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(grep.info)Usage

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Usage
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   Here is an example shell command that invokes GNU `grep':

     grep -i 'hello.*world' menu.h main.c

This lists all lines in the files `menu.h' and `main.c' that contain
the string `hello' followed by the string `world'; this is because `.*'
matches zero or more characters within a line.  Note: Regular
Expressions.  The `-i' option causes `grep' to ignore case, causing
it to match the line `Hello, world!', which it would not otherwise
match.  Note: Invoking, for more details about how to invoke `grep'.

   Here are some common questions and answers about `grep' usage.

  1. How can I list just the names of matching files?

          grep -l 'main' *.c

     lists the names of all C files in the current directory whose
     contents mention `main'.

  2. How do I search directories recursively?

          grep -r 'hello' /home/gigi

     searches for `hello' in all files under the directory
     `/home/gigi'.  For more control of which files are searched, use
     `find', `grep' and `xargs'.  For example, the following command
     searches only C files:

          find /home/gigi -name '*.c' -print | xargs grep 'hello' /dev/null

  3. What if a pattern has a leading `-'?

          grep -e '--cut here--' *

     searches for all lines matching `--cut here--'.  Without `-e',
     `grep' would attempt to parse `--cut here--' as a list of options.

  4. Suppose I want to search for a whole word, not a part of a word?

          grep -w 'hello' *

     searches only for instances of `hello' that are entire words; it
     does not match `Othello'.  For more control, use `\<' and `\>' to
     match the start and end of words.  For example:

          grep 'hello\>' *

     searches only for words ending in `hello', so it matches the word
     `Othello'.

  5. How do I output context around the matching lines?

          grep -C 2 'hello' *

     prints two lines of context around each matching line.

  6. How do I force grep to print the name of the file?

     Append `/dev/null':

          grep 'eli' /etc/passwd /dev/null

  7. Why do people use strange regular expressions on `ps' output?

          ps -ef | grep '[c]ron'

     If the pattern had been written without the square brackets, it
     would have matched not only the `ps' output line for `cron', but
     also the `ps' output line for `grep'.

  8. Why does `grep' report "Binary file matches"?

     If `grep' listed all matching "lines" from a binary file, it would
     probably generate output that is not useful, and it might even
     muck up your display.  So GNU `grep' suppresses output from files
     that appear to be binary files.  To force GNU `grep' to output
     lines even from files that appear to be binary, use the `-a' or
     `--binary-files=text' option.  To eliminate the "Binary file
     matches" messages, use the `-I' or `--binary-files=without-match'
     option.

  9. Why doesn't `grep -lv' print nonmatching file names?

     `grep -lv' lists the names of all files containing one or more
     lines that do not match.  To list the names of all files that
     contain no matching lines, use the `-L' or `--files-without-match'
     option.

 10. I can do OR with `|', but what about AND?

          grep 'paul' /etc/motd | grep 'franc,ois'

     finds all lines that contain both `paul' and `franc,ois'.

 11. How can I search in both standard input and in files?

     Use the special file name `-':

          cat /etc/passwd | grep 'alain' - /etc/motd