delete lines matching pattern if it is repeated

Say I have a config file:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[extra]
[footer]
[tail]
print = true
[end]

I want to print the headers ([text]) only if there are options underneath. So the output should be:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[tail]
print = true

edited Feb 20 at 4:33

asked Feb 20 at 3:47

DarkHeart

3,52632341

Why must it be sed, rather than awk or perl?

– Ed Grimm
Feb 20 at 4:26

@EdGrimm - It doesn't really. I just wanted some simple one-liner. I've removed sed from the question.

– DarkHeart
Feb 20 at 4:35

add a comment |

Say I have a config file:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[extra]
[footer]
[tail]
print = true
[end]

I want to print the headers ([text]) only if there are options underneath. So the output should be:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[tail]
print = true

edited Feb 20 at 4:33

asked Feb 20 at 3:47

DarkHeart

3,52632341

Why must it be sed, rather than awk or perl?

– Ed Grimm
Feb 20 at 4:26

@EdGrimm - It doesn't really. I just wanted some simple one-liner. I've removed sed from the question.

– DarkHeart
Feb 20 at 4:35

add a comment |

Say I have a config file:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[extra]
[footer]
[tail]
print = true
[end]

I want to print the headers ([text]) only if there are options underneath. So the output should be:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[tail]
print = true

edited Feb 20 at 4:33

asked Feb 20 at 3:47

DarkHeart

3,52632341

Say I have a config file:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[extra]
[footer]
[tail]
print = true
[end]

I want to print the headers ([text]) only if there are options underneath. So the output should be:

[main]
foo = bar
[option]
opt1 = opt2
opt3 = opt4
[tail]
print = true

text-processing awk sed perl

edited Feb 20 at 4:33

asked Feb 20 at 3:47

DarkHeart

3,52632341

edited Feb 20 at 4:33

asked Feb 20 at 3:47

DarkHeart

3,52632341

edited Feb 20 at 4:33

asked Feb 20 at 3:47

DarkHeart

3,52632341

asked Feb 20 at 3:47

DarkHeart

3,52632341

asked Feb 20 at 3:47

DarkHeart

3,52632341

Why must it be sed, rather than awk or perl?

– Ed Grimm
Feb 20 at 4:26

@EdGrimm - It doesn't really. I just wanted some simple one-liner. I've removed sed from the question.

– DarkHeart
Feb 20 at 4:35

add a comment |

Why must it be sed, rather than awk or perl?

– Ed Grimm
Feb 20 at 4:26

@EdGrimm - It doesn't really. I just wanted some simple one-liner. I've removed sed from the question.

– DarkHeart
Feb 20 at 4:35

Why must it be sed, rather than awk or perl?

– Ed Grimm
Feb 20 at 4:26

@EdGrimm - It doesn't really. I just wanted some simple one-liner. I've removed sed from the question.

– DarkHeart
Feb 20 at 4:35

add a comment |

1 Answer
1

active

oldest

votes

Normally, I'd write this in multiple lines for legibility, but since you asked for a one-liner:

perl -ne '$head = $_ and next if /^[/; $head and print $head and undef $head; print'

answered Feb 20 at 4:41

Ed Grimm

4988

1

I recall seeing awk that could do it in fewer characters, but I don't use awk due to the overhead from always splitting lines into words. For most uses, that difference in time is not relevant, but I've spent too much of my career writing log parsing scripts that consume multi-gigabyte logs, so I haven't exercised my awk muscles.

– Ed Grimm
Feb 20 at 4:44

2

Thanks - I can convert that to awk as awk '/^[/head=$0; nextheadprint head;head=""1'

– DarkHeart
Feb 20 at 4:56

add a comment |

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1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

Normally, I'd write this in multiple lines for legibility, but since you asked for a one-liner:

perl -ne '$head = $_ and next if /^[/; $head and print $head and undef $head; print'

answered Feb 20 at 4:41

Ed Grimm

4988

1

I recall seeing awk that could do it in fewer characters, but I don't use awk due to the overhead from always splitting lines into words. For most uses, that difference in time is not relevant, but I've spent too much of my career writing log parsing scripts that consume multi-gigabyte logs, so I haven't exercised my awk muscles.

– Ed Grimm
Feb 20 at 4:44

2

Thanks - I can convert that to awk as awk '/^[/head=$0; nextheadprint head;head=""1'

– DarkHeart
Feb 20 at 4:56

add a comment |

Normally, I'd write this in multiple lines for legibility, but since you asked for a one-liner:

perl -ne '$head = $_ and next if /^[/; $head and print $head and undef $head; print'

answered Feb 20 at 4:41

Ed Grimm

4988

1

I recall seeing awk that could do it in fewer characters, but I don't use awk due to the overhead from always splitting lines into words. For most uses, that difference in time is not relevant, but I've spent too much of my career writing log parsing scripts that consume multi-gigabyte logs, so I haven't exercised my awk muscles.

– Ed Grimm
Feb 20 at 4:44

2

Thanks - I can convert that to awk as awk '/^[/head=$0; nextheadprint head;head=""1'

– DarkHeart
Feb 20 at 4:56

add a comment |

Normally, I'd write this in multiple lines for legibility, but since you asked for a one-liner:

perl -ne '$head = $_ and next if /^[/; $head and print $head and undef $head; print'

answered Feb 20 at 4:41

Ed Grimm

4988

Normally, I'd write this in multiple lines for legibility, but since you asked for a one-liner:

perl -ne '$head = $_ and next if /^[/; $head and print $head and undef $head; print'

answered Feb 20 at 4:41

Ed Grimm

4988

answered Feb 20 at 4:41

Ed Grimm

4988

answered Feb 20 at 4:41

Ed Grimm

4988

answered Feb 20 at 4:41

Ed Grimm

4988

1

I recall seeing awk that could do it in fewer characters, but I don't use awk due to the overhead from always splitting lines into words. For most uses, that difference in time is not relevant, but I've spent too much of my career writing log parsing scripts that consume multi-gigabyte logs, so I haven't exercised my awk muscles.

– Ed Grimm
Feb 20 at 4:44

2

Thanks - I can convert that to awk as awk '/^[/head=$0; nextheadprint head;head=""1'

– DarkHeart
Feb 20 at 4:56

add a comment |

1

I recall seeing awk that could do it in fewer characters, but I don't use awk due to the overhead from always splitting lines into words. For most uses, that difference in time is not relevant, but I've spent too much of my career writing log parsing scripts that consume multi-gigabyte logs, so I haven't exercised my awk muscles.

– Ed Grimm
Feb 20 at 4:44

2

Thanks - I can convert that to awk as awk '/^[/head=$0; nextheadprint head;head=""1'

– DarkHeart
Feb 20 at 4:56

I recall seeing awk that could do it in fewer characters, but I don't use awk due to the overhead from always splitting lines into words. For most uses, that difference in time is not relevant, but I've spent too much of my career writing log parsing scripts that consume multi-gigabyte logs, so I haven't exercised my awk muscles.

– Ed Grimm
Feb 20 at 4:44

Thanks - I can convert that to awk as awk '/^[/head=$0; nextheadprint head;head=""1'

– DarkHeart
Feb 20 at 4:56

add a comment |

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