How can I grep all lines starting by a specific letter (for instance "n")in a file ?
for the file /var/log/messages, I tried
# cat /var/log/messages | grep n*
it didn't work
All lines starting with n:
cat /var/log/messages | grep "^n"
use regular expressions for pattern
^ Indicates the beginning of an input string
$ Indicates the end of an input string
cat /var/log/messages | grep ^n
Have a look at https://www.linux.com/topic/desktop/introduction-regular-expressions-new-linux-users/
Related
I want to grep line.
Example I have #chargen in file and i want to command to grep output this word with #
cat /etc/inetd.conf | grep '*#' chargen
no result, any idea
How can I apply the following command to only a part of a text file? For example from the beginning to the line 5000.
grep "^ A : 11 B : 10" filename | wc -l
I cannot use head and then apply the above command since the text file is huge.
You could try using the sed command, which I believe does better for large files, from this question and pipe to grep.
sed -n 1,5000p file | grep ...
You can try combination of -n (prefixing each line of output with line number) and -m (limiting number of matching lines). Something like this:
grep -n -m 5000 pattern file.txt | grep -B 5000 "^5000:" | wc -l
First grep search for pattern, add line numbers and limit output to first 5000 matching lines (worst case scenario: all lines from range match pattern). Second grep match line number 5000, and print all lines before this line.
I don't know if it is more efficient solution
askljasklj.
twuikso lsliosus.
sakjsiua .sfdds* askhkjash.
Here I want to grep lines containing .* pattern.
Using command cat file | grep ".\*" is giving output sakjsiua .sfdds* askhkjash, but this should not be output or I am using the wrong command
Can anyone help here?
I assume that you have the words in a file foo. Hence giving a command:
cat foo | grep ".*"
Would print everything. If you just want .* pattern then use the below command:
cat foo | grep "\.\*"
By putting \ we can making . and * to behave as a normal text character
you should escape them both as below:
grep "\.\*" yourfile
Basically I'm wondering why this doesn't output anything:
tail --follow=name file.txt | grep something | grep something_else
You can assume that it should produce output I have run another line to confirm
cat file.txt | grep something | grep something_else
It seems like you can't pipe the output of tail more than once!? Anyone know what the deal is and is there a solution?
EDIT:
To answer the questions so far, the file definitely has contents that should be displayed by the grep. As evidence if the grep is done like so:
tail --follow=name file.txt | grep something
Output shows up correctly, but if this is used instead:
tail --follow=name file.txt | grep something | grep something
No output is shown.
If at all helpful I am running ubuntu 10.04
You might also run into a problem with grep buffering when inside a pipe.
ie, you don't see the output from
tail --follow=name file.txt | grep something > output.txt
since grep will buffer its own output.
Use the --line-buffered switch for grep to work around this:
tail --follow=name file.txt | grep --line-buffered something > output.txt
This is useful if you want to get the results of the follow into the output.txt file as rapidly as possible.
Figured out what was going on here. It turns out that the command is working it's just that the output takes a long time to reach the console (approx 120 seconds in my case). This is because the buffer on the standard out is not written each line but rather each block. So instead of getting every line from the file as it was being written I would get a giant block every 2 minutes or so.
It should be noted that this works correctly:
tail file.txt | grep something | grep something
It is the following of the file with --follow=name that is problematic.
For my purposes I found a way around it, what I was intending to do was capture the output of the first grep to a file, so the command would be:
tail --follow=name file.txt | grep something > output.txt
A way around this is to use the script command like so:
script -c 'tail --follow=name file.txt | grep something' output.txt
Script captures the output of the command and writes it to file, thus avoiding the second pipe.
This has effectively worked around the issue for me, and I have explained why the command wasn't working as I expected, problem solved.
FYI, These other stackoverflow questions are related:
Trick an application into thinking its stdin is interactive, not a pipe
Force another program's standard output to be unbuffered using Python
You do know that tail starts by default with the last ten lines of the file? My guess is everything the cat version found is well into the past. Try tail -n+1 --follow=name file.txt to start from the beginning of the file.
works for me on Mac without --follow=name
bash-3.2$ tail delme.txt | grep po
position.bin
position.lrn
bash-3.2$ tail delme.txt | grep po | grep lr
position.lrn
grep pattern filename | grep pattern | grep pattern | grep pattern ......
How do I pipe the output of grep as the search pattern for another grep?
As an example:
grep <Search_term> <file1> | xargs grep <file2>
I want the output of the first grep as the search term for the second grep. The above command is treating the output of the first grep as the file name for the second grep. I tried using the -e option for the second grep, but it does not work either.
You need to use xargs's -i switch:
grep ... | xargs -ifoo grep foo file_in_which_to_search
This takes the option after -i (foo in this case) and replaces every occurrence of it in the command with the output of the first grep.
This is the same as:
grep `grep ...` file_in_which_to_search
Try
grep ... | fgrep -f - file1 file2 ...
If using Bash then you can use backticks:
> grep -e "`grep ... ...`" files
the -e flag and the double quotes are there to ensure that any output from the initial grep that starts with a hyphen isn't then interpreted as an option to the second grep.
Note that the double quoting trick (which also ensures that the output from grep is treated as a single parameter) only works with Bash. It doesn't appear to work with (t)csh.
Note also that backticks are the standard way to get the output from one program into the parameter list of another. Not all programs have a convenient way to read parameters from stdin the way that (f)grep does.
I wanted to search for text in files (using grep) that had a certain pattern in their file names (found using find) in the current directory. I used the following command:
grep -i "pattern1" $(find . -name "pattern2")
Here pattern2 is the pattern in the file names and pattern1 is the pattern searched for
within files matching pattern2.
edit: Not strictly piping but still related and quite useful...
This is what I use to search for a file from a listing:
ls -la | grep 'file-in-which-to-search'
Okay breaking the rules as this isn't an answer, just a note that I can't get any of these solutions to work.
% fgrep -f test file
works fine.
% cat test | fgrep -f - file
fgrep: -: No such file or directory
fails.
% cat test | xargs -ifoo grep foo file
xargs: illegal option -- i
usage: xargs [-0opt] [-E eofstr] [-I replstr [-R replacements]] [-J replstr]
[-L number] [-n number [-x]] [-P maxprocs] [-s size]
[utility [argument ...]]
fails. Note that a capital I is necessary. If i use that all is good.
% grep "`cat test`" file
kinda works in that it returns a line for the terms that match but it also returns a line grep: line 3 in test: No such file or directory for each file that doesn't find a match.
Am I missing something or is this just differences in my Darwin distribution or bash shell?
I tried this way , and it works great.
[opuser#vjmachine abc]$ cat a
not problem
all
problem
first
not to get
read problem
read not problem
[opuser#vjmachine abc]$ cat b
not problem xxy
problem abcd
read problem werwer
read not problem 98989
123 not problem 345
345 problem tyu
[opuser#vjmachine abc]$ grep -e "`grep problem a`" b --col
not problem xxy
problem abcd
read problem werwer
read not problem 98989
123 not problem 345
345 problem tyu
[opuser#vjmachine abc]$
You should grep in such a way, to extract filenames only, see the parameter -l (the lowercase L):
grep -l someSearch * | xargs grep otherSearch
Because on the simple grep, the output is much more info than file names only. For instance when you do
grep someSearch *
You will pipe to xargs info like this
filename1: blablabla someSearch blablabla something else
filename2: bla someSearch bla otherSearch
...
Piping any of above line makes nonsense to pass to xargs.
But when you do grep -l someSearch *, your output will look like this:
filename1
filename2
Such an output can be passed now to xargs
I have found the following command to work using $() with my first command inside the parenthesis to have the shell execute it first.
grep $(dig +short) file
I use this to look through files for an IP address when I am given a host name.