Let's say I have two bash history files as follows:
history1.txt:
1 ls
2 cd foo
...
921 history > history1.txt
history2.txt:
154 vim /etc/nginx/nginx.conf
155 service nginx restart
...
1153 history > history2.txt
I knew I could easily write a bash script to merge these two files together so that the resulting file contains line 1 to 1153 without duplicate history entries... like the following bash scripts:
merge.sh
HEAD=`head -n 1 history2.txt | sed -e 's/^[[:space:]]*//'`
sed -n -e "1,/$HEAD/p" history1.txt > merged.txt
sed -e "1,$ s/$HEAD//" -e '/^\s*$/d' history2.txt >> merged.txt
But I spent way more time than I'd like to admit trying to find a way to accomplish this using only unnamed pipes, sed, and/ or any other common Linux utils WITHOUT variables and command substitution (`command`). I didn't have any success :(
Any Linux shell gurus or sed masters know if this is possible?
NOTE: I know the merge.sh script will not work for all edge cases.
If I understand that correct, you simply have 2 files with no duplicate entries (though not sure about it).
So you don't need sed or something here. Just:
cat history1.txt history2.txt | sort -n > output
If you have duplicates:
cat history1.txt history2.txt | sort -n -u > output
If I understand you want to add entries to your history file? Did you consider using the built in history -r ?
$ cat foo
echo "history"
$ history | tail -n 5
1371 rm foo
1372 tail .bash_history > foo
1373 vim foo
1374 cat foo
1375 history | tail
$ history -r foo
$ history | tail -n 5
1374 cat foo
1375 history | tail
1376 history -r foo
1377 echo "history"
1378 history | tail
Maybe give $ help history a look in case there is something that fits your needs.
You've got to learn the right tools to use to solve problems in UNIX as there are many wrong ways that LOOK like they solve a given problem but actually are slow, dangerous, non-portable, fragile, etc., etc.
sed is for simple substitutions on individual lines, that is all. shell is for manipulating files and processes and sequencing calls to UNIX tools, that is all. For general purpose text manipulation, the standard UNIX tool is awk.
The following is untested since you didn't provide sample input/output that we could run a tool against to test but it will be close if not exactly correct:
awk '
NR==FNR {file1[$1]=$0;next}
{
for (i=(prev+1); i<$1; i++) {
print file1[i]
}
print
prev = $1
}
' history1.txt history2.txt
if you create the flie like this
1 ls
2 cd foo
921 history > history1.txt
154 vim /etc/nginx/nginx.conf
155 service nginx restart
1153 history >> history1.txt
now everything, both historys, are in 1 file.
use the cut command to select only the command lines end cut out the line numbes like. (-d is for cutting on spaces, -f is for selecting from colum 4 till the end)
cut -d " " -f 4- histroy1.txt > temp.txt
now you have all the commands in one document in the temp.txt file.
if you then use sort and uniqe to like
sort temp.txt |uniq
you get all the uniq commands you used in the 2 history files in 1 file.
Related
Is that possible to use grep on a continuous stream?
What I mean is sort of a tail -f <file> command, but with grep on the output in order to keep only the lines that interest me.
I've tried tail -f <file> | grep pattern but it seems that grep can only be executed once tail finishes, that is to say never.
Turn on grep's line buffering mode when using BSD grep (FreeBSD, Mac OS X etc.)
tail -f file | grep --line-buffered my_pattern
It looks like a while ago --line-buffered didn't matter for GNU grep (used on pretty much any Linux) as it flushed by default (YMMV for other Unix-likes such as SmartOS, AIX or QNX). However, as of November 2020, --line-buffered is needed (at least with GNU grep 3.5 in openSUSE, but it seems generally needed based on comments below).
I use the tail -f <file> | grep <pattern> all the time.
It will wait till grep flushes, not till it finishes (I'm using Ubuntu).
I think that your problem is that grep uses some output buffering. Try
tail -f file | stdbuf -o0 grep my_pattern
it will set output buffering mode of grep to unbuffered.
If you want to find matches in the entire file (not just the tail), and you want it to sit and wait for any new matches, this works nicely:
tail -c +0 -f <file> | grep --line-buffered <pattern>
The -c +0 flag says that the output should start 0 bytes (-c) from the beginning (+) of the file.
In most cases, you can tail -f /var/log/some.log |grep foo and it will work just fine.
If you need to use multiple greps on a running log file and you find that you get no output, you may need to stick the --line-buffered switch into your middle grep(s), like so:
tail -f /var/log/some.log | grep --line-buffered foo | grep bar
you may consider this answer as enhancement .. usually I am using
tail -F <fileName> | grep --line-buffered <pattern> -A 3 -B 5
-F is better in case of file rotate (-f will not work properly if file rotated)
-A and -B is useful to get lines just before and after the pattern occurrence .. these blocks will appeared between dashed line separators
But For me I prefer doing the following
tail -F <file> | less
this is very useful if you want to search inside streamed logs. I mean go back and forward and look deeply
Didn't see anyone offer my usual go-to for this:
less +F <file>
ctrl + c
/<search term>
<enter>
shift + f
I prefer this, because you can use ctrl + c to stop and navigate through the file whenever, and then just hit shift + f to return to the live, streaming search.
sed would be a better choice (stream editor)
tail -n0 -f <file> | sed -n '/search string/p'
and then if you wanted the tail command to exit once you found a particular string:
tail --pid=$(($BASHPID+1)) -n0 -f <file> | sed -n '/search string/{p; q}'
Obviously a bashism: $BASHPID will be the process id of the tail command. The sed command is next after tail in the pipe, so the sed process id will be $BASHPID+1.
Yes, this will actually work just fine. Grep and most Unix commands operate on streams one line at a time. Each line that comes out of tail will be analyzed and passed on if it matches.
This one command workes for me (Suse):
mail-srv:/var/log # tail -f /var/log/mail.info |grep --line-buffered LOGIN >> logins_to_mail
collecting logins to mail service
Coming some late on this question, considering this kind of work as an important part of monitoring job, here is my (not so short) answer...
Following logs using bash
1. Command tail
This command is a little more porewfull than read on already published answer
Difference between follow option tail -f and tail -F, from manpage:
-f, --follow[={name|descriptor}]
output appended data as the file grows;
...
-F same as --follow=name --retry
...
--retry
keep trying to open a file if it is inaccessible
This mean: by using -F instead of -f, tail will re-open file(s) when removed (on log rotation, for sample).
This is usefull for watching logfile over many days.
Ability of following more than one file simultaneously
I've already used:
tail -F /var/www/clients/client*/web*/log/{error,access}.log /var/log/{mail,auth}.log \
/var/log/apache2/{,ssl_,other_vhosts_}access.log \
/var/log/pure-ftpd/transfer.log
For following events through hundreds of files... (consider rest of this answer to understand how to make it readable... ;)
Using switches -n (Don't use -c for line buffering!).By default tail will show 10 last lines. This can be tunned:
tail -n 0 -F file
Will follow file, but only new lines will be printed
tail -n +0 -F file
Will print whole file before following his progression.
2. Buffer issues when piping:
If you plan to filter ouptuts, consider buffering! See -u option for sed, --line-buffered for grep, or stdbuf command:
tail -F /some/files | sed -une '/Regular Expression/p'
Is (a lot more efficient than using grep) a lot more reactive than if you does'nt use -u switch in sed command.
tail -F /some/files |
sed -une '/Regular Expression/p' |
stdbuf -i0 -o0 tee /some/resultfile
3. Recent journaling system
On recent system, instead of tail -f /var/log/syslog you have to run journalctl -xf, in near same way...
journalctl -axf | sed -une '/Regular Expression/p'
But read man page, this tool was built for log analyses!
4. Integrating this in a bash script
Colored output of two files (or more)
Here is a sample of script watching for many files, coloring ouptut differently for 1st file than others:
#!/bin/bash
tail -F "$#" |
sed -une "
/^==> /{h;};
//!{
G;
s/^\\(.*\\)\\n==>.*${1//\//\\\/}.*<==/\\o33[47m\\1\\o33[0m/;
s/^\\(.*\\)\\n==> .* <==/\\o33[47;31m\\1\\o33[0m/;
p;}"
They work fine on my host, running:
sudo ./myColoredTail /var/log/{kern.,sys}log
Interactive script
You may be watching logs for reacting on events?
Here is a little script playing some sound when some USB device appear or disappear, but same script could send mail, or any other interaction, like powering on coffe machine...
#!/bin/bash
exec {tailF}< <(tail -F /var/log/kern.log)
tailPid=$!
while :;do
read -rsn 1 -t .3 keyboard
[ "${keyboard,}" = "q" ] && break
if read -ru $tailF -t 0 _ ;then
read -ru $tailF line
case $line in
*New\ USB\ device\ found* ) play /some/sound.ogg ;;
*USB\ disconnect* ) play /some/othersound.ogg ;;
esac
printf "\r%s\e[K" "$line"
fi
done
echo
exec {tailF}<&-
kill $tailPid
You could quit by pressing Q key.
you certainly won't succeed with
tail -f /var/log/foo.log |grep --line-buffered string2search
when you use "colortail" as an alias for tail, eg. in bash
alias tail='colortail -n 30'
you can check by
type alias
if this outputs something like
tail isan alias of colortail -n 30.
then you have your culprit :)
Solution:
remove the alias with
unalias tail
ensure that you're using the 'real' tail binary by this command
type tail
which should output something like:
tail is /usr/bin/tail
and then you can run your command
tail -f foo.log |grep --line-buffered something
Good luck.
Use awk(another great bash utility) instead of grep where you dont have the line buffered option! It will continuously stream your data from tail.
this is how you use grep
tail -f <file> | grep pattern
This is how you would use awk
tail -f <file> | awk '/pattern/{print $0}'
I have more than 50000 files in a directory such as file1.txt, file2.txt, ....., file50000.txt. I would like to concatenate of some files whose file numbers are listed in the following text file (need.txt).
need.txt
1
4
35
45
71
.
.
.
I tried with the following. Though it is working, but I look for more simpler and short way.
n1=1
n2=$(wc -l < need.txt)
while [ $n1 -le $n2 ]
do
f1=$(awk 'NR=="$n1" {print $1}' need.txt)
cat file$f1.txt >> out.txt
(( n1++ ))
done
This might also work for you:
sed 's/.*/file&.txt/' < need.txt | xargs cat > out.txt
Something like this should work for you:
sed -e 's/.*/file&.txt/' need.txt | xargs cat > out.txt
It uses sed to translate each line into the appropriate file name and then hands the filenames to xargs to hand them to cat.
Using awk it could be done this way:
awk 'NR==FNR{ARGV[ARGC]="file"$1".txt"; ARGC++; next} {print}' need.txt > out.txt
Which adds each file to the ARGV array of files to process and then prints every line it sees.
It is possible do it without any sed or awk command. Directly using bash built-in functions and cat (of course).
for i in $(cat need.txt); do cat file${i}.txt >> out.txt; done
And as you want, it is quite simple.
I know that I can use `` to get the output of a command, for example:
echo `ls`
but is there a way for me to use the ls command first and then run echo on it? For example: ls <some special redirection> echo? I tried ls > echo and it does not do what I want.
The reason I am asking is that sometimes I write complicated commands to get certain output for example: bjobs -u username01 | grep normal | awk '{print $1}' is a simple "complicated" command (sometimes they are 6 or 7 changed together). Now, I am currently having to do
Mycommand `(complicated string of commands)`
but I would much rather just do
(complicated string of commands) <some special redirection> Mycommand
is this possible?
You may use xargs
ls | xargs echo
When you need more actions on your result, you can parse them:
Parsing ls should be avoided, just rewriting the example:
ls | while read file; do
echo I found ${file}
done
This construction can be useful for more difficult parsing:
echo "red ford 2012
blue mustang 1998" | while read color car year; do
echo "My ${color} ${car} is from the year ${year}"
done
I have a Linux driver running in the background that is able to return the current system data/stats. I view the data by running a console utility (let's call it dump-data) in a console. All data is dumped every time I run dump-data. The output of the utility is like below
Output:
- A=reading1
- B=reading2
- C=reading3
- D=reading4
- E=reading5
...
- variableX=readingX
...
The list of readings returned by the utility can be really long. Depending on the scenario, certain readings would be useful while everything else would be useless.
I need a way to grep only the useful readings whose names might have have nothing in common (via a bash script). I.e. Sometimes I'll need to collect A,D,E; and other times I'll need C,D,E.
I'm attempting to graph the readings over time to look for trends, so I can't run something like this:
# forgive my pseudocode
Loop
dump-data | grep A
dump-data | grep D
dump-data | grep E
End Loop
to collect A,D,E as that would actually give me readings from 3 separate calls of dump-data as that would not be accurate.
If you want to save all result of grep in the same file, you can just join all expressions in one:
grep -E 'expr1|expr2|expr3'
But if you want to have results (for expr1, expr2 and expr3) in separate files, things are getting more interesting.
You can do this using tee >(command).
For example, here I process the same pipe with thre different commands:
$ echo abc | tee >(sed s/a/_a_/ > file1) | tee >(sed s/b/_b_/ > file2) | sed s/c/_c_/ > file3
$ grep "" file[123]
file1:_a_bc
file2:a_b_c
file3:ab_c_
But the command seems to be too complex.
I would better save dump-data results to a file and then grep it.
TEMP=$(mktemp /tmp/dump-data-XXXXXXXX)
dump-data > ${TEMP}
grep A ${TEMP}
grep B ${TEMP}
grep C ${TEMP}
You can use dump-data | grep -E "A|D|E". Note the -E option of grep. Alternatively you could use egrep without the -E option.
you can simply use:
dump-data | grep -E 'A|D|E'
awk '/MY PATTERN/{print > "matches-"FILENAME;}' myfile{1,3}
thx Guru at Stack Exchange
I have few log files around 100MBs each.
Personally I find it cumbersome to deal with such big files. I know that log lines that are interesting to me are only between 200 to 400 lines or so.
What would be a good way to extract relavant log lines from these files ie I just want to pipe the range of line numbers to another file.
For example, the inputs are:
filename: MyHugeLogFile.log
Starting line number: 38438
Ending line number: 39276
Is there a command that I can run in cygwin to cat out only that range in that file? I know that if I can somehow display that range in stdout then I can also pipe to an output file.
Note: Adding Linux tag for more visibility, but I need a solution that might work in cygwin. (Usually linux commands do work in cygwin).
Sounds like a job for sed:
sed -n '8,12p' yourfile
...will send lines 8 through 12 of yourfile to standard out.
If you want to prepend the line number, you may wish to use cat -n first:
cat -n yourfile | sed -n '8,12p'
You can use wc -l to figure out the total # of lines.
You can then combine head and tail to get at the range you want. Let's assume the log is 40,000 lines, you want the last 1562 lines, then of those you want the first 838. So:
tail -1562 MyHugeLogFile.log | head -838 | ....
Or there's probably an easier way using sed or awk.
I saw this thread when I was trying to split a file in files with 100 000 lines. A better solution than sed for that is:
split -l 100000 database.sql database-
It will give files like:
database-aaa
database-aab
database-aac
...
And if you simply want to cut part of a file - say from line 26 to 142 - and input it to a newfile :
cat file-to-cut.txt | sed -n '26,142p' >> new-file.txt
How about this:
$ seq 1 100000 | tail -n +10000 | head -n 10
10000
10001
10002
10003
10004
10005
10006
10007
10008
10009
It uses tail to output from the 10,000th line and onwards and then head to only keep 10 lines.
The same (almost) result with sed:
$ seq 1 100000 | sed -n '10000,10010p'
10000
10001
10002
10003
10004
10005
10006
10007
10008
10009
10010
This one has the advantage of allowing you to input the line range directly.
If you are interested only in the last X lines, you can use the "tail" command like this.
$ tail -n XXXXX yourlogfile.log >> mycroppedfile.txt
This will save the last XXXXX lines of your log file to a new file called "mycroppedfile.txt"
This is an old thread but I was surprised nobody mentioned grep. The -A option allows specifying a number of lines to print after a search match and the -B option includes lines before a match. The following command would output 10 lines before and 10 lines after occurrences of "my search string" in the file "mylogfile.log":
grep -A 10 -B 10 "my search string" mylogfile.log
If there are multiple matches within a large file the output can rapidly get unwieldy. Two helpful options are -n which tells grep to include line numbers and --color which highlights the matched text in the output.
If there is more than file to be searched grep allows multiple files to be listed separated by spaces. Wildcards can also be used. Putting it all together:
grep -A 10 -B 10 -n --color "my search string" *.log someOtherFile.txt