So in Linux, less is used to read files page by page for better readability. I was wondering if you can do something like less file.txt > output.txt to get one page worth of file.txt and output/write it to `output.txt.
Apparently, this does not work, output.txt is exactly the same as the original file, I'm wondering why this is the case, and if there are other work-arounds. Thank you!
You can use the split command.
split -l 100 -d -a 3 input output
This will split the input file every 100 lines (-l 100), will use numbers as suffixes (-d) and will use 3 numbers as suffix (-a 3) in the output file. Something like this output000, output001, output002
You can use head to get a specific number of lines, and tput lines to see how many lines there are on your current terminal.
Here's a script that fetches a pageful, or the standard 25 lines if no terminal is available:
#!/bin/bash
lines=$(tput lines) || lines=25
head -n "$lines" file.txt > output.txt
we use head and tail to get n lines of top or bottom part of a file
cat /var/log/messages|tail -n20
head -n10 src/main.h
Is there a way to modify so that the tail -f lists the line number of the current file as well.
Something similar to grep -n <Strings> *.
Try less
Instead of using tail to follow data and less or nl for numbering, I suggest using a single tool for both:
less -N +F <filename>
This will make less print line numbers and follow the file. From man less:
F
Scroll forward, and keep trying to read when the end of file is reached. Normally this command would be used when already at the end of the file. It is a way to monitor the tail of a file which is growing while it is being viewed. (The behavior is similar to the tail -f command.)
You could do a Ctrl+C to stop following when inside less; to start following again, you could press F again. With this method, you get the additional goodies that less offers like regex-based search, tags, etc.
This command takes into account the number of lines above also
tail -f -n +1 yourfile.txt | nl
You can use less command,
tail -f <filename> | less -N
According to man page of less
-N or --LINE-NUMBERS
Causes a line number to be displayed at the beginning of each
line in the display.
Everything is in the title. Basicaly let's say I have this pattern
some text lalala
another line
much funny wow grep
I grep funny and I want my output to be "lalala"
Thank you
One possible answer is to use either ed or ex to do this (it is trivial in them):
ed - yourfile <<< 'g/funny/.-2p'
(Or replace ed with ex. You might have red, the restricted editor, too; it can't modify files.) This looks for the pattern /funny/ globally, and whenever it is found, prints the line 2 before the matching line (that's the .-2p part). Or, if you want the most recent line containing 'lalala' before the line matching 'funny':
ed - yourfile <<< 'g/funny/?lalala?p'
The only problem is if you're trying to process standard input rather than a file; then you have to save the standard input to a file and process that file, which spoils the concurrency.
You can't do negative offsets in sed (though GNU sed allows you to do positive offsets, so you could use sed -n '/lalala/,+2p' file to get the 'lalala' to 'funny' lines (which isn't quite what you want) based on finding 'lalala', but you cannot find the 'lalala' lines based on finding 'funny'). Standard sed does not allow offsets at all.
If you need to print just the IP address found on a line 8 lines before the pattern-matching line, you need a slightly more involved ed script, but it is still doable:
ed - yourfile <<< 'g/funny/.-8s/.* //p'
This uses the same basic mechanism to find the right line, then runs a substitute command to remove everything up to the last space on the line and print the modified version. Since there isn't a w command, it doesn't actually modify the file.
Since grep -B only prints each full number of lines before the match, you'll have to pipe the output into something like grep or Awk.
grep -B 2 "funny" file|awk 'NR==1{print $NF; exit}'
You could also just use Awk.
awk -v s="funny" '/[[:space:]]lalala$/{n=NR+2; o=$NF}NR==n && $0~s{print o}' file
For the specific example of an IP address 8 lines before the match as mentioned in your comment:
awk -v s="funny" '
/[[:space:]][0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$/ {
n=NR+8
ip=$NF
}
NR==n && $0~s {
print ip
}' file
These Awk solutions first find the output field you might want, then print the output only if the word you want exists in the nth following line.
Here's an attempt at a slightly generalized Awk solution. It maintains a circular queue of the last q lines and prints the line at the head of the queue when it sees a match.
#!/bin/sh
: ${q=8}
e=$1
shift
awk -v q="$q" -v e="$e" '{ m[(NR%q)+1] = $0 }
$0 ~ e { print m[((NR+1)%q)+1] }' "${#--}"
Adapting to a different default (I set it to 8) or proper option handling (currently, you'd run it like q=3 ./qgrep regex file) as well as remembering (and hence printing) the entire line should be easy enough.
(I also didn't bother to make it work correctly if you see a match in the first q-1 lines. It will just print an empty line then.)
Trying to debug an issue with a server and my only log file is a 20GB log file (with no timestamps even! Why do people use System.out.println() as logging? In production?!)
Using grep, I've found an area of the file that I'd like to take a look at, line 347340107.
Other than doing something like
head -<$LINENUM + 10> filename | tail -20
... which would require head to read through the first 347 million lines of the log file, is there a quick and easy command that would dump lines 347340100 - 347340200 (for example) to the console?
update I totally forgot that grep can print the context around a match ... this works well. Thanks!
I found two other solutions if you know the line number but nothing else (no grep possible):
Assuming you need lines 20 to 40,
sed -n '20,40p;41q' file_name
or
awk 'FNR>=20 && FNR<=40' file_name
When using sed it is more efficient to quit processing after having printed the last line than continue processing until the end of the file. This is especially important in the case of large files and printing lines at the beginning. In order to do so, the sed command above introduces the instruction 41q in order to stop processing after line 41 because in the example we are interested in lines 20-40 only. You will need to change the 41 to whatever the last line you are interested in is, plus one.
# print line number 52
sed -n '52p' # method 1
sed '52!d' # method 2
sed '52q;d' # method 3, efficient on large files
method 3 efficient on large files
fastest way to display specific lines
with GNU-grep you could just say
grep --context=10 ...
No there isn't, files are not line-addressable.
There is no constant-time way to find the start of line n in a text file. You must stream through the file and count newlines.
Use the simplest/fastest tool you have to do the job. To me, using head makes much more sense than grep, since the latter is way more complicated. I'm not saying "grep is slow", it really isn't, but I would be surprised if it's faster than head for this case. That'd be a bug in head, basically.
What about:
tail -n +347340107 filename | head -n 100
I didn't test it, but I think that would work.
I prefer just going into less and
typing 50% to goto halfway the file,
43210G to go to line 43210
:43210 to do the same
and stuff like that.
Even better: hit v to start editing (in vim, of course!), at that location. Now, note that vim has the same key bindings!
You can use the ex command, a standard Unix editor (part of Vim now), e.g.
display a single line (e.g. 2nd one):
ex +2p -scq file.txt
corresponding sed syntax: sed -n '2p' file.txt
range of lines (e.g. 2-5 lines):
ex +2,5p -scq file.txt
sed syntax: sed -n '2,5p' file.txt
from the given line till the end (e.g. 5th to the end of the file):
ex +5,p -scq file.txt
sed syntax: sed -n '2,$p' file.txt
multiple line ranges (e.g. 2-4 and 6-8 lines):
ex +2,4p +6,8p -scq file.txt
sed syntax: sed -n '2,4p;6,8p' file.txt
Above commands can be tested with the following test file:
seq 1 20 > file.txt
Explanation:
+ or -c followed by the command - execute the (vi/vim) command after file has been read,
-s - silent mode, also uses current terminal as a default output,
q followed by -c is the command to quit editor (add ! to do force quit, e.g. -scq!).
I'd first split the file into few smaller ones like this
$ split --lines=50000 /path/to/large/file /path/to/output/file/prefix
and then grep on the resulting files.
If your line number is 100 to read
head -100 filename | tail -1
Get ack
Ubuntu/Debian install:
$ sudo apt-get install ack-grep
Then run:
$ ack --lines=$START-$END filename
Example:
$ ack --lines=10-20 filename
From $ man ack:
--lines=NUM
Only print line NUM of each file. Multiple lines can be given with multiple --lines options or as a comma separated list (--lines=3,5,7). --lines=4-7 also works.
The lines are always output in ascending order, no matter the order given on the command line.
sed will need to read the data too to count the lines.
The only way a shortcut would be possible would there to be context/order in the file to operate on. For example if there were log lines prepended with a fixed width time/date etc.
you could use the look unix utility to binary search through the files for particular dates/times
Use
x=`cat -n <file> | grep <match> | awk '{print $1}'`
Here you will get the line number where the match occurred.
Now you can use the following command to print 100 lines
awk -v var="$x" 'NR>=var && NR<=var+100{print}' <file>
or you can use "sed" as well
sed -n "${x},${x+100}p" <file>
With sed -e '1,N d; M q' you'll print lines N+1 through M. This is probably a bit better then grep -C as it doesn't try to match lines to a pattern.
Building on Sklivvz' answer, here's a nice function one can put in a .bash_aliases file. It is efficient on huge files when printing stuff from the front of the file.
function middle()
{
startidx=$1
len=$2
endidx=$(($startidx+$len))
filename=$3
awk "FNR>=${startidx} && FNR<=${endidx} { print NR\" \"\$0 }; FNR>${endidx} { print \"END HERE\"; exit }" $filename
}
To display a line from a <textfile> by its <line#>, just do this:
perl -wne 'print if $. == <line#>' <textfile>
If you want a more powerful way to show a range of lines with regular expressions -- I won't say why grep is a bad idea for doing this, it should be fairly obvious -- this simple expression will show you your range in a single pass which is what you want when dealing with ~20GB text files:
perl -wne 'print if m/<regex1>/ .. m/<regex2>/' <filename>
(tip: if your regex has / in it, use something like m!<regex>! instead)
This would print out <filename> starting with the line that matches <regex1> up until (and including) the line that matches <regex2>.
It doesn't take a wizard to see how a few tweaks can make it even more powerful.
Last thing: perl, since it is a mature language, has many hidden enhancements to favor speed and performance. With this in mind, it makes it the obvious choice for such an operation since it was originally developed for handling large log files, text, databases, etc.
print line 5
sed -n '5p' file.txt
sed '5q' file.txt
print everything else than line 5
`sed '5d' file.txt
and my creation using google
#!/bin/bash
#removeline.sh
#remove deleting it comes move line xD
usage() { # Function: Print a help message.
echo "Usage: $0 -l LINENUMBER -i INPUTFILE [ -o OUTPUTFILE ]"
echo "line is removed from INPUTFILE"
echo "line is appended to OUTPUTFILE"
}
exit_abnormal() { # Function: Exit with error.
usage
exit 1
}
while getopts l:i:o:b flag
do
case "${flag}" in
l) line=${OPTARG};;
i) input=${OPTARG};;
o) output=${OPTARG};;
esac
done
if [ -f tmp ]; then
echo "Temp file:tmp exist. delete it yourself :)"
exit
fi
if [ -f "$input" ]; then
re_isanum='^[0-9]+$'
if ! [[ $line =~ $re_isanum ]] ; then
echo "Error: LINENUMBER must be a positive, whole number."
exit 1
elif [ $line -eq "0" ]; then
echo "Error: LINENUMBER must be greater than zero."
exit_abnormal
fi
if [ ! -z $output ]; then
sed -n "${line}p" $input >> $output
fi
if [ ! -z $input ]; then
# remove this sed command and this comes move line to other file
sed "${line}d" $input > tmp && cp tmp $input
fi
fi
if [ -f tmp ]; then
rm tmp
fi
You could try this command:
egrep -n "*" <filename> | egrep "<line number>"
Easy with perl! If you want to get line 1, 3 and 5 from a file, say /etc/passwd:
perl -e 'while(<>){if(++$l~~[1,3,5]){print}}' < /etc/passwd
I am surprised only one other answer (by Ramana Reddy) suggested to add line numbers to the output. The following searches for the required line number and colours the output.
file=FILE
lineno=LINENO
wb="107"; bf="30;1"; rb="101"; yb="103"
cat -n ${file} | { GREP_COLORS="se=${wb};${bf}:cx=${wb};${bf}:ms=${rb};${bf}:sl=${yb};${bf}" grep --color -C 10 "^[[:space:]]\\+${lineno}[[:space:]]"; }
I've got a strangely acting egrep -f.
Example:
$ egrep -f ~/tmp/tmpgrep2 orig_20_L_A_20090228.txt | wc -l
3
$ for lines in `cat ~/tmp/tmpgrep2` ; do egrep $lines orig_20_L_A_20090228.txt ; done | wc -l
12
Could someone give me a hint what could be the problem?
No, the files did not changed between executions. The expected answer for the egrep line count is 12.
UPDATE on file contents: the searched file contains cca 13000 lines, each of them are 500 char long, the pattern file contains 12 lines, each of them are 24 char long. The pattern always (and only) occurs on a fixed position in the seached file (26-49).
UPDATE on pattern contents: every pattern from tmpgrep2 are a 24 char long number.
If the search patterns are found on the same lines, then you can get the result you see:
Suppose you look for:
abc
def
ghi
jkl
and the data file is:
abcdefghijklmnoprstuvwxzy
then the one-time command will print 1 and the loop will print 4.
Could it be that the lines read contain something that the shell is expanding/substituting for you, in the second version? Then that doesn't get done by grep when it reads the patterns itself, thus leading to a different sent of patterns being matched.
I'm not totally sure if the shell is doing any expansion on the variable value in an invocation like that, but it's an idea at least.
EDIT: Nope, it doesn't seem to do any substitutions. But it could be quoting issue, if your patterns contain whitespace the for loop will step through each token, not through each line. Take a look at the read bash builtin.
Do you have any duplicates in ~/tmp/tmpgrep2? Egrep will only use the dupes one time, but your loop will use each occurrence.
Get rid of dupes by doing something like this:
$ for lines in `sort < ~/tmp/tmpgrep2 | uniq` ; do egrep $lines orig_20_L_A_20090228.txt ; done | wc -l
I second #unwind.
Why don't you run without wc -l and see what each search is finding?
And maybe:
for lines in `cat ~/tmp/tmpgrep2` ; do echo $lines ; done
Just to see now the shell is handling $lines?
The others have already come up with most of the things I would look at. The next thing I would check is the environment variable GREP_OPTIONS, or whatever it is called on your machine. I've gotten the strangest error messages or behaviors when using a command line argument that interfered with the environment settings.