I have a large file where each line contains a substring such as ABC123. If I execute
grep ABC file.txt
or
grep ABC1 file.txt
I get those lines back as expected, but if I execute
grep ABC12 file.txt
grep fails to find the corresponding lines.
This seems pretty trivial functionality, but I'm not a heavy user of grep so perhaps I'm missing some gotcha.
Use something like
od -x -a < filename
to dump out the file contents in hex. That'll immediately show you if what you have in your file is what you expect. Which I suspect it isn't :-)
Note: od has lots of useful options to help you here. Too many to list, in fact.
Is there a chance your file contains some hidden character, such as 0x00 ?
This doesn't make sense. Are you sure the file contains "ABC123"?
You can verify this by running following command in a shell
echo "ABC123" | grep ABC12
If the lines contain ABC123, then "grep ABC12" should get them. Do you perhaps mean that you want to match several different strings, such as ABC1, ABC2 and ABC3? In that case you can try this:
grep -E 'ABC1|ABC2|ABC3'
I'm not sure what the problem is.. grep works exactly as it should.. For example, the contents of my test file:
$ cat file.txt
ABC
ABC1
ABC12
ABC123
..and grep'ing for ABC, ABC1, ABC12, ABC123:
$ grep ABC file.txt
ABC
ABC1
ABC12
ABC123
$ grep ABC1 file.txt
ABC1
ABC12
ABC123
$ grep ABC12 file.txt
ABC12
ABC123
$ grep ABC123 file.txt
ABC123
grep is basically a filter, any line containing the first argument (ABC, or ABC1 etc) will be displayed. If it doesn't contain the entire string, it will not be displayed
Related
I am new to linux and I am experimenting with basic terminal commands. I found out that I can list all users using compgen -u but what if I only want to display the bottom line outputs ?
Ok lets say the output of compgen -u goes like this:
extra
extra
extra
extra
extra
extra
extra
extra
extra
John
William
Kate
Harold
I can only use grep to find a single text (ex. compgen -u | grep John). But what if I want to use grep to display John as well as all the remaining entries after it ?
sed or awk solution would be easier, but if you can only use grep, then the option --after-context (or -A) might do:
grep -A 5 John file
The drawback is that you need to know the number of lines to display after the matching (or use an arbitrary big number for the rest of the file).
compgen -u | grep -A$(compgen -u| wc -l) John
Explanation:
From man grep
-A NUM, --after-context=NUM
Print NUM lines of trailing context after matching lines. Places a line containing a group separator (described under --group-separator) between
contiguous groups of matches.
grep -A -- print number of rows after pattern
$() -- Execute unix command
compgen -u| wc -l --> Get total number of rows of output of command.
You can use the following one-liner :
n=$( compgen -u | grep -n John | head -1 | cut -d ":" -f 1 ) && compgen -u | tail -n +$n
This finds out the line number for first occurrence of John, and prints everything starting that line.
I need some help with a grep command (in the Bash).
In my source files, I want to list all unique parameters of a function. Background: I want to search through all files, to see, which permissions ([perm("abc")] are used.
Example.txt:
if (x) perm("this"); else perm("that");
perm("what");
I'd like to have my grep output:
this
that
what
If I do my grep with this search expression
perm\(\"(.*?)\"\)
I'll get perm("this), perm("that"), etc. but I'd like to have just the permissions: this and that and what.
How can I do that?
Use a look-behind:
$ grep -Po '(?<=perm\(")[^"]*' file
this
that
what
This looks for all the text occurring after perm(" and until another " is found.
Note -P is used to allow this behaviour (it is a Perl regex) and -o to just print the matched item, instead of the whole line.
Here is a gnu awk version (due to multiple characters in RS)
awk -v RS='perm\\("' -F\" 'NR>1 {print $1}' file
this
that
what
I have a file, for example, "queries.txt" that has hard return separated strings. I want to use this list to find matches in a second file, "biglist.txt".
"biglist.txt" may have multiple matches for each string in "queries.txt". I want to return only the first hit for each query and write this to another file.
grep -m 1 -wf queries.txt biglist.txt > output
only gives me one line in output. I should have output that is the same number of lines as queries.txt.
Any suggestions for this? Many thanks! I searched for past questions but did not find one that was exactly the same sort of case after a few minutes of reading.
If you want to "reset the counter" after each file, you could do
cat queries.txt | xargs -I{} grep -m 1 -w {} biglist.txt > output
This uses xargs to call grep once for each line in the input… should do the trick for you.
Explanation:
cat queries.txt - produce one "search word" per line
xargs -I{} - take the input one line at a time, and insert it at {}
grep -m 1 -w - find only one match of a whole word
{} - this is where xargs inserts the search term (once per call)
biglist.txt - the file to be searched
> output - the file where the result is to be written
An alternate method without xargs (which one should indeed learn):
(this method assumes there are no spaces in the lines in queries.txt)
cat queries.txt | while read target; do grep -m 1 $target biglist.txt; done > outr
I might not fully understand your question, but it sounds like something like this might work.
cat queries.txt | while read word; do grep "$word" biglist.txt | tee -a output.txt; done
Suppose I write a grep query to find out the occurrence of a method call on an object like this:
// might not be accurate, but irrelevant
grep -nr "[[:alnum:]]\.[[:alnum:]](.*)" .
This would give many results. How to find out how many such results are obtained?
What about using | wc -l to count the number of result lines?
What about
man grep | grep "count"
It outputs
-c, --count
Suppress normal output; instead print a count of matching lines for each input file. [...]
Previous answers are OK, I just want to put it into command line instructions in order to have copy-paste versions (from explicit to simplest) for the future:
grep --count "PATTERN" FILE
Is exactly the same as:
grep -c "PATTERN" FILE
And it is equivalent to:
grep "PATTERN" FILE | wc -l
As a bonus, below i give you a version where a file with a list of patterns is used.
grep -count --file=PATTERNFILE FILE
or simply
grep -cf PATTERNFILE FILE
I have a file that possibly contains bad formatting (in this case, the occurrence of the pattern \\backslash). I would like to use grep to return only the line numbers where this occurs (as in, the match was here, go to line # x and fix it).
However, there doesn't seem to be a way to print the line number (grep -n) and not the match or line itself.
I can use another regex to extract the line numbers, but I want to make sure grep cannot do it by itself. grep -no comes closest, I think, but still displays the match.
try:
grep -n "text to find" file.ext | cut -f1 -d:
If you're open to using AWK:
awk '/textstring/ {print FNR}' textfile
In this case, FNR is the line number. AWK is a great tool when you're looking at grep|cut, or any time you're looking to take grep output and manipulate it.
All of these answers require grep to generate the entire matching lines, then pipe it to another program. If your lines are very long, it might be more efficient to use just sed to output the line numbers:
sed -n '/pattern/=' filename
Bash version
lineno=$(grep -n "pattern" filename)
lineno=${lineno%%:*}
I recommend the answers with sed and awk for just getting the line number, rather than using grep to get the entire matching line and then removing that from the output with cut or another tool. For completeness, you can also use Perl:
perl -nE 'say $. if /pattern/' filename
or Ruby:
ruby -ne 'puts $. if /pattern/' filename
using only grep:
grep -n "text to find" file.ext | grep -Po '^[^:]+'
You're going to want the second field after the colon, not the first.
grep -n "text to find" file.txt | cut -f2 -d:
To count the number of lines matched the pattern:
grep -n "Pattern" in_file.ext | wc -l
To extract matched pattern
sed -n '/pattern/p' file.est
To display line numbers on which pattern was matched
grep -n "pattern" file.ext | cut -f1 -d: