. If you focused on that part of your post, and explained how it worked, this could be a good answer. (2) But I’m afraid the rest isn’t so good. The question says “show only lines containing either of the two words” (emphasis added). If the output is supposed to be lines, then it stands to reason that the input must also be multiple lines. But your approach works only when looking at only a single line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … For example, if the input contains the lines Big applen and pear-shapedn, then the output should contain both of those lines. Your solution would get a count of 2; the long version would report “Both words matched” (which is an answer to the wrong question) and the short version would say nothing at all. (3) A suggestion: using -o here is a really bad idea, because it hides the lines that contain the matches, so you can’t see when both words appear on the same line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … (4) Bottom line: your use of uniq / sort -u and the fancy Perl regular expression to match only the last occurrence on each line don’t really add up to a useful answer to this question. But, even if they did, it would still be a bad answer because you don’t explain how they contribute to answering the question. (See Stéphane Chazelas’s answer for an example of a good explanation.)

– G-Man
Feb 2 at 23:35

The OP says that they wanted to "show only lines containing either of the two words" which means that each line has to be evaluated on its own. I don't see why you feel that this doesn't answer the question. Please provide an example input that you feel would fail.

– Zhro
Feb 2 at 23:46

Oh, is that what you meant? “Read the input a line at a time and execute these two or three commands for every line.”? (1) It’s painfully unclear that that’s what you meant. (2) It’s painfully inefficient. Four answers before yours showed how to handle the entire file in a few commands (one, two or four), and you want to run 3 × n commands for n lines of input? Even if it works, it earns a down vote for unnecessarily expensive execution. (3) At the risk of splitting hairs, it still doesn’t do the job of showing the appropriate lines.

– G-Man
Feb 3 at 1:09

|
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6 Answers
6

active

oldest

votes

6 Answers
6

active

oldest

votes

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/'

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`

edited Jan 30 at 16:29

answered Jan 30 at 12:03

Chris

1,160616

4

Nice - is the Awk xor available in GNU Awk only?

– steeldriver
Jan 30 at 13:29

9

@steeldriver I think it's GNU only, yes. Or at least it's missing on older versions. You can replace it with /pattern1/+/pattern2/==1 ir xor is missing.

– Chris
Jan 30 at 16:28

4

@JimL. You could put word boundaries (b) in the patterns themselves, i.e. bwordb.

– wjandrea
Jan 30 at 22:48

4

@vikingsteve If you specifically want to use grep, there are plenty of other answers here. But for people who just want to get the job done, it's good to know there are other tools that can do everything grep does, but more and more easily.

– Chris
Feb 1 at 11:04

3

@vikingsteve I would strongly suppose that the demand for a grep solution is a kind of XY problem

– Hagen von Eitzen
Feb 2 at 6:39

|
show 3 more comments

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/'

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`

edited Jan 30 at 16:29

answered Jan 30 at 12:03

Chris

1,160616

4

Nice - is the Awk xor available in GNU Awk only?

– steeldriver
Jan 30 at 13:29

9

@steeldriver I think it's GNU only, yes. Or at least it's missing on older versions. You can replace it with /pattern1/+/pattern2/==1 ir xor is missing.

– Chris
Jan 30 at 16:28

4

@JimL. You could put word boundaries (b) in the patterns themselves, i.e. bwordb.

– wjandrea
Jan 30 at 22:48

4

@vikingsteve If you specifically want to use grep, there are plenty of other answers here. But for people who just want to get the job done, it's good to know there are other tools that can do everything grep does, but more and more easily.

– Chris
Feb 1 at 11:04

3

@vikingsteve I would strongly suppose that the demand for a grep solution is a kind of XY problem

– Hagen von Eitzen
Feb 2 at 6:39

|
show 3 more comments

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/'

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`

edited Jan 30 at 16:29

answered Jan 30 at 12:03

Chris

1,160616

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/'

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`

edited Jan 30 at 16:29

answered Jan 30 at 12:03

Chris

1,160616

edited Jan 30 at 16:29

answered Jan 30 at 12:03

Chris

1,160616

answered Jan 30 at 12:03

Chris

1,160616

answered Jan 30 at 12:03

Chris

1,160616

4

Nice - is the Awk xor available in GNU Awk only?

– steeldriver
Jan 30 at 13:29

9

@steeldriver I think it's GNU only, yes. Or at least it's missing on older versions. You can replace it with /pattern1/+/pattern2/==1 ir xor is missing.

– Chris
Jan 30 at 16:28

4

@JimL. You could put word boundaries (b) in the patterns themselves, i.e. bwordb.

– wjandrea
Jan 30 at 22:48

4

@vikingsteve If you specifically want to use grep, there are plenty of other answers here. But for people who just want to get the job done, it's good to know there are other tools that can do everything grep does, but more and more easily.

– Chris
Feb 1 at 11:04

3

@vikingsteve I would strongly suppose that the demand for a grep solution is a kind of XY problem

– Hagen von Eitzen
Feb 2 at 6:39

|
show 3 more comments

4

Nice - is the Awk xor available in GNU Awk only?

– steeldriver
Jan 30 at 13:29

9

@steeldriver I think it's GNU only, yes. Or at least it's missing on older versions. You can replace it with /pattern1/+/pattern2/==1 ir xor is missing.

– Chris
Jan 30 at 16:28

4

@JimL. You could put word boundaries (b) in the patterns themselves, i.e. bwordb.

– wjandrea
Jan 30 at 22:48

4

@vikingsteve If you specifically want to use grep, there are plenty of other answers here. But for people who just want to get the job done, it's good to know there are other tools that can do everything grep does, but more and more easily.

– Chris
Feb 1 at 11:04

3

@vikingsteve I would strongly suppose that the demand for a grep solution is a kind of XY problem

– Hagen von Eitzen
Feb 2 at 6:39

Nice - is the Awk xor available in GNU Awk only?

– steeldriver
Jan 30 at 13:29

@steeldriver I think it's GNU only, yes. Or at least it's missing on older versions. You can replace it with /pattern1/+/pattern2/==1 ir xor is missing.

– Chris
Jan 30 at 16:28

@JimL. You could put word boundaries (b) in the patterns themselves, i.e. bwordb.

– wjandrea
Jan 30 at 22:48

@vikingsteve If you specifically want to use grep, there are plenty of other answers here. But for people who just want to get the job done, it's good to know there are other tools that can do everything grep does, but more and more easily.

– Chris
Feb 1 at 11:04

@vikingsteve I would strongly suppose that the demand for a grep solution is a kind of XY problem

– Hagen von Eitzen
Feb 2 at 6:39

|
show 3 more comments

With GNU grep, you could pass both words to grep and then remove the lines containing both the patterns.

$ cat testfile.txt

abc

def

abc def

abc 123 def

1234

5678

1234 def abc

def abc



$ grep -w -e 'abc' -e 'def' testfile.txt | grep -v -e 'abc.*def' -e 'def.*abc'

abc

def

edited Jan 30 at 13:47

answered Jan 30 at 11:46

Haxiel

3,49811021

add a comment |

With GNU grep, you could pass both words to grep and then remove the lines containing both the patterns.

$ cat testfile.txt

abc

def

abc def

abc 123 def

1234

5678

1234 def abc

def abc



$ grep -w -e 'abc' -e 'def' testfile.txt | grep -v -e 'abc.*def' -e 'def.*abc'

abc

def

edited Jan 30 at 13:47

answered Jan 30 at 11:46

Haxiel

3,49811021

add a comment |

With GNU grep, you could pass both words to grep and then remove the lines containing both the patterns.

$ cat testfile.txt

abc

def

abc def

abc 123 def

1234

5678

1234 def abc

def abc



$ grep -w -e 'abc' -e 'def' testfile.txt | grep -v -e 'abc.*def' -e 'def.*abc'

abc

def

edited Jan 30 at 13:47

answered Jan 30 at 11:46

Haxiel

3,49811021

With GNU grep, you could pass both words to grep and then remove the lines containing both the patterns.

$ cat testfile.txt

abc

def

abc def

abc 123 def

1234

5678

1234 def abc

def abc



$ grep -w -e 'abc' -e 'def' testfile.txt | grep -v -e 'abc.*def' -e 'def.*abc'

abc

def

edited Jan 30 at 13:47

answered Jan 30 at 11:46

Haxiel

3,49811021

edited Jan 30 at 13:47

answered Jan 30 at 11:46

Haxiel

3,49811021

answered Jan 30 at 11:46

Haxiel

3,49811021

answered Jan 30 at 11:46

Haxiel

3,49811021

add a comment |

Try with egrep

egrep  'pattern1|pattern2' file | grep -v -e 'pattern1.*pattern2' -e 'pattern2.*pattern1'

edited Jan 30 at 14:56

answered Jan 30 at 11:45

msp9011

4,58044167

3

can also be written as grep -e foo -e bar | grep -v -e 'foo.*bar' -e 'bar.*foo'

– glenn jackman
Jan 30 at 13:40

8

Also, note from the grep man page: Direct invocation as either egrep or fgrep is deprecated -- prefer grep -E

– glenn jackman
Jan 30 at 13:41

That isn't in my OS @glennjackman

– Grump
Jan 30 at 15:14

1

@Grump really? What OS is that? Even POSIX mentions that grep should have -f and -e options although the older egrep and fgrep will continue to be supported for a while.

– terdon♦
Feb 1 at 18:22

1

@terdon, POSIX doesn't specify the path of the POSIX utilities. Again, there, the standard grep (that supports -F, -E, -e, -f as POSIX requires) is in /usr/xpg4/bin. The utilities in /bin are antiquated ones.

– Stéphane Chazelas
Feb 2 at 14:28

|
show 5 more comments

Try with egrep

egrep  'pattern1|pattern2' file | grep -v -e 'pattern1.*pattern2' -e 'pattern2.*pattern1'

edited Jan 30 at 14:56

answered Jan 30 at 11:45

msp9011

4,58044167

3

can also be written as grep -e foo -e bar | grep -v -e 'foo.*bar' -e 'bar.*foo'

– glenn jackman
Jan 30 at 13:40

8

Also, note from the grep man page: Direct invocation as either egrep or fgrep is deprecated -- prefer grep -E

– glenn jackman
Jan 30 at 13:41

That isn't in my OS @glennjackman

– Grump
Jan 30 at 15:14

1

@Grump really? What OS is that? Even POSIX mentions that grep should have -f and -e options although the older egrep and fgrep will continue to be supported for a while.

– terdon♦
Feb 1 at 18:22

1

@terdon, POSIX doesn't specify the path of the POSIX utilities. Again, there, the standard grep (that supports -F, -E, -e, -f as POSIX requires) is in /usr/xpg4/bin. The utilities in /bin are antiquated ones.

– Stéphane Chazelas
Feb 2 at 14:28

|
show 5 more comments

Try with egrep

egrep  'pattern1|pattern2' file | grep -v -e 'pattern1.*pattern2' -e 'pattern2.*pattern1'

edited Jan 30 at 14:56

answered Jan 30 at 11:45

msp9011

4,58044167

Try with egrep

egrep  'pattern1|pattern2' file | grep -v -e 'pattern1.*pattern2' -e 'pattern2.*pattern1'

edited Jan 30 at 14:56

answered Jan 30 at 11:45

msp9011

4,58044167

edited Jan 30 at 14:56

answered Jan 30 at 11:45

msp9011

4,58044167

answered Jan 30 at 11:45

msp9011

4,58044167

answered Jan 30 at 11:45

msp9011

4,58044167

3

can also be written as grep -e foo -e bar | grep -v -e 'foo.*bar' -e 'bar.*foo'

– glenn jackman
Jan 30 at 13:40

8

Also, note from the grep man page: Direct invocation as either egrep or fgrep is deprecated -- prefer grep -E

– glenn jackman
Jan 30 at 13:41

That isn't in my OS @glennjackman

– Grump
Jan 30 at 15:14

1

@Grump really? What OS is that? Even POSIX mentions that grep should have -f and -e options although the older egrep and fgrep will continue to be supported for a while.

– terdon♦
Feb 1 at 18:22

1

@terdon, POSIX doesn't specify the path of the POSIX utilities. Again, there, the standard grep (that supports -F, -E, -e, -f as POSIX requires) is in /usr/xpg4/bin. The utilities in /bin are antiquated ones.

– Stéphane Chazelas
Feb 2 at 14:28

|
show 5 more comments

3

can also be written as grep -e foo -e bar | grep -v -e 'foo.*bar' -e 'bar.*foo'

– glenn jackman
Jan 30 at 13:40

8

Also, note from the grep man page: Direct invocation as either egrep or fgrep is deprecated -- prefer grep -E

– glenn jackman
Jan 30 at 13:41

That isn't in my OS @glennjackman

– Grump
Jan 30 at 15:14

1

@Grump really? What OS is that? Even POSIX mentions that grep should have -f and -e options although the older egrep and fgrep will continue to be supported for a while.

– terdon♦
Feb 1 at 18:22

1

@terdon, POSIX doesn't specify the path of the POSIX utilities. Again, there, the standard grep (that supports -F, -E, -e, -f as POSIX requires) is in /usr/xpg4/bin. The utilities in /bin are antiquated ones.

– Stéphane Chazelas
Feb 2 at 14:28

can also be written as grep -e foo -e bar | grep -v -e 'foo.*bar' -e 'bar.*foo'

– glenn jackman
Jan 30 at 13:40

Also, note from the grep man page: Direct invocation as either egrep or fgrep is deprecated -- prefer grep -E

– glenn jackman
Jan 30 at 13:41

That isn't in my OS @glennjackman

– Grump
Jan 30 at 15:14

@Grump really? What OS is that? Even POSIX mentions that grep should have -f and -e options although the older egrep and fgrep will continue to be supported for a while.

– terdon♦
Feb 1 at 18:22

@terdon, POSIX doesn't specify the path of the POSIX utilities. Again, there, the standard grep (that supports -F, -E, -e, -f as POSIX requires) is in /usr/xpg4/bin. The utilities in /bin are antiquated ones.

– Stéphane Chazelas
Feb 2 at 14:28

|
show 5 more comments

With grep implementations that support perl-like regular expressions (like pcregrep or GNU or ast-open grep -P), you can do it in one grep invocation with:

grep -P '^(?=.*pat1)(?!.*pat2)|^(?=.*pat2)(?!.*pat1)'

That is find the lines that match pat1 but not pat2, or pat2 but not pat1.

That's suboptimal for lines that contain both patterns as they would then be looked for twice. You could instead use more advanced perl operators like:

grep -P '^(?=.*pat1|())(?(1)(?=.*pat2)|(?!.*pat2))'

With sed, you could write it:

sed -ne '/pat1/{/pat2/!p;d;}' -e '/pat2/p'

edited Feb 1 at 14:08

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

Your first solution fails with grep: the -P option only supports a single pattern, at least on every system I have access to. +1 for your second solution, though.

– Chris
Jan 31 at 22:19

1

@Chris, you're right. That seems to be a limitation specific to GNU grep. pcregrep and ast-open grep don't have that problem. I've replaced the multiple -e with the alternation RE operator, so it should work with GNU grep as well now.

– Stéphane Chazelas
Jan 31 at 22:33

Yes, it works fine now.

– Chris
Jan 31 at 22:50

add a comment |

With grep implementations that support perl-like regular expressions (like pcregrep or GNU or ast-open grep -P), you can do it in one grep invocation with:

grep -P '^(?=.*pat1)(?!.*pat2)|^(?=.*pat2)(?!.*pat1)'

That is find the lines that match pat1 but not pat2, or pat2 but not pat1.

That's suboptimal for lines that contain both patterns as they would then be looked for twice. You could instead use more advanced perl operators like:

grep -P '^(?=.*pat1|())(?(1)(?=.*pat2)|(?!.*pat2))'

With sed, you could write it:

sed -ne '/pat1/{/pat2/!p;d;}' -e '/pat2/p'

edited Feb 1 at 14:08

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

Your first solution fails with grep: the -P option only supports a single pattern, at least on every system I have access to. +1 for your second solution, though.

– Chris
Jan 31 at 22:19

1

@Chris, you're right. That seems to be a limitation specific to GNU grep. pcregrep and ast-open grep don't have that problem. I've replaced the multiple -e with the alternation RE operator, so it should work with GNU grep as well now.

– Stéphane Chazelas
Jan 31 at 22:33

Yes, it works fine now.

– Chris
Jan 31 at 22:50

add a comment |

With grep implementations that support perl-like regular expressions (like pcregrep or GNU or ast-open grep -P), you can do it in one grep invocation with:

grep -P '^(?=.*pat1)(?!.*pat2)|^(?=.*pat2)(?!.*pat1)'

That is find the lines that match pat1 but not pat2, or pat2 but not pat1.

That's suboptimal for lines that contain both patterns as they would then be looked for twice. You could instead use more advanced perl operators like:

grep -P '^(?=.*pat1|())(?(1)(?=.*pat2)|(?!.*pat2))'

With sed, you could write it:

sed -ne '/pat1/{/pat2/!p;d;}' -e '/pat2/p'

edited Feb 1 at 14:08

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

With grep implementations that support perl-like regular expressions (like pcregrep or GNU or ast-open grep -P), you can do it in one grep invocation with:

grep -P '^(?=.*pat1)(?!.*pat2)|^(?=.*pat2)(?!.*pat1)'

That is find the lines that match pat1 but not pat2, or pat2 but not pat1.

That's suboptimal for lines that contain both patterns as they would then be looked for twice. You could instead use more advanced perl operators like:

grep -P '^(?=.*pat1|())(?(1)(?=.*pat2)|(?!.*pat2))'

With sed, you could write it:

sed -ne '/pat1/{/pat2/!p;d;}' -e '/pat2/p'

edited Feb 1 at 14:08

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

edited Feb 1 at 14:08

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

answered Jan 31 at 14:13

Stéphane Chazelas

313k57592948

Your first solution fails with grep: the -P option only supports a single pattern, at least on every system I have access to. +1 for your second solution, though.

– Chris
Jan 31 at 22:19

1

@Chris, you're right. That seems to be a limitation specific to GNU grep. pcregrep and ast-open grep don't have that problem. I've replaced the multiple -e with the alternation RE operator, so it should work with GNU grep as well now.

– Stéphane Chazelas
Jan 31 at 22:33

Yes, it works fine now.

– Chris
Jan 31 at 22:50

add a comment |

Your first solution fails with grep: the -P option only supports a single pattern, at least on every system I have access to. +1 for your second solution, though.

– Chris
Jan 31 at 22:19

1

@Chris, you're right. That seems to be a limitation specific to GNU grep. pcregrep and ast-open grep don't have that problem. I've replaced the multiple -e with the alternation RE operator, so it should work with GNU grep as well now.

– Stéphane Chazelas
Jan 31 at 22:33

Yes, it works fine now.

– Chris
Jan 31 at 22:50

Your first solution fails with grep: the -P option only supports a single pattern, at least on every system I have access to. +1 for your second solution, though.

– Chris
Jan 31 at 22:19

@Chris, you're right. That seems to be a limitation specific to GNU grep. pcregrep and ast-open grep don't have that problem. I've replaced the multiple -e with the alternation RE operator, so it should work with GNU grep as well now.

– Stéphane Chazelas
Jan 31 at 22:33

Yes, it works fine now.

– Chris
Jan 31 at 22:50

add a comment |

In Boolean terms, you're looking for A xor B, which can be written as

(A and not B)

(B and not A)

Given that your question doesn't mention that you are concerned with the order of the output so long as the matching lines are shown, the Boolean expansion of A xor B is pretty darn simple in grep:

$ cat << EOF > foo

> a b

> a

> b

> c a

> c b

> b a

> b c

> EOF

$ grep -w 'a' foo | grep -vw 'b'; grep -w 'b' foo | grep -vw 'a';

a

c a

b

c b

b c

edited Jan 30 at 23:42

answered Jan 30 at 20:58

Jim L.

1413

1

This works, but it will scramble the order of the file.

– Sparhawk
Jan 30 at 23:32

@Sparhawk True, although "scramble" is a harsh word. ;) it lists all the 'a' matches first, in order, then all the 'b' matches next, in order. The OP didn't express any interest in maintaining the order, just show the lines. FAWK, the next step could be sort | uniq.

– Jim L.
Jan 30 at 23:35

Fair call; I agree my language was inaccurate. I meant to imply that the original order would be changed.

– Sparhawk
Jan 30 at 23:43

1

@Sparhawk ... And I edited in your observation for full disclosure.

– Jim L.
Jan 30 at 23:44

add a comment |

In Boolean terms, you're looking for A xor B, which can be written as

(A and not B)

(B and not A)

Given that your question doesn't mention that you are concerned with the order of the output so long as the matching lines are shown, the Boolean expansion of A xor B is pretty darn simple in grep:

$ cat << EOF > foo

> a b

> a

> b

> c a

> c b

> b a

> b c

> EOF

$ grep -w 'a' foo | grep -vw 'b'; grep -w 'b' foo | grep -vw 'a';

a

c a

b

c b

b c

edited Jan 30 at 23:42

answered Jan 30 at 20:58

Jim L.

1413

1

This works, but it will scramble the order of the file.

– Sparhawk
Jan 30 at 23:32

@Sparhawk True, although "scramble" is a harsh word. ;) it lists all the 'a' matches first, in order, then all the 'b' matches next, in order. The OP didn't express any interest in maintaining the order, just show the lines. FAWK, the next step could be sort | uniq.

– Jim L.
Jan 30 at 23:35

Fair call; I agree my language was inaccurate. I meant to imply that the original order would be changed.

– Sparhawk
Jan 30 at 23:43

1

@Sparhawk ... And I edited in your observation for full disclosure.

– Jim L.
Jan 30 at 23:44

add a comment |

In Boolean terms, you're looking for A xor B, which can be written as

(A and not B)

(B and not A)

Given that your question doesn't mention that you are concerned with the order of the output so long as the matching lines are shown, the Boolean expansion of A xor B is pretty darn simple in grep:

$ cat << EOF > foo

> a b

> a

> b

> c a

> c b

> b a

> b c

> EOF

$ grep -w 'a' foo | grep -vw 'b'; grep -w 'b' foo | grep -vw 'a';

a

c a

b

c b

b c

edited Jan 30 at 23:42

answered Jan 30 at 20:58

Jim L.

1413

In Boolean terms, you're looking for A xor B, which can be written as

(A and not B)

(B and not A)

Given that your question doesn't mention that you are concerned with the order of the output so long as the matching lines are shown, the Boolean expansion of A xor B is pretty darn simple in grep:

$ cat << EOF > foo

> a b

> a

> b

> c a

> c b

> b a

> b c

> EOF

$ grep -w 'a' foo | grep -vw 'b'; grep -w 'b' foo | grep -vw 'a';

a

c a

b

c b

b c

edited Jan 30 at 23:42

answered Jan 30 at 20:58

Jim L.

1413

edited Jan 30 at 23:42

answered Jan 30 at 20:58

Jim L.

1413

answered Jan 30 at 20:58

Jim L.

1413

answered Jan 30 at 20:58

Jim L.

1413

1

This works, but it will scramble the order of the file.

– Sparhawk
Jan 30 at 23:32

@Sparhawk True, although "scramble" is a harsh word. ;) it lists all the 'a' matches first, in order, then all the 'b' matches next, in order. The OP didn't express any interest in maintaining the order, just show the lines. FAWK, the next step could be sort | uniq.

– Jim L.
Jan 30 at 23:35

Fair call; I agree my language was inaccurate. I meant to imply that the original order would be changed.

– Sparhawk
Jan 30 at 23:43

1

@Sparhawk ... And I edited in your observation for full disclosure.

– Jim L.
Jan 30 at 23:44

add a comment |

1

This works, but it will scramble the order of the file.

– Sparhawk
Jan 30 at 23:32

@Sparhawk True, although "scramble" is a harsh word. ;) it lists all the 'a' matches first, in order, then all the 'b' matches next, in order. The OP didn't express any interest in maintaining the order, just show the lines. FAWK, the next step could be sort | uniq.

– Jim L.
Jan 30 at 23:35

Fair call; I agree my language was inaccurate. I meant to imply that the original order would be changed.

– Sparhawk
Jan 30 at 23:43

1

@Sparhawk ... And I edited in your observation for full disclosure.

– Jim L.
Jan 30 at 23:44

This works, but it will scramble the order of the file.

– Sparhawk
Jan 30 at 23:32

@Sparhawk True, although "scramble" is a harsh word. ;) it lists all the 'a' matches first, in order, then all the 'b' matches next, in order. The OP didn't express any interest in maintaining the order, just show the lines. FAWK, the next step could be sort | uniq.

– Jim L.
Jan 30 at 23:35

Fair call; I agree my language was inaccurate. I meant to imply that the original order would be changed.

– Sparhawk
Jan 30 at 23:43

@Sparhawk ... And I edited in your observation for full disclosure.

– Jim L.
Jan 30 at 23:44

add a comment |

-1

For the following example:

# Patterns:

#    apple

#    pear



# Example line

line="a_apple_apple_pear_a"

This can be done purely with grep -E, uniq, and wc.

# Grep for regex pattern, sort as unique, and count the number of lines

result=$(grep -oE 'apple|pear' <<< $line | sort -u | wc -l)

If grep is compiled with Perl regular expressions then you can match on the last occurrence instead of needing to pipe to uniq:

# Grep for regex pattern and count the number of lines

result=$(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l)

Output the result:

# Only one of the words exists if the result is < 2

((result > 0)) &&

   if (($result < 2)); then

      echo Only one word matched

   else

      echo Both words matched

   fi

A one-liner:

(($(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l) == 1)) && echo Only one word matched

If you don't want to hard-code the pattern, assembling it with a variable set of elements can be automated with a function.

This can also be done natively in Bash as a function without pipes or additional processes but would be more involved and is probably outside the scope of your question.

edited Jan 31 at 7:13

answered Jan 31 at 4:16

Zhro

375414

(1) I was wondering when somebody was going to give an answer using Perl regular expressions. If you focused on that part of your post, and explained how it worked, this could be a good answer. (2) But I’m afraid the rest isn’t so good. The question says “show only lines containing either of the two words” (emphasis added). If the output is supposed to be lines, then it stands to reason that the input must also be multiple lines. But your approach works only when looking at only a single line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … For example, if the input contains the lines Big applen and pear-shapedn, then the output should contain both of those lines. Your solution would get a count of 2; the long version would report “Both words matched” (which is an answer to the wrong question) and the short version would say nothing at all. (3) A suggestion: using -o here is a really bad idea, because it hides the lines that contain the matches, so you can’t see when both words appear on the same line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … (4) Bottom line: your use of uniq / sort -u and the fancy Perl regular expression to match only the last occurrence on each line don’t really add up to a useful answer to this question. But, even if they did, it would still be a bad answer because you don’t explain how they contribute to answering the question. (See Stéphane Chazelas’s answer for an example of a good explanation.)

– G-Man
Feb 2 at 23:35

The OP says that they wanted to "show only lines containing either of the two words" which means that each line has to be evaluated on its own. I don't see why you feel that this doesn't answer the question. Please provide an example input that you feel would fail.

– Zhro
Feb 2 at 23:46

Oh, is that what you meant? “Read the input a line at a time and execute these two or three commands for every line.”? (1) It’s painfully unclear that that’s what you meant. (2) It’s painfully inefficient. Four answers before yours showed how to handle the entire file in a few commands (one, two or four), and you want to run 3 × n commands for n lines of input? Even if it works, it earns a down vote for unnecessarily expensive execution. (3) At the risk of splitting hairs, it still doesn’t do the job of showing the appropriate lines.

– G-Man
Feb 3 at 1:09

|
show 2 more comments

-1

For the following example:

# Patterns:

#    apple

#    pear



# Example line

line="a_apple_apple_pear_a"

This can be done purely with grep -E, uniq, and wc.

# Grep for regex pattern, sort as unique, and count the number of lines

result=$(grep -oE 'apple|pear' <<< $line | sort -u | wc -l)

If grep is compiled with Perl regular expressions then you can match on the last occurrence instead of needing to pipe to uniq:

# Grep for regex pattern and count the number of lines

result=$(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l)

Output the result:

# Only one of the words exists if the result is < 2

((result > 0)) &&

   if (($result < 2)); then

      echo Only one word matched

   else

      echo Both words matched

   fi

A one-liner:

(($(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l) == 1)) && echo Only one word matched

If you don't want to hard-code the pattern, assembling it with a variable set of elements can be automated with a function.

This can also be done natively in Bash as a function without pipes or additional processes but would be more involved and is probably outside the scope of your question.

edited Jan 31 at 7:13

answered Jan 31 at 4:16

Zhro

375414

(1) I was wondering when somebody was going to give an answer using Perl regular expressions. If you focused on that part of your post, and explained how it worked, this could be a good answer. (2) But I’m afraid the rest isn’t so good. The question says “show only lines containing either of the two words” (emphasis added). If the output is supposed to be lines, then it stands to reason that the input must also be multiple lines. But your approach works only when looking at only a single line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … For example, if the input contains the lines Big applen and pear-shapedn, then the output should contain both of those lines. Your solution would get a count of 2; the long version would report “Both words matched” (which is an answer to the wrong question) and the short version would say nothing at all. (3) A suggestion: using -o here is a really bad idea, because it hides the lines that contain the matches, so you can’t see when both words appear on the same line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … (4) Bottom line: your use of uniq / sort -u and the fancy Perl regular expression to match only the last occurrence on each line don’t really add up to a useful answer to this question. But, even if they did, it would still be a bad answer because you don’t explain how they contribute to answering the question. (See Stéphane Chazelas’s answer for an example of a good explanation.)

– G-Man
Feb 2 at 23:35

The OP says that they wanted to "show only lines containing either of the two words" which means that each line has to be evaluated on its own. I don't see why you feel that this doesn't answer the question. Please provide an example input that you feel would fail.

– Zhro
Feb 2 at 23:46

Oh, is that what you meant? “Read the input a line at a time and execute these two or three commands for every line.”? (1) It’s painfully unclear that that’s what you meant. (2) It’s painfully inefficient. Four answers before yours showed how to handle the entire file in a few commands (one, two or four), and you want to run 3 × n commands for n lines of input? Even if it works, it earns a down vote for unnecessarily expensive execution. (3) At the risk of splitting hairs, it still doesn’t do the job of showing the appropriate lines.

– G-Man
Feb 3 at 1:09

|
show 2 more comments

-1

For the following example:

# Patterns:

#    apple

#    pear



# Example line

line="a_apple_apple_pear_a"

This can be done purely with grep -E, uniq, and wc.

# Grep for regex pattern, sort as unique, and count the number of lines

result=$(grep -oE 'apple|pear' <<< $line | sort -u | wc -l)

If grep is compiled with Perl regular expressions then you can match on the last occurrence instead of needing to pipe to uniq:

# Grep for regex pattern and count the number of lines

result=$(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l)

Output the result:

# Only one of the words exists if the result is < 2

((result > 0)) &&

   if (($result < 2)); then

      echo Only one word matched

   else

      echo Both words matched

   fi

A one-liner:

(($(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l) == 1)) && echo Only one word matched

If you don't want to hard-code the pattern, assembling it with a variable set of elements can be automated with a function.

This can also be done natively in Bash as a function without pipes or additional processes but would be more involved and is probably outside the scope of your question.

edited Jan 31 at 7:13

answered Jan 31 at 4:16

Zhro

375414

For the following example:

# Patterns:

#    apple

#    pear



# Example line

line="a_apple_apple_pear_a"

This can be done purely with grep -E, uniq, and wc.

# Grep for regex pattern, sort as unique, and count the number of lines

result=$(grep -oE 'apple|pear' <<< $line | sort -u | wc -l)

If grep is compiled with Perl regular expressions then you can match on the last occurrence instead of needing to pipe to uniq:

# Grep for regex pattern and count the number of lines

result=$(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l)

Output the result:

# Only one of the words exists if the result is < 2

((result > 0)) &&

   if (($result < 2)); then

      echo Only one word matched

   else

      echo Both words matched

   fi

A one-liner:

(($(grep -oP '(apple(?!.*apple)|pear(?!.*pear))' <<< $line | wc -l) == 1)) && echo Only one word matched

If you don't want to hard-code the pattern, assembling it with a variable set of elements can be automated with a function.

This can also be done natively in Bash as a function without pipes or additional processes but would be more involved and is probably outside the scope of your question.

edited Jan 31 at 7:13

answered Jan 31 at 4:16

Zhro

375414

edited Jan 31 at 7:13

answered Jan 31 at 4:16

Zhro

375414

answered Jan 31 at 4:16

Zhro

375414

answered Jan 31 at 4:16

Zhro

375414

(1) I was wondering when somebody was going to give an answer using Perl regular expressions. If you focused on that part of your post, and explained how it worked, this could be a good answer. (2) But I’m afraid the rest isn’t so good. The question says “show only lines containing either of the two words” (emphasis added). If the output is supposed to be lines, then it stands to reason that the input must also be multiple lines. But your approach works only when looking at only a single line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … For example, if the input contains the lines Big applen and pear-shapedn, then the output should contain both of those lines. Your solution would get a count of 2; the long version would report “Both words matched” (which is an answer to the wrong question) and the short version would say nothing at all. (3) A suggestion: using -o here is a really bad idea, because it hides the lines that contain the matches, so you can’t see when both words appear on the same line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … (4) Bottom line: your use of uniq / sort -u and the fancy Perl regular expression to match only the last occurrence on each line don’t really add up to a useful answer to this question. But, even if they did, it would still be a bad answer because you don’t explain how they contribute to answering the question. (See Stéphane Chazelas’s answer for an example of a good explanation.)

– G-Man
Feb 2 at 23:35

The OP says that they wanted to "show only lines containing either of the two words" which means that each line has to be evaluated on its own. I don't see why you feel that this doesn't answer the question. Please provide an example input that you feel would fail.

– Zhro
Feb 2 at 23:46

Oh, is that what you meant? “Read the input a line at a time and execute these two or three commands for every line.”? (1) It’s painfully unclear that that’s what you meant. (2) It’s painfully inefficient. Four answers before yours showed how to handle the entire file in a few commands (one, two or four), and you want to run 3 × n commands for n lines of input? Even if it works, it earns a down vote for unnecessarily expensive execution. (3) At the risk of splitting hairs, it still doesn’t do the job of showing the appropriate lines.

– G-Man
Feb 3 at 1:09

|
show 2 more comments

(1) I was wondering when somebody was going to give an answer using Perl regular expressions. If you focused on that part of your post, and explained how it worked, this could be a good answer. (2) But I’m afraid the rest isn’t so good. The question says “show only lines containing either of the two words” (emphasis added). If the output is supposed to be lines, then it stands to reason that the input must also be multiple lines. But your approach works only when looking at only a single line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … For example, if the input contains the lines Big applen and pear-shapedn, then the output should contain both of those lines. Your solution would get a count of 2; the long version would report “Both words matched” (which is an answer to the wrong question) and the short version would say nothing at all. (3) A suggestion: using -o here is a really bad idea, because it hides the lines that contain the matches, so you can’t see when both words appear on the same line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … (4) Bottom line: your use of uniq / sort -u and the fancy Perl regular expression to match only the last occurrence on each line don’t really add up to a useful answer to this question. But, even if they did, it would still be a bad answer because you don’t explain how they contribute to answering the question. (See Stéphane Chazelas’s answer for an example of a good explanation.)

– G-Man
Feb 2 at 23:35

The OP says that they wanted to "show only lines containing either of the two words" which means that each line has to be evaluated on its own. I don't see why you feel that this doesn't answer the question. Please provide an example input that you feel would fail.

– Zhro
Feb 2 at 23:46

Oh, is that what you meant? “Read the input a line at a time and execute these two or three commands for every line.”? (1) It’s painfully unclear that that’s what you meant. (2) It’s painfully inefficient. Four answers before yours showed how to handle the entire file in a few commands (one, two or four), and you want to run 3 × n commands for n lines of input? Even if it works, it earns a down vote for unnecessarily expensive execution. (3) At the risk of splitting hairs, it still doesn’t do the job of showing the appropriate lines.

– G-Man
Feb 3 at 1:09

(1) I was wondering when somebody was going to give an answer using Perl regular expressions. If you focused on that part of your post, and explained how it worked, this could be a good answer. (2) But I’m afraid the rest isn’t so good. The question says “show only lines containing either of the two words” (emphasis added). If the output is supposed to be lines, then it stands to reason that the input must also be multiple lines. But your approach works only when looking at only a single line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … For example, if the input contains the lines Big applen and pear-shapedn, then the output should contain both of those lines. Your solution would get a count of 2; the long version would report “Both words matched” (which is an answer to the wrong question) and the short version would say nothing at all. (3) A suggestion: using -o here is a really bad idea, because it hides the lines that contain the matches, so you can’t see when both words appear on the same line. … (Cont’d)

– G-Man
Feb 2 at 23:35

(Cont’d) … (4) Bottom line: your use of uniq / sort -u and the fancy Perl regular expression to match only the last occurrence on each line don’t really add up to a useful answer to this question. But, even if they did, it would still be a bad answer because you don’t explain how they contribute to answering the question. (See Stéphane Chazelas’s answer for an example of a good explanation.)

– G-Man
Feb 2 at 23:35

The OP says that they wanted to "show only lines containing either of the two words" which means that each line has to be evaluated on its own. I don't see why you feel that this doesn't answer the question. Please provide an example input that you feel would fail.

– Zhro
Feb 2 at 23:46

Oh, is that what you meant? “Read the input a line at a time and execute these two or three commands for every line.”? (1) It’s painfully unclear that that’s what you meant. (2) It’s painfully inefficient. Four answers before yours showed how to handle the entire file in a few commands (one, two or four), and you want to run 3 × n commands for n lines of input? Even if it works, it earns a down vote for unnecessarily expensive execution. (3) At the risk of splitting hairs, it still doesn’t do the job of showing the appropriate lines.

– G-Man
Feb 3 at 1:09

|
show 2 more comments

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