LinuxQuestions.org - fgrep help please

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fgrep help please

Can you please give me information about fgrep?
What does the following command do?

Code:

grep -f file1 file2

What is the difference between fgrep and grep -f as well as Fgrep and grep -F?

If I want to print common lines between two files, how can I do this with grep?

Quote:

Originally Posted by bloodstreetboy (Post 4934662)

What does the following command do?

Code:

grep -f file1 file2

If I want to print common lines between two files, how can I do this with grep?

Have you tried the command you mentioned? It does exactly what you ask for.

The grep manual page answers all your (other) questions.

Yes I have tried this command.
I have two files with following contents.
The file process.txt have

Code:

 12:24:37 up 59 min,  6 users,  load average: 0.58, 1.64, 1.89      thunderbird back-up

USER    TTY      FROM              LOGIN@  IDLE  JCPU  PCPU WHAT

root    tty7    :0              11:25  59:16  1:14  0.21s gnome-session      jmeter test plans

root    pts/2    :0.0            11:30  19:54  0.01s  0.01s bash

root    pts/3    :0.0            11:30  52:36  0.16s  0.16s bash

root    pts/4    :0.0            11:32  51:14  28:42  28:42  ffmpeg -i /medi

root    pts/5    :0.0            11:33  50:28  29:05  29:05  ffmpeg -i /medi

root    pts/6    :0.0            11:56    0.00s  0.01s  0.00s w      Test material



May 11 15:31

============

/root - 6.3G - 1,06,342/ 4.4G - 98277

 .cpan - 331.9MB - 50056

 .cache- 495.5MB - 555

/usr  - 5.7G

/var - 1.2G

/tmp - 68.7K

/sys - 545.9M

/selinux - nothing

/sbin - 7.4M

/proc - 1016.8M

/opt - 1.3G /1.3G-81243

/lost+found - nothing

/lib - 634.9M

/home - 51.6M

/etc - 26.4M

/dev - 960M

/boot - 97.1M

/bin - 6.2M

& the file space.txt have

Code:

May 11 15:31

============

/root - 6.3G - 1,06,342/ 4.4G - 98277

 .cpan - 331.9MB - 50056

 .cache- 495.5MB - 555

/usr  - 5.7G

/var - 1.2G

/tmp - 68.7K

/sys - 545.9M

/selinux - nothing

/sbin - 7.4M

/proc - 1016.8M

/opt - 1.3G /1.3G-81243

/lost+found - nothing

/lib - 634.9M

/home - 51.6M

/etc - 26.4M

/dev - 960M

/boot - 97.1M

/bin - 6.2M

======================================

Jul 14 19:43

============

File system

  Desktop

  Documents

  /opt - htdocs + database

  thunderbird back-up

  

    Demo Projects

    htdocs

    jmeter test plans

    Management

    thunderbird back-up

    Test cases for projects

    Test material



16 GB

  Empty

73 GB

  Empty

==================================================

Remove

------

Eclipse

Netbeans

Seamonkey

The out put of
$ grep -f process.txt space.txt
is same as
cat space.txt

I am not able to understand why does not it print common lines.

Quote:

Originally Posted by bloodstreetboy (Post 4934736)

Yes I have tried this command.
I have two files with following contents.

The output of
$ grep -f process.txt space.txt
is same as
cat space.txt

I am not able to understand why does not it print common lines.

The grep command posted is the 'typical' solution. However, it does produce the same results for me on openSUSE (and a diff confirms it...it's essentially cat'ing a file).

So...options:

The diff command:

Code:

diff --changed-group-format='%=' process.txt space.txt
Using sort and comm:

Code:

sort -o tmp1 process.txt sort -o tmp2 space.txt comm -12 tmp1 tmp2
A Perl one-liner:

Code:

perl -ne"print if s/^-//"

fgrep is equivalent to grep -F, not grep -f

Code:

~$ fgrep <keyword> file1 file2        ## Same as grep -F

~$ grep -F <keyword> file1 file2      ## Same as fgrep

Whereas grep -f is used to specify file as argument. From manual of grep (see here):

Code:

-f FILE, --file=FILE

      Obtain patterns from FILE, one per line. The empty file con-

      tains zero patterns, and therefore matches nothing.

@TB0ne & @shivaa
Thanks for your explanation. I got it.
I think I should use diff or comm to print common lines, that would be much better.
Thanks again.