Newlines in BSD sed vs gsed

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The sed, which comes with FreeBSD 11.2 p7, gives:

 $ seq 10 | sed 'N; l; D; p'

1$

2$

2$

3$

3$

4$

4$

5$

5$

6$

6$

7$

7$

8$

8$

9$

9$

10$

While gsed (GNU sed 4.7) gives for the same script:

$ seq 10 | gsed 'N; l; D; p'

1n2$

2n3$

3n4$

4n5$

5n6$

6n7$

7n8$

8n9$

9n10$

10

How can we explain this difference in behavior?

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

asked Mar 30 at 17:02

wolf-revo-cats

885935

add a comment |

The sed, which comes with FreeBSD 11.2 p7, gives:

 $ seq 10 | sed 'N; l; D; p'

1$

2$

2$

3$

3$

4$

4$

5$

5$

6$

6$

7$

7$

8$

8$

9$

9$

10$

While gsed (GNU sed 4.7) gives for the same script:

$ seq 10 | gsed 'N; l; D; p'

1n2$

2n3$

3n4$

4n5$

5n6$

6n7$

7n8$

8n9$

9n10$

10

How can we explain this difference in behavior?

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

asked Mar 30 at 17:02

wolf-revo-cats

885935

add a comment |

The sed, which comes with FreeBSD 11.2 p7, gives:

 $ seq 10 | sed 'N; l; D; p'

1$

2$

2$

3$

3$

4$

4$

5$

5$

6$

6$

7$

7$

8$

8$

9$

9$

10$

While gsed (GNU sed 4.7) gives for the same script:

$ seq 10 | gsed 'N; l; D; p'

1n2$

2n3$

3n4$

4n5$

5n6$

6n7$

7n8$

8n9$

9n10$

10

How can we explain this difference in behavior?

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

asked Mar 30 at 17:02

wolf-revo-cats

885935

The sed, which comes with FreeBSD 11.2 p7, gives:

 $ seq 10 | sed 'N; l; D; p'

1$

2$

2$

3$

3$

4$

4$

5$

5$

6$

6$

7$

7$

8$

8$

9$

9$

10$

While gsed (GNU sed 4.7) gives for the same script:

$ seq 10 | gsed 'N; l; D; p'

1n2$

2n3$

3n4$

4n5$

5n6$

6n7$

7n8$

8n9$

9n10$

10

How can we explain this difference in behavior?

sed gnu newlines bsd

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

asked Mar 30 at 17:02

wolf-revo-cats

885935

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

asked Mar 30 at 17:02

wolf-revo-cats

885935

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

edited Mar 30 at 17:18

Jeff Schaller♦

44.7k1163145

asked Mar 30 at 17:02

wolf-revo-cats

885935

asked Mar 30 at 17:02

wolf-revo-cats

885935

asked Mar 30 at 17:02

wolf-revo-cats

885935

add a comment |

1 Answer
1

active

oldest

votes

BSD sed, when using l to output characters in a visually unambiguous form, does not output newlines in a visually unambiguous form.

From sed(1) on OpenBSD:

 [2addr]l

         (The letter ell.)  Write the pattern space to the standard output

         in a visually unambiguous form.  This form is as follows:



               backslash          \

               alert              a

               backspace          b

               form-feed          f

               carriage-return    r

               tab                t

               vertical tab       v

(note lack of mentioning of newlines).

GNU sed, however, includes newlines in the set of characters to display unambiguously. It does this as an extension to the set of characters that the POSIX standard for sed mentions (which is the set that BSD sed uses). GNU sed behaves this way even if --posix is used on the command line.

GNU sed also outputs 10 twice, while BSD sed does not. Running GNU sed with POSIXLY_CORRECT set or with --posix will make it output 10 only once, like BSD sed does.

This is because GNU sed by default ignores the part of POSIX definition of the sed N command that says

If no next line of input is available, the N command verb shall branch to the end of the script and quit without starting a new cycle or copying the pattern space to standard output.

Note also that the p in your sed program never executes, as D starts a new cycle.

edited Mar 30 at 17:43

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

2

Another difference is 10 being displayed once with BSD sed, and this time GNU sed behaves like BSD sed with POSIXLY_CORRECT. That's why you generally want to use $!N instead of N when -n is not enabled.

– Stéphane Chazelas
Mar 30 at 17:29

@StéphaneChazelas Thanks. I did not notice that difference at first.

– Kusalananda♦
Mar 30 at 17:31

Note that ast-open's sed behaves like GNU sed wrt n displayed by l. I suspect the POSIX requirement is an oversight here (they say it's not applicable which doesn't make sense here, I suspect they say that because the pattern space normally doesn't contain newline by default but overlook the fact that it can be added by N, G, s...; if they wanted to require the original sed behaviour, they would have said something like newline shall be output literally or something like that)

– Stéphane Chazelas
Mar 30 at 17:34

add a comment |

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BSD sed, when using l to output characters in a visually unambiguous form, does not output newlines in a visually unambiguous form.

From sed(1) on OpenBSD:

 [2addr]l

         (The letter ell.)  Write the pattern space to the standard output

         in a visually unambiguous form.  This form is as follows:



               backslash          \

               alert              a

               backspace          b

               form-feed          f

               carriage-return    r

               tab                t

               vertical tab       v

(note lack of mentioning of newlines).

GNU sed also outputs 10 twice, while BSD sed does not. Running GNU sed with POSIXLY_CORRECT set or with --posix will make it output 10 only once, like BSD sed does.

This is because GNU sed by default ignores the part of POSIX definition of the sed N command that says

If no next line of input is available, the N command verb shall branch to the end of the script and quit without starting a new cycle or copying the pattern space to standard output.

Note also that the p in your sed program never executes, as D starts a new cycle.

edited Mar 30 at 17:43

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

2

Another difference is 10 being displayed once with BSD sed, and this time GNU sed behaves like BSD sed with POSIXLY_CORRECT. That's why you generally want to use $!N instead of N when -n is not enabled.

– Stéphane Chazelas
Mar 30 at 17:29

@StéphaneChazelas Thanks. I did not notice that difference at first.

– Kusalananda♦
Mar 30 at 17:31

Note that ast-open's sed behaves like GNU sed wrt n displayed by l. I suspect the POSIX requirement is an oversight here (they say it's not applicable which doesn't make sense here, I suspect they say that because the pattern space normally doesn't contain newline by default but overlook the fact that it can be added by N, G, s...; if they wanted to require the original sed behaviour, they would have said something like newline shall be output literally or something like that)

– Stéphane Chazelas
Mar 30 at 17:34

add a comment |

BSD sed, when using l to output characters in a visually unambiguous form, does not output newlines in a visually unambiguous form.

From sed(1) on OpenBSD:

 [2addr]l

         (The letter ell.)  Write the pattern space to the standard output

         in a visually unambiguous form.  This form is as follows:



               backslash          \

               alert              a

               backspace          b

               form-feed          f

               carriage-return    r

               tab                t

               vertical tab       v

(note lack of mentioning of newlines).

GNU sed also outputs 10 twice, while BSD sed does not. Running GNU sed with POSIXLY_CORRECT set or with --posix will make it output 10 only once, like BSD sed does.

This is because GNU sed by default ignores the part of POSIX definition of the sed N command that says

If no next line of input is available, the N command verb shall branch to the end of the script and quit without starting a new cycle or copying the pattern space to standard output.

Note also that the p in your sed program never executes, as D starts a new cycle.

edited Mar 30 at 17:43

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

2

Another difference is 10 being displayed once with BSD sed, and this time GNU sed behaves like BSD sed with POSIXLY_CORRECT. That's why you generally want to use $!N instead of N when -n is not enabled.

– Stéphane Chazelas
Mar 30 at 17:29

@StéphaneChazelas Thanks. I did not notice that difference at first.

– Kusalananda♦
Mar 30 at 17:31

Note that ast-open's sed behaves like GNU sed wrt n displayed by l. I suspect the POSIX requirement is an oversight here (they say it's not applicable which doesn't make sense here, I suspect they say that because the pattern space normally doesn't contain newline by default but overlook the fact that it can be added by N, G, s...; if they wanted to require the original sed behaviour, they would have said something like newline shall be output literally or something like that)

– Stéphane Chazelas
Mar 30 at 17:34

add a comment |

BSD sed, when using l to output characters in a visually unambiguous form, does not output newlines in a visually unambiguous form.

From sed(1) on OpenBSD:

 [2addr]l

         (The letter ell.)  Write the pattern space to the standard output

         in a visually unambiguous form.  This form is as follows:



               backslash          \

               alert              a

               backspace          b

               form-feed          f

               carriage-return    r

               tab                t

               vertical tab       v

(note lack of mentioning of newlines).

GNU sed also outputs 10 twice, while BSD sed does not. Running GNU sed with POSIXLY_CORRECT set or with --posix will make it output 10 only once, like BSD sed does.

This is because GNU sed by default ignores the part of POSIX definition of the sed N command that says

If no next line of input is available, the N command verb shall branch to the end of the script and quit without starting a new cycle or copying the pattern space to standard output.

Note also that the p in your sed program never executes, as D starts a new cycle.

edited Mar 30 at 17:43

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

BSD sed, when using l to output characters in a visually unambiguous form, does not output newlines in a visually unambiguous form.

From sed(1) on OpenBSD:

 [2addr]l

         (The letter ell.)  Write the pattern space to the standard output

         in a visually unambiguous form.  This form is as follows:



               backslash          \

               alert              a

               backspace          b

               form-feed          f

               carriage-return    r

               tab                t

               vertical tab       v

(note lack of mentioning of newlines).

GNU sed also outputs 10 twice, while BSD sed does not. Running GNU sed with POSIXLY_CORRECT set or with --posix will make it output 10 only once, like BSD sed does.

This is because GNU sed by default ignores the part of POSIX definition of the sed N command that says

If no next line of input is available, the N command verb shall branch to the end of the script and quit without starting a new cycle or copying the pattern space to standard output.

Note also that the p in your sed program never executes, as D starts a new cycle.

edited Mar 30 at 17:43

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

edited Mar 30 at 17:43

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

answered Mar 30 at 17:15

Kusalananda♦

140k17261435

2

Another difference is 10 being displayed once with BSD sed, and this time GNU sed behaves like BSD sed with POSIXLY_CORRECT. That's why you generally want to use $!N instead of N when -n is not enabled.

– Stéphane Chazelas
Mar 30 at 17:29

@StéphaneChazelas Thanks. I did not notice that difference at first.

– Kusalananda♦
Mar 30 at 17:31

Note that ast-open's sed behaves like GNU sed wrt n displayed by l. I suspect the POSIX requirement is an oversight here (they say it's not applicable which doesn't make sense here, I suspect they say that because the pattern space normally doesn't contain newline by default but overlook the fact that it can be added by N, G, s...; if they wanted to require the original sed behaviour, they would have said something like newline shall be output literally or something like that)

– Stéphane Chazelas
Mar 30 at 17:34

add a comment |

2

Another difference is 10 being displayed once with BSD sed, and this time GNU sed behaves like BSD sed with POSIXLY_CORRECT. That's why you generally want to use $!N instead of N when -n is not enabled.

– Stéphane Chazelas
Mar 30 at 17:29

@StéphaneChazelas Thanks. I did not notice that difference at first.

– Kusalananda♦
Mar 30 at 17:31

Note that ast-open's sed behaves like GNU sed wrt n displayed by l. I suspect the POSIX requirement is an oversight here (they say it's not applicable which doesn't make sense here, I suspect they say that because the pattern space normally doesn't contain newline by default but overlook the fact that it can be added by N, G, s...; if they wanted to require the original sed behaviour, they would have said something like newline shall be output literally or something like that)

– Stéphane Chazelas
Mar 30 at 17:34

Another difference is 10 being displayed once with BSD sed, and this time GNU sed behaves like BSD sed with POSIXLY_CORRECT. That's why you generally want to use $!N instead of N when -n is not enabled.

– Stéphane Chazelas
Mar 30 at 17:29

@StéphaneChazelas Thanks. I did not notice that difference at first.

– Kusalananda♦
Mar 30 at 17:31

Note that ast-open's sed behaves like GNU sed wrt n displayed by l. I suspect the POSIX requirement is an oversight here (they say it's not applicable which doesn't make sense here, I suspect they say that because the pattern space normally doesn't contain newline by default but overlook the fact that it can be added by N, G, s...; if they wanted to require the original sed behaviour, they would have said something like newline shall be output literally or something like that)

– Stéphane Chazelas
Mar 30 at 17:34

add a comment |

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