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.
Related
I want to pass each output from a command as multiple argument to a second command, e.g.:
grep "pattern" input
returns:
file1
file2
file3
and I want to copy these outputs, e.g:
cp file1 file1.bac
cp file2 file2.bac
cp file3 file3.bac
How can I do that in one go? Something like:
grep "pattern" input | cp $1 $1.bac
You can use xargs:
grep 'pattern' input | xargs -I% cp "%" "%.bac"
You can use $() to interpolate the output of a command. So, you could use kill -9 $(grep -hP '^\d+$' $(ls -lad /dir/*/pid | grep -P '/dir/\d+/pid' | awk '{ print $9 }')) if you wanted to.
In addition to Chris Jester-Young good answer, I would say that xargs is also a good solution for these situations:
grep ... `ls -lad ... | awk '{ print $9 }'` | xargs kill -9
will make it. All together:
grep -hP '^\d+$' `ls -lad /dir/*/pid | grep -P '/dir/\d+/pid' | awk '{ print $9 }'` | xargs kill -9
For completeness, I'll also mention command substitution and explain why this is not recommended:
cp $(grep -l "pattern" input) directory/
(The backtick syntax cp `grep -l "pattern" input` directory/ is roughly equivalent, but it is obsolete and unwieldy; don't use that.)
This will fail if the output from grep produces a file name which contains whitespace or a shell metacharacter.
Of course, it's fine to use this if you know exactly which file names the grep can produce, and have verified that none of them are problematic. But for a production script, don't use this.
Anyway, for the OP's scenario, where you need to refer to each match individually and add an extension to it, the xargs or while read alternatives are superior anyway.
In the worst case (meaning problematic or unspecified file names), pass the matches to a subshell via xargs:
grep -l "pattern" input |
xargs -r sh -c 'for f; do cp "$f" "$f.bac"; done' _
... where obviously the script inside the for loop could be arbitrarily complex.
In the ideal case, the command you want to run is simple (or versatile) enough that you can simply pass it an arbitrarily long list of file names. For example, GNU cp has a -t option to facilitate this use of xargs (the -t option allows you to put the destination directory first on the command line, so you can put as many files as you like at the end of the command):
grep -l "pattern" input | xargs cp -t destdir
which will expand into
cp -t destdir file1 file2 file3 file4 ...
for as many matches as xargs can fit onto the command line of cp, repeated as many times as it takes to pass all the files to cp. (Unfortunately, this doesn't match the OP's scenario; if you need to rename every file while copying, you need to pass in just two arguments per cp invocation: the source file name and the destination file name to copy it to.)
So in other words, if you use the command substitution syntax and grep produces a really long list of matches, you risk bumping into ARG_MAX and "Argument list too long" errors; but xargs will specifically avoid this by instead copying only as many arguments as it can safely pass to cp at a time, and running cp multiple times if necessary instead.
The above will still work incorrectly if you have file names which contain newlines. Perhaps see also https://mywiki.wooledge.org/BashFAQ/020
#!/bin/bash
for f in files; do
if grep -q PATTERN "$f"; then
echo cp -v "$f" "${f}.bac"
fi
done
files can be *.txt or *.text which basically means files ending in *.txt or *text or replace with something that you want/need, of course replace PATTERN with yours. Remove echo if you're satisfied with the output. For a recursive solution take a look at the bash shell option globstar
I am using grep to get a list of files that I want to use for another grep search (and not simply piping it).
For example I got as an output:
file1.h:XXX: linecontent
file2.h:XXX: linecontent
file3.h:XXX: linecontent
file4.h:XXX: linecontent
and I want to grep only file1.h, file2.h ...
I'm assuming you want to search for files that contain two different patterns. If so this is what you want:
grep 'your pattern 2' `grep -l 'your pattern 1' *`
The contents of the back quotes will be executed first and the output substituted into the command line. Use of the -l flag will restrict the output of the grep command to just the file names.
If there are a very large number of files that match against your pattern 1 this could fail. The solution for that is to use xargs
grep -l 'your pattern 1' * | xargs grep 'your argument 2'
Assuming what you want is the names of files that contain 'lineofcontent', you could use:
grep -l 'lineofcontent' file*.h
I am trying to see if my nohup file contains the words that I am looking for. If it does, then I need to put that into tmp file.
So I am currently using:
if grep -q "Started|missing" $DIR3/$dirName/nohup.out
then
grep -E "Started|missing" "$DIR3/$dirName/nohup.out" > tmp
fi
But it never goes into the if statement even if there are words that I am looking for.
How can I fix this?
Since basic sed uses BRE, regex alternation operator is represented by \| . | matches a literal | symbol. And you don't need to touch | symbol in the grep which uses ERE.
if grep -q "Started\|missing" $DIR3/$dirName/nohup.out
You should use egrep instead of grep (Avinash Raj has explained that in other words already in his answer).
I would generally recommend using egrep as a default for everyday use (even though many expressions only contain the basic regular expression syntax). From a practical point the standard grep is only interesting for performance reasons.
Details about the advantages of grep vs. egrep can be found in that superuser question.
When you only put the grep results into the tmp-file, you do not want to grep the file twice.
You can not use
egrep "Started|missing" $DIR3/$dirName/nohup.out > tmp
since that would create an empty tmp file when nothing is found.
You can remove empty files with if [ ! -s tmp ] or use another solution:
Redirectong the grep results without grepping again can be done with
rm -f tmp 2>/dev/null
egrep "Started|missing" $DIR3/$dirName/nohup.out | while read -r strange_line; do
echo "${strange_line}" >> tmp
done
I have a directory which has many directories inside it with the pattern of their name as :
YYYYDDMM_HHMISS
Example: 20140102_120202
I want to extract only the YYYYDDMM part.
I tried ls -l|awk '{print $9}'|grep -o ^[0-9]* and got the answer.
However i have following questions:
Why doesnt this return any results: ls -l|awk '{print $9}'|grep -o [0-9]* . Infact it should have returned all the directories.
Strangely just including '^' before [0-9] works fine :
ls -l|awk '{print $9}'|grep -o ^[0-9]*
Any other(simpler) way to achieve the result?
Why doesnt this return any results: ls -l|awk '{print $9}'|grep -o [0-9]*
If there are files in your current directory that start with [0-9], then the shell will expand them before calling grep. For example, if I have two files a1, a2 and a3 and run this:
ls | grep a*
After the filenames are expanded, the shell will run this:
ls | grep a1 a2 a3
The result of which is that it will print the lines in a2 and a3 that match the text "a1". It will also ignore whatever is coming from stdin, because when you specify filenames for grep (2nd argument and beyond), it will ignore stdin.
Next, consider this:
ls | grep ^a*
Here, ^ has no special meaning to the shell, so it uses it verbatim. Since I don't have filenames starting with ^a, it will use ^a* as the pattern. If I did have filenames like ^asomething or ^another, then again, ^a* would be expanded to those filenames and grep would do something I didn't really intend.
This is why you have to quote search patterns, to prevent the shell from expanding them. The same goes for patterns in find /path -name 'pattern'.
As for a simpler way for what you want, I think this should do it:
ls | sed -ne 's/_.*//p'
To show only the YYDDMM part of the directory names:
for i in ./*; do echo $(basename "${i%%_*}"); done
Not sure what you want to do with it once you've got it though...
You must avoid parsing ls output.
Simple is to use this printf:
printf "%s\n" [0-9]*_[0-9]*|egrep -o '^[0-9]+'
How can I make use of grep in cygwin to find all files that contain BOTH words.
This is what I use to search all files in a directory recursively for one word:
grep -r "db-connect.php" .
How can I extend the above to look for files that contain both "db-connect.php" AND "version".
I tried this: grep -r "db-connect.php\|version" . but this is an OR i.e. it gets file that contain one or the other.
Thanks all for any help
grep -r db-connect.php . | grep version
If you want to grep for several strings in a file which have different lines, use the following command:
grep -rl expr1 | xargs grep -l expr2 | xargs grep -l expr3
This will give you a list of files that contain expr1, expr2, and expr3.
Note that if any of the file names in the directory contains spaces, these files will produce errors. This can be fixed by adding -0 I think to grep and xargs.
grep "db-connect.php" * | cut -d: -f1 | xargs grep "version"
I didn't try it in recursive mode but it should be the same.
To and together multiple searches, use multiple lookahead assertions, one per thing looked for apart from the last one:
instead of writing
grep -P A * | grep B
you write
grep -P '(?=.*A)B' *
grep -Pr '(?=.*db-connect\.php)version' .
Don’t write
grep -P 'A.*B|B.*A' *
because that fails on overlaps, whereas the (?=…)(?=…) technique does not.
You can also add in NOT operators as well. To search for lines that don’t match X, you normally of course use -v on the command line. But you can’t do that if it is part of a larger pattern. When it is, you add (?=(?!X).)*$) to the pattern to exclude anything with X in it.
So imagine you want to match lines with all three of A, B, and then either of C or D, but which don’t have X or Y in them. All you need is this:
grep -P '(?=^.*A)(?=^.*B)(?=^(?:(?!X).)*$)(?=^(?:(?!Y).)*$)C|D' *
In some shells and in some settings. you’ll have to escape the ! if it’s your history-substitution character.
There, isn’t that pretty cool?
In my cygwin the given answers didn't work, but the following did:
grep -l firststring `grep -r -l secondstring . `
Do you mean "string1" and "string2" on the same line?
grep 'string1.*string2'
On the same line but in indeterminate order?
grep '(string1.*string2)|(string2.*string1)'
Or both strings must appear in the file anywhere?
grep -e string1 -e string2
The uses PCRE (Perl-Compatible Regular Expressions) with multiline matching and returns the filenames of files that contain both strings (AND rather than OR).
grep -Plr '(?m)db-connect\.php(.*\n)*version|version(.*\n)*db-connect\.php' .
Why to stick to only grep:
perl -lne 'print if(/db-connect.php/&/version/)' *