This question already has answers here:
How to get the part of a file after the first line that matches a regular expression
(12 answers)
Closed 7 years ago.
I have a file that contains a list of URLs. It looks like below:
file1:
http://www.google.com
http://www.bing.com
http://www.yahoo.com
http://www.baidu.com
http://www.yandex.com
....
I want to get all the records after: http://www.yahoo.com, results looks like below:
file2:
http://www.baidu.com
http://www.yandex.com
....
I know that I could use grep to find the line number of where yahoo.com lies using
grep -n 'http://www.yahoo.com' file1
3 http://www.yahoo.com
But I don't know how to get the file after line number 3. Also, I know there is a flag in grep -A print the lines after your match. However, you need to specify how many lines you want after the match. I am wondering is there something to get around that issue. Like:
Pseudocode:
grep -n 'http://www.yahoo.com' -A all file1 > file2
I know we could use the line number I got and wc -l to get the number of lines after yahoo.com, however... it feels pretty lame.
AWK
If you don't mind using AWK:
awk '/yahoo/{y=1;next}y' data.txt
This script has two parts:
/yahoo/ { y = 1; next }
y
The first part states that if we encounter a line with yahoo, we set the variable y=1, and then skip that line (the next command will jump to the next line, thus skip any further processing on the current line). Without the next command, the line yahoo will be printed.
The second part is a short hand for:
y != 0 { print }
Which means, for each line, if variable y is non-zero, we print that line. In AWK, if you refer to a variable, that variable will be created and is either zero or empty string, depending on context. Before encounter yahoo, variable y is 0, so the script does not print anything. After encounter yahoo, y is 1, so every line after that will be printed.
Sed
Or, using sed, the following will delete everything up to and including the line with yahoo:
sed '1,/yahoo/d' data.txt
This is much easier done with sed than grep. sed can apply any of its one-letter commands to an inclusive range of lines; the general syntax for this is
START , STOP COMMAND
except without any spaces. START and STOP can each be a number (meaning "line number N", starting from 1); a dollar sign (meaning "the end of the file"), or a regexp enclosed in slashes, meaning "the first line that matches this regexp". (The exact rules are slightly more complicated; the GNU sed manual has more detail.)
So, you can do what you want like so:
sed -n -e '/http:\/\/www\.yahoo\.com/,$p' file1 > file2
The -n means "don't print anything unless specifically told to", and the -e directive means "from the first appearance of a line that matches the regexp /http:\/\/www\.yahoo\.com/ to the end of the file, print."
This will include the line with http://www.yahoo.com/ on it in the output. If you want everything after that point but not that line itself, the easiest way to do that is to invert the operation:
sed -e '1,/http:\/\/www\.yahoo\.com/d' file1 > file2
which means "for line 1 through the first line matching the regexp /http:\/\/www\.yahoo\.com/, delete the line" (and then, implicitly, print everything else; note that -n is not used this time).
awk '/yahoo/ ? c++ : c' file1
Or golfed
awk '/yahoo/?c++:c' file1
Result
http://www.baidu.com
http://www.yandex.com
This is most easily done in Perl:
perl -ne 'print unless 1 .. m(http://www\.yahoo\.com)' file
In other words, print all lines that aren’t between line 1 and the first occurrence of that pattern.
Using this script:
# Get index of the "yahoo" word
index=`grep -n "yahoo" filepath | cut -d':' -f1`
# Get the total number of lines in the file
totallines=`wc -l filepath | cut -d' ' -f1`
# Subtract totallines with index
result=`expr $total - $index`
# Gives the desired output
grep -A $result "yahoo" filepath
Related
I am using Linux. I have a directory of many files, I want to use grep, tail and wildcard expansion * in tandem to print the last occurrence of <pattern> in each file:
Input: <some command>
Expected Output:
<last occurrence of pattern in file 1>
<last occurrence of pattern in file 2>
...
<last occurrence of pattern in file N>
What I am trying now is grep "pattern" * | tail -n 1 but the output contains only one line, which is the last occurrence of pattern in the last file. I assume the reason is because the * wildcard expansion happens before pipelining of commands, so the tail runs only once.
Does there exist some Bash syntax so that I can achieve the expected outcome, i.e. let tail run for each file?
I know I can always use a for-loop to solve the problem. I'm just curious if the problem can be solved with a more condensed command.
I've also tried grep -m1 "pattern" <(tac *), and it seems like the aforementioned reasoning still applies: wildcard expansion applies to only to the immediate command it is associated with, and the "outer" command runs only once.
Wildcards are expanded on the command line before any command runs. For example if you have files foo and bar in your directory and run grep pattern * | tail -n1 then bash transforms this into grep pattern foo bar | tail -n1 and runs that. Since there's only one stream of output from grep, there's only one stream of input to tail and it prints the last line of that stream.
If you want to search each file and print the last line of grep's output separately you can use a loop:
for file in * ; do
grep pattern "${file}" | tail -n1
done
The problem with non-loop solutions is that tail doesn't inherently know where the output of one file ends and the output of another file begins, or indeed that there are even files involved on the other end of the pipe. It just knows input is coming in from somewhere and it has to print the last line of that input. If you didn't want a loop, you'd have to use a more powerful tool like awk and perhaps use the fact that grep prepends the names of matched files (if multiple files are matched, or with -H) to delimit the start and end of outputs from each file. But, the work to write an awk program that keeps track of the current file to know when its output ends and print its last line is probably more effort than is worth when the loop solution is so simple.
You can achieve what you want using xargs. For your example it would be:
ls * | xargs -n 1 sh -c 'grep "pattern" $0 | tail -n 1'
Can save you from having to write a loop.
You can do this with awk, although (as tjm3772 pointed out in their answer) it's actually more complicated than the shell for loop. For the record, here's what I came up with:
awk -v pattern="YourPatternHere" '(FNR==1 && line!="") {print line; line=""}; $0~pattern {line=$0}; END {if (line!="") print line}'
Explanation: when it finds a matching line ($0~pattern), it stores that line in the line variable ({line=$0}) (this means that at the end of the file, line will hold the last matching line.
(Note: if you want to just include a literal pattern in the program, remove the -v pattern="YourPatternHere" part and replace $0~pattern with just /YourPatternHere/)
There's no simple trigger to print a match at the end of each file, so that part's split into two pieces: if it's the first line of a file AND line is set because of a match in the previous file ((FNR==1 && line!="")), print line and then clear it so it's not mistaken for a match in the current file ({print line; line=""}). Finally, at the end of the final file (END), print a match found in that last file if there was one ({if (line!="") print line}).
Also, note that the print-at-beginning-of-new-file test must be before the check for a matching line, or else it'll get very confused if the first line of the new file matches.
So... yeah, a shell for loop is simpler (and much easier to get right).
I have a fasta file with something like the following (amino acid sequences shortened for simplicity):
>nitrite_reductase
MYWGGPPAAWYGG
>ammonium_transporter
MWYY
I would like to keep all text between the first and second > signs and remove the second > and everything after it. I tried looking through the cut, awk, and sed documentation but couldn't find any immediately obvious ways of doing that. Any help would be appreciated!
With GNU sed, you can use
sed '1 n;/>/ Q' input.fasta
1 n; print the first line and go to the next
/>/ Q when the line matches >, end.
In other sed implementations, you can use
sed '1 n;/>/,$ d' input.fasta
Again, the first line is processed. From a later line matching > to the end the lines aren't printed.
Use this Perl one-liner:
perl -pe '$cnt++ if /^>/; last if $cnt > 1;' input.fasta
The Perl one-liner uses these command line flags:
-e : Tells Perl to look for code in-line, instead of in a file.
-p : Loop over the input one line at a time, assigning it to $_ by default. Add print $_ after each loop iteration.
$cnt++ if /^>/; : Initially, $cnt is undef, which in this context evaluates to 0. $cnt is incremented by 1 when a fasta header is encountered. So after the first header it sees, it becomes 1.
last if $cnt > 1; : Exit the loop (and the script) when $cnt is greater than 1, that is, at the second fasta header. Thus, the second sequence in the file, and the rest of them, is never printed. Even for large files, the exit happens quickly - right after the first sequence.
SEE ALSO:
perldoc perlrun: how to execute the Perl interpreter: command line switches
I have a text file which looks like this
1
bbbbb
aaa
END
2
ttttt
mmmm
uu
END
3
....
END
The number of lines between the single number patterns (1,2,3) and END is variable. So the upper delimiting pattern changes, but the final one does not. Using some bash commands, I would like to grep lines between a specified upper partner and the corresponding END, for example a command that takes as input 2 and returns
2
ttttt
mmmm
uu
END
I've tried various solutions with sed and awk, but still can't figure it out. The main problem is that I may need to grep a entry in the middle of the file, so I can't use sed with /pattern/q...Any help will be greatly appreciated!
With awk we set a flag f when matching the start pattern, which is an input argument. After that row, the flag is on and it prints every line. When reaching "END" (AND the flag is on!) it exits.
awk -v p=2 '$0~p{f=1} f{print} f&&/END/{exit}' file
Use sed and its addresses to only print a part of the file between the patterns:
#!/bin/bash
start=x
while [[ $start = *[^0-9]* ]] ; do
read -p 'Enter the start pattern: ' start
done
sed -n "/^$start$/,/^END$/p" file
You can use the sed with an address range. Modify the first regular expression (RE1) in /RE1/,/RE2/ as your convenience:
sed -n '/^[[:space:]]*2$/,/^[[:space:]]*END$/p' file
Or,
sed '
/^[[:space:]]*2$/,/^[[:space:]]*END$/!d
/^[[:space:]]*END$/q
' file
This quits upon reading the END, thus may be more efficient.
Another option/solution using just bash
#!/usr/bin/env bash
start=$1
while IFS= read -r lines; do
if [[ ${lines##* } == $start ]]; then
print=on
elif [[ ${lines##* } == [0-9] ]]; then
print=off
fi
case $print in on) printf '%s\n' "$lines";; esac
done < file.txt
Run the script with the number as the argument, 1 can 2 or 3 or ...
./myscript 1
This might work for you (GNU sed):
sed -n '/^\s*2$/{:a;N;/^\s*END$/M!ba;p;q}' file
Switch off implicit printing by setting the -n option.
Gather up the lines beginning with a line starting with 2 and ending in a line starting with END, print the collection and quit.
N.B. The second regexp uses the M flag, which allows the ^ and $ to match start and end of lines when multiple lines are being matched. Another thing to bear in mind is that using a range i.e. sed -n '/start/,/end/p' file, will start printing lines the moment the first condition is met and if the second match does not materialise, it will continue printing to the end of the file.
Having a file like foo.txt with content
1
2
3
4
5
How do i get the lines starting with 4 and 5 out of it (everything after last empty line), assuming the amount of lines can be different?
Updated
Let's try a slightly simpler approach with just sed.
$: sed -n '/^$/{g;D;}; N; $p;' foo.txt
4
5
-n says don't print unless I tell you to.
/^$/{g;D;}; says on each blank line, clear it all out with this:
g : Replace the contents of the pattern space with the contents of the hold space. Since we never put anything in, this erases the (possibly long accumulated) pattern space. Note that I could have used z since this is GNU, but I wanted to break it out for non-GNU sed's below, and in this case this works for both.
D : remove the now empty line from the pattern space, and go read the next.
Now previously accumulated lines have been wiped if (and only if) we saw a blank line. The D loops back to the beginning, so N will never see a blank line.
N : Add a newline to the pattern space, then append the next line of input to the pattern space. This is done on every line except blanks, after which the pattern space will be empty.
This accumulates all nonblanks until either 1) a blank is hit, which will clear and restart the buffer as above, or 2) we reach EOF with a buffer intact.
Finally, $p says on the LAST line (which will already have been added to the pattern space unless the last line was blank, which will have removed the pattern space...), print the pattern space. The only time this will have nothing to print is if the last line of the file was a blank line.
So the whole logic boils down to: clean the buffer on empty lines, otherwise pile the non-empty lines up and print at the end.
If you don't have GNU sed, just put the commands on separate lines.
sed -n '
/^$/{
g
D
}
N
$p
' foo.txt
Alternate
The method above is efficient, but could potentially build up a very large pattern buffer on certain data sets. If that's not an issue, go with it.
Or, if you want it in simple steps, don't mind more processes doing less work each, and prefer less memory consumed:
last=$( sed -n /^$/= foo.txt|tail -1 ) # find the last blank
next=$(( ${last:-0} + 1 )) # get the number of the line after
cmd="$next,\$p" # compose the range command to print
sed -n "$cmd" foo.txt # run it to print the range you wanted
This runs a lot of small, simple tasks outside of sed so that it can give sed the simplest, most direct and efficient description of the task possible. It will read the target file twice, but won't have to manage filling, flushing, and refilling the accumulation of data in the pattern buffer with records before a blank line. Still likely slower unless you are memory bound, I'd think.
Reverse the file, print everything up to the first blank line, reverse it again.
$ tac foo.txt | awk '/^$/{exit}1' | tac
4
5
Using GNU awk:
awk -v RS='\n\n' 'END{printf "%s",$0}' file
RS is the record separator set to empty line.
The END statement prints the last record.
try this:
tail +$(($(grep -nE ^$ test.txt | tail -n1 | sed -e 's/://g')+1)) test.txt
grep your input file for empty lines.
get last line with tail => 5:
remove unnecessary :
add 1 to 5 => 6
tail starting from 6
You can try with sed :
sed -n ':A;$bB;/^$/{x;s/.*//;x};H;n;bA;:B;H;x;s/^..//;p' infile
With GNU sed:
sed ':a;/$/{N;s/.*\n\n//;ba;}' file
Using grep, you can print lines that match your search query. Adding a -C option will print two lines of surrounding context, like this:
> grep -C 2 'lorem'
some context
some other context
**lorem ipsum**
another line
yet another line
Similarly, you can use grep -B 2 or grep -A 2 to print matching lines with two preceding or two following lines, respectively, for example:
> grep -A 2 'lorem'
**lorem ipsum**
another line
yet another line
Is it possible to skip the matching line and only print the context? Specifically, I would like to only print the line that is exactly 2 lines above a match, like this:
> <some magic command>
some context
If you can allow couple of grep instances to be used, you can try like as I mentioned in the comments section.
$ grep -v "lorem" < <(grep -A2 "lorem" file)
another line
yet another line
$ grep -A2 "lorem" file | grep -v "lorem"
another line
yet another line
If you are interested in a dose of awk, there is a cool way to do it as
$ awk -v count=2 '{a[++i]=$0;}/lorem/{for(j=NR-count;j<NR;j++)print a[j];}' file
another line
yet another line
It works by storing the entire file in its own array and after searching for the pattern lorem, the awk special variable which stores the row number(NR), points at the exact line in which the pattern is found. If we loop for 2 lines before it as dictated by the awk variable -v count, we can print the lines needed.
If you are interested in the printing the pattern also, just change the condition in for-loop as j<=NR instead of j<NR. That's it!
There’s no way to do this purely through a grep command. If there’s only one instance of lorem in the text, you could pipe the output through head.
grep -B2 lorem t | head -1
If there may be multiple occurrence of lorem, you could use awk:
awk '{second_previous=previous; previous=current_line; current_line=$0}; /lorem/ { print second_previous; }'
This awk command saves each line (along with the previous and the one before that) in variables so when it encounters a line containing lorem, it prints the second last line. If lorem happens to occur in the first or second line of the input, nothing would be printed.
awk, as others have said, is your friend here. You don't need complex loops or arrays or other junk, though; basic patterns suffice.
When you use -B N, (and the --no-group-separator flag) you get output in groups of M=N+1 lines. To select precisely one of those lines (in your question, you want the very first of the group), you can use modular arithmetic (tested with GNU awk).
awk -vm=3 -vx=1 'NR%m==x{print}'
You can think of the lines being numbered like this: they count up until you reach the match, at which point they go back to zero. So set m to N+1 and x to the line you want to extract.
1 some context
2 some other context
0 **lorem ipsum**
So the final command would be
grep -B2 --no-group-separator lorem $input | awk -vm=3 -vx=1 'NR%m==x{print}'