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How to get the n-th line after a grepped one?
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Consider the following text file
one 1
two 2
three 3
four 4
five 5
six 6
seven 7
eight 8
I would like to access to the second line after the one which matched four
. This would be the line
six 6
The resulting line (so the one above) would then be piped for further processing (say, a | cut -d' ' -f2
).
Is there a way to do this in bash and other typical utilities? (otherwise I will script it in Python)
linux command-line bash grep
add a comment |
Consider the following text file
one 1
two 2
three 3
four 4
five 5
six 6
seven 7
eight 8
I would like to access to the second line after the one which matched four
. This would be the line
six 6
The resulting line (so the one above) would then be piped for further processing (say, a | cut -d' ' -f2
).
Is there a way to do this in bash and other typical utilities? (otherwise I will script it in Python)
linux command-line bash grep
1
Will there always only be one occurrence of what you are trying to match? Will it always be two lines after?
– Nasir Riley
4 hours ago
Use awk? But if you're more familiar with Python that would be quicker.
– MZB
3 hours ago
add a comment |
Consider the following text file
one 1
two 2
three 3
four 4
five 5
six 6
seven 7
eight 8
I would like to access to the second line after the one which matched four
. This would be the line
six 6
The resulting line (so the one above) would then be piped for further processing (say, a | cut -d' ' -f2
).
Is there a way to do this in bash and other typical utilities? (otherwise I will script it in Python)
linux command-line bash grep
Consider the following text file
one 1
two 2
three 3
four 4
five 5
six 6
seven 7
eight 8
I would like to access to the second line after the one which matched four
. This would be the line
six 6
The resulting line (so the one above) would then be piped for further processing (say, a | cut -d' ' -f2
).
Is there a way to do this in bash and other typical utilities? (otherwise I will script it in Python)
linux command-line bash grep
linux command-line bash grep
asked 5 hours ago
WoJWoJ
82232238
82232238
1
Will there always only be one occurrence of what you are trying to match? Will it always be two lines after?
– Nasir Riley
4 hours ago
Use awk? But if you're more familiar with Python that would be quicker.
– MZB
3 hours ago
add a comment |
1
Will there always only be one occurrence of what you are trying to match? Will it always be two lines after?
– Nasir Riley
4 hours ago
Use awk? But if you're more familiar with Python that would be quicker.
– MZB
3 hours ago
1
1
Will there always only be one occurrence of what you are trying to match? Will it always be two lines after?
– Nasir Riley
4 hours ago
Will there always only be one occurrence of what you are trying to match? Will it always be two lines after?
– Nasir Riley
4 hours ago
Use awk? But if you're more familiar with Python that would be quicker.
– MZB
3 hours ago
Use awk? But if you're more familiar with Python that would be quicker.
– MZB
3 hours ago
add a comment |
4 Answers
4
active
oldest
votes
There is nothing wrong with the previous two answers, but I thought I would make you aware that finding the third line after a pattern can be done in a single sed
call:
sed -n "/four/ { n; n; p }" SourceData.txt
Because a single program does the work, this is more efficient than running multiple filters. The above command outputs the third line after every instance of "four", except where this occurs again in one of the two lines following a match (the other solutions don't handle this case in the expected manner either); also, no output is generated if the pattern is in the last or second-last line of the file, which may or may not be what you want.
To match the first instance only:
sed -n "/four/ { n; n; p; q }" SourceData.txt
I add this solution because it is worth getting to know sed
and, despite its rather off-putting syntax (regular expressions are bad enough!), it can often be extremely useful. This tutorial is a good introduction.
"the other solutions don't handle this case in the expected manner either" – No longer true. :)
– Kamil Maciorowski
1 hour ago
add a comment |
You can use this expression (input.txt
):
grep "four" -A 2 input.txt | tail -n 1
Output is:
six 6
The grep
option "-A 2" states that two lines after the matched line are outputted.
And the tail
option "-n 1" states that only the last 1
lines of this result are returned.
add a comment |
For multiple occurences, and assumming that no lines start with --
:
( grep -A 2 pattern data.txt; echo '--' ) | grep -E -B1 '^--' | grep -Ev '^--'
In slo-mo:
( grep -A 2 pattern data.txt; echo '--' )
prints the pattern and the next two lines, and inserts a--
line between the groups.echo '--'
makes sure that the last group is also followed by--
.
grep -E -B1 '^--'
print the separators and the lines just before (whoch are the ones we are looking for)
grep -Ev '^--'
drops the separators, leaving only the lines we are looking for.
if you use the-A
,-B
or-C
option thengrep
automatically use--
to separate matches, no need to print it yourself
– phuclv
2 hours ago
add a comment |
This solution prints the current line iff there was a match two lines ago. It is slightly different from other answers (so far) because it won't miss another match even if it occurs soon after the previous match.
awk -v delay=2 '{for (i=delay; i>=0; i--) t[i]=t[i-1]}; /four/ {t[0]="m"}; {if (t[delay]) print}'
Whenever there's a match, the information is stored in t[0]
. With each line the t
array is shifted (including shifting t[-1]
to t[0]
to reset the value of t[0]
). The line is printed iff the array indicates there was a match two lines ago.
You can easily set a different delay (e.g. delay=7
) or use another pattern (e.g. /sda[[:digit:]]/
)
add a comment |
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4 Answers
4
active
oldest
votes
4 Answers
4
active
oldest
votes
active
oldest
votes
active
oldest
votes
There is nothing wrong with the previous two answers, but I thought I would make you aware that finding the third line after a pattern can be done in a single sed
call:
sed -n "/four/ { n; n; p }" SourceData.txt
Because a single program does the work, this is more efficient than running multiple filters. The above command outputs the third line after every instance of "four", except where this occurs again in one of the two lines following a match (the other solutions don't handle this case in the expected manner either); also, no output is generated if the pattern is in the last or second-last line of the file, which may or may not be what you want.
To match the first instance only:
sed -n "/four/ { n; n; p; q }" SourceData.txt
I add this solution because it is worth getting to know sed
and, despite its rather off-putting syntax (regular expressions are bad enough!), it can often be extremely useful. This tutorial is a good introduction.
"the other solutions don't handle this case in the expected manner either" – No longer true. :)
– Kamil Maciorowski
1 hour ago
add a comment |
There is nothing wrong with the previous two answers, but I thought I would make you aware that finding the third line after a pattern can be done in a single sed
call:
sed -n "/four/ { n; n; p }" SourceData.txt
Because a single program does the work, this is more efficient than running multiple filters. The above command outputs the third line after every instance of "four", except where this occurs again in one of the two lines following a match (the other solutions don't handle this case in the expected manner either); also, no output is generated if the pattern is in the last or second-last line of the file, which may or may not be what you want.
To match the first instance only:
sed -n "/four/ { n; n; p; q }" SourceData.txt
I add this solution because it is worth getting to know sed
and, despite its rather off-putting syntax (regular expressions are bad enough!), it can often be extremely useful. This tutorial is a good introduction.
"the other solutions don't handle this case in the expected manner either" – No longer true. :)
– Kamil Maciorowski
1 hour ago
add a comment |
There is nothing wrong with the previous two answers, but I thought I would make you aware that finding the third line after a pattern can be done in a single sed
call:
sed -n "/four/ { n; n; p }" SourceData.txt
Because a single program does the work, this is more efficient than running multiple filters. The above command outputs the third line after every instance of "four", except where this occurs again in one of the two lines following a match (the other solutions don't handle this case in the expected manner either); also, no output is generated if the pattern is in the last or second-last line of the file, which may or may not be what you want.
To match the first instance only:
sed -n "/four/ { n; n; p; q }" SourceData.txt
I add this solution because it is worth getting to know sed
and, despite its rather off-putting syntax (regular expressions are bad enough!), it can often be extremely useful. This tutorial is a good introduction.
There is nothing wrong with the previous two answers, but I thought I would make you aware that finding the third line after a pattern can be done in a single sed
call:
sed -n "/four/ { n; n; p }" SourceData.txt
Because a single program does the work, this is more efficient than running multiple filters. The above command outputs the third line after every instance of "four", except where this occurs again in one of the two lines following a match (the other solutions don't handle this case in the expected manner either); also, no output is generated if the pattern is in the last or second-last line of the file, which may or may not be what you want.
To match the first instance only:
sed -n "/four/ { n; n; p; q }" SourceData.txt
I add this solution because it is worth getting to know sed
and, despite its rather off-putting syntax (regular expressions are bad enough!), it can often be extremely useful. This tutorial is a good introduction.
answered 3 hours ago
AFHAFH
14.4k31938
14.4k31938
"the other solutions don't handle this case in the expected manner either" – No longer true. :)
– Kamil Maciorowski
1 hour ago
add a comment |
"the other solutions don't handle this case in the expected manner either" – No longer true. :)
– Kamil Maciorowski
1 hour ago
"the other solutions don't handle this case in the expected manner either" – No longer true. :)
– Kamil Maciorowski
1 hour ago
"the other solutions don't handle this case in the expected manner either" – No longer true. :)
– Kamil Maciorowski
1 hour ago
add a comment |
You can use this expression (input.txt
):
grep "four" -A 2 input.txt | tail -n 1
Output is:
six 6
The grep
option "-A 2" states that two lines after the matched line are outputted.
And the tail
option "-n 1" states that only the last 1
lines of this result are returned.
add a comment |
You can use this expression (input.txt
):
grep "four" -A 2 input.txt | tail -n 1
Output is:
six 6
The grep
option "-A 2" states that two lines after the matched line are outputted.
And the tail
option "-n 1" states that only the last 1
lines of this result are returned.
add a comment |
You can use this expression (input.txt
):
grep "four" -A 2 input.txt | tail -n 1
Output is:
six 6
The grep
option "-A 2" states that two lines after the matched line are outputted.
And the tail
option "-n 1" states that only the last 1
lines of this result are returned.
You can use this expression (input.txt
):
grep "four" -A 2 input.txt | tail -n 1
Output is:
six 6
The grep
option "-A 2" states that two lines after the matched line are outputted.
And the tail
option "-n 1" states that only the last 1
lines of this result are returned.
answered 5 hours ago
zx485zx485
1,0311913
1,0311913
add a comment |
add a comment |
For multiple occurences, and assumming that no lines start with --
:
( grep -A 2 pattern data.txt; echo '--' ) | grep -E -B1 '^--' | grep -Ev '^--'
In slo-mo:
( grep -A 2 pattern data.txt; echo '--' )
prints the pattern and the next two lines, and inserts a--
line between the groups.echo '--'
makes sure that the last group is also followed by--
.
grep -E -B1 '^--'
print the separators and the lines just before (whoch are the ones we are looking for)
grep -Ev '^--'
drops the separators, leaving only the lines we are looking for.
if you use the-A
,-B
or-C
option thengrep
automatically use--
to separate matches, no need to print it yourself
– phuclv
2 hours ago
add a comment |
For multiple occurences, and assumming that no lines start with --
:
( grep -A 2 pattern data.txt; echo '--' ) | grep -E -B1 '^--' | grep -Ev '^--'
In slo-mo:
( grep -A 2 pattern data.txt; echo '--' )
prints the pattern and the next two lines, and inserts a--
line between the groups.echo '--'
makes sure that the last group is also followed by--
.
grep -E -B1 '^--'
print the separators and the lines just before (whoch are the ones we are looking for)
grep -Ev '^--'
drops the separators, leaving only the lines we are looking for.
if you use the-A
,-B
or-C
option thengrep
automatically use--
to separate matches, no need to print it yourself
– phuclv
2 hours ago
add a comment |
For multiple occurences, and assumming that no lines start with --
:
( grep -A 2 pattern data.txt; echo '--' ) | grep -E -B1 '^--' | grep -Ev '^--'
In slo-mo:
( grep -A 2 pattern data.txt; echo '--' )
prints the pattern and the next two lines, and inserts a--
line between the groups.echo '--'
makes sure that the last group is also followed by--
.
grep -E -B1 '^--'
print the separators and the lines just before (whoch are the ones we are looking for)
grep -Ev '^--'
drops the separators, leaving only the lines we are looking for.
For multiple occurences, and assumming that no lines start with --
:
( grep -A 2 pattern data.txt; echo '--' ) | grep -E -B1 '^--' | grep -Ev '^--'
In slo-mo:
( grep -A 2 pattern data.txt; echo '--' )
prints the pattern and the next two lines, and inserts a--
line between the groups.echo '--'
makes sure that the last group is also followed by--
.
grep -E -B1 '^--'
print the separators and the lines just before (whoch are the ones we are looking for)
grep -Ev '^--'
drops the separators, leaving only the lines we are looking for.
answered 4 hours ago
xenoidxenoid
3,8193719
3,8193719
if you use the-A
,-B
or-C
option thengrep
automatically use--
to separate matches, no need to print it yourself
– phuclv
2 hours ago
add a comment |
if you use the-A
,-B
or-C
option thengrep
automatically use--
to separate matches, no need to print it yourself
– phuclv
2 hours ago
if you use the
-A
, -B
or -C
option then grep
automatically use --
to separate matches, no need to print it yourself– phuclv
2 hours ago
if you use the
-A
, -B
or -C
option then grep
automatically use --
to separate matches, no need to print it yourself– phuclv
2 hours ago
add a comment |
This solution prints the current line iff there was a match two lines ago. It is slightly different from other answers (so far) because it won't miss another match even if it occurs soon after the previous match.
awk -v delay=2 '{for (i=delay; i>=0; i--) t[i]=t[i-1]}; /four/ {t[0]="m"}; {if (t[delay]) print}'
Whenever there's a match, the information is stored in t[0]
. With each line the t
array is shifted (including shifting t[-1]
to t[0]
to reset the value of t[0]
). The line is printed iff the array indicates there was a match two lines ago.
You can easily set a different delay (e.g. delay=7
) or use another pattern (e.g. /sda[[:digit:]]/
)
add a comment |
This solution prints the current line iff there was a match two lines ago. It is slightly different from other answers (so far) because it won't miss another match even if it occurs soon after the previous match.
awk -v delay=2 '{for (i=delay; i>=0; i--) t[i]=t[i-1]}; /four/ {t[0]="m"}; {if (t[delay]) print}'
Whenever there's a match, the information is stored in t[0]
. With each line the t
array is shifted (including shifting t[-1]
to t[0]
to reset the value of t[0]
). The line is printed iff the array indicates there was a match two lines ago.
You can easily set a different delay (e.g. delay=7
) or use another pattern (e.g. /sda[[:digit:]]/
)
add a comment |
This solution prints the current line iff there was a match two lines ago. It is slightly different from other answers (so far) because it won't miss another match even if it occurs soon after the previous match.
awk -v delay=2 '{for (i=delay; i>=0; i--) t[i]=t[i-1]}; /four/ {t[0]="m"}; {if (t[delay]) print}'
Whenever there's a match, the information is stored in t[0]
. With each line the t
array is shifted (including shifting t[-1]
to t[0]
to reset the value of t[0]
). The line is printed iff the array indicates there was a match two lines ago.
You can easily set a different delay (e.g. delay=7
) or use another pattern (e.g. /sda[[:digit:]]/
)
This solution prints the current line iff there was a match two lines ago. It is slightly different from other answers (so far) because it won't miss another match even if it occurs soon after the previous match.
awk -v delay=2 '{for (i=delay; i>=0; i--) t[i]=t[i-1]}; /four/ {t[0]="m"}; {if (t[delay]) print}'
Whenever there's a match, the information is stored in t[0]
. With each line the t
array is shifted (including shifting t[-1]
to t[0]
to reset the value of t[0]
). The line is printed iff the array indicates there was a match two lines ago.
You can easily set a different delay (e.g. delay=7
) or use another pattern (e.g. /sda[[:digit:]]/
)
answered 1 hour ago
Kamil MaciorowskiKamil Maciorowski
28.3k156186
28.3k156186
add a comment |
add a comment |
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1
Will there always only be one occurrence of what you are trying to match? Will it always be two lines after?
– Nasir Riley
4 hours ago
Use awk? But if you're more familiar with Python that would be quicker.
– MZB
3 hours ago