[SOLVED] grep: can't find options in manfile

andrew.comly · 12-01-2015, 09:57 PM

I can find whole words in manfiles with the grep command, but I can't find options.

I have a manfile: /home/a/manfiles/grep.man. I would like to use grep to find the option "-F".

My failed attempts:

Code:

1)  $ grep -n '--text' /home/a/manfiles/grep.man

2)  $ grep '-F, ' ~/manfiles/grep.man
grep: invalid option -- ','
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.

3)  $ grep -n '-F, ' ~/manfiles/grep.man
grep: invalid option -- ','
Usage: grep [OPTION]... PATTERN [FILE]...
Try 'grep --help' for more information.

4)  $ grep -w -F ~/manfiles/grep.man 
^C

5)  $ grep -n '-F' ~/manfiles/grep.man
^C

6)  $ grep -n "-F" /home/a/manfiles/grep.man
^C

7)  $ grep -f '-F' /home/a/manfiles/grep.man
grep: -F: No such file or directory

8)  $ grep -f /home/a/manfiles/grep.man '-F'
^C

9)  $ grep -fwr '-F' /home/a/manfiles/grep.man
grep: wr: No such file or directory

10)  $ grep -wrf '-F' /home/a/manfiles/grep.man
grep: -F: No such file or directory

I have succeeded in finding words, e.g.

Code:

a@a-X200MA:/media/a/Sea_ext4/Calculus/Ch07$ grep -n '\<PATTERN\>' /home/a/manfiles/grep.man 
9:       grep [OPTIONS] PATTERN [FILE...]
10:       grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]
15:       containing  a  match  to the given PATTERN.  By default, grep prints the
36:              Interpret  PATTERN  as  an  extended regular expression (ERE, see
40:              Interpret PATTERN as  a  list  of  fixed  strings,  separated  by
45:              Interpret PATTERN as a basic regular expression (BRE, see below).
49:              Interpret PATTERN as a Perl regular expression (PCRE, see below).
54:       -e PATTERN, --regexp=PATTERN
55:              Use PATTERN as the pattern.  This can be used to specify multiple
65:              Ignore case distinctions in both the PATTERN and the input files.

Why can't grep find anything starting with a hyphen ("-F")?

andrew.comly · 12-01-2015, 10:13 PM

I finally got it!

Code:

$ grep -n '\-F' /home/a/manfiles/grep.man
19:       available.  egrep is the same as grep -E.  fgrep is the same as grep -F.
39:       -F, --fixed-strings
41:              newlines,  any  of  which  is to be matched.  (-F is specified by

It seems that symbol "-" is quite particular and necessitates the use of a backslash in order to negate(turn off) it's special nature. But of course this shows that my understanding of single quotes isn't quite right.

I wonder why in Bash Beginners Guide, p31 it is written "Single quotes ('...') are used to preserve the literal value of each character enclosed within the quotes", but in reality you still must use a backslash. Wouldn't that be a contradiction?

syg00 · 12-01-2015, 10:22 PM

Nope - it does retain its literal value, but gets passed to grep as an option - just like the other options (preceded with a hyphen).
Use "--" to end options, then pass in anything with a leading hyphen that is not an option.

This is general for bash, not specific to grep.

ntubski · 12-02-2015, 10:29 AM

Quote:

Originally Posted by syg00

This is general for bash, not specific to grep.

It's not implemented by bash, grep and many other programs do follow this convention.