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how can I extract a log based on specific time frame? Let's say issue started between 4pm to 5pm, how can I get that specific log between those times? I can use less or cat or grep but it would not give me the details of the error, sample command:
grep "2013-08-26 16:00:00" sample.log
what is the more precise Linux/ Unix command that can do the trick?
For viewing ERROR log messages between 16:00:00 and 17:00:00 use:
grep -nP '2013-08-15 16:.+ERROR' sample.log | less
If you have multiline messages in log you can use -A n and -B n params to add for each output string n lines after or before:
3 lines before and after each line:
grep -A 3 -B 3 -nP '2013-08-15 16:.+ERROR' sample.log | less
Shorthand for the same:
grep -3 -nP '2013-08-15 16:.+ERROR' sample.log | less
If you know that issue happened between 4 and 5 pm, you can use this:
grep "2013-08-26 16:" sample.log | less
If you need some lines around that issue, add option -N to grep (context of N lines), something like that:
grep -3 "2013-08-26 16:" sample.log | less
If you know that your event contained some specific word, you can filter it more using one more grep:
grep -3 "2013-08-26 16:" sample.log | grep somethingelse
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I know what the commands ls and wc do, but I can not find out what ls > wc and ls | wc will show. Can someone please help me flush out the meaning of this commands?
ls | wc The output from the ls command is piped into the wc command. So it will count the words which are in the output of ls. So you see simply the number of files read by ls.
ls > wc This creates a new file in your current working directory with the name wc with the output of your ls command. The program wc is not used here, simply a new file with the same name is created. You can simply look into this new file with your favorite editor or simply use cat for it.
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How to list only numerical directory names in Linux.
Only directories, that has only numeric characters?
There are multiple solutions to do it.
1.You can List just dirs and then remove . and / from the names and then Grep just numerical ones:
ls -d ./*/ | sed 's/\.\///g' | sed 's/\///g' | grep -E '^[0-9]+$'
2.By "ls" & "grep" & then "awk". Just list with details, Grep dirs and then Print 9th column:
ls -llh | grep '^d' | awk '{print $9}'
Good luck In Arbaeen.
In bash, you can benefit from extended globbing:
shopt -s extglob
ls -d +([0-9])/
Where
+(pattern-list)
Matches one or more occurrences of the given patterns
The / at the end limits the list to directories, and -d prevents ls from listing their contents.
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My friend just passed me this command to count the number of files in a directory:
$ ls -lt | wc -l
Can someone please help me flush out the meaning of this command? I know that ls is to list all the files. But what does -lt mean?
Also, I get a different count if I use ls | wc -l with no -lt option. Why is that the case?
You'll want to get familiar with the "man (manual) pages":
$ man ls
In this case you'll see:
-l (The lowercase letter ``ell''.) List in long format. (See below.) If
the output is to a terminal, a total sum for all the file sizes is
output on a line before the long listing.
-t Sort by time modified (most recently modified first) before sorting the
operands by lexicographical order.
Another way you can see the effect of the options is to run ls without piping to the wc command. Compare
$ ls
with
$ ls -l
and
$ ls -lt
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To count the number of files in a directory, I typically use
ls directory | wc -l
But is there another command that doesn't use wc ?
this is one:
ls -l . | egrep -c '^-'
Note:
ls -1 | wc -l
Which means:
ls: list files in dir
-1: (that's a ONE) only one entry per line. Change it to -1a if you want hidden files too
|: pipe output onto...
wc: "wordcount"
-l: count lines.
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This does not generate any output. How come?
$ echo 'this 1 2 3' | grep '\d\+'
But these do:
$ echo 'this 1 2 3' | grep '\s\+'
this 1 2 3
$ echo 'this 1 2 3' | grep '\w\+'
this 1 2 3
As specified in POSIX, grep uses basic regular expressions, but \d is part of a Perl-compatible regular expression (PCRE).
If you are using GNU grep, you can use the -P option, to allow use of PCRE regular expressions. Otherwise you can use the POSIX-specified [[:digit:]] character class in place of \d.
echo 1 | grep -P '\d'
# output: 1
echo 1 | grep '[[:digit:]]'
# output: 1
Try this $ echo 'this 1 2 3' | grep '[0-9]\+'