How to suppress patterns being treated as options in grep

Question

In grep, when I try to find a pattern in the man page, the pattern is treated as the option of grep if it starts with -. For example, I find someone is using uname -r and I wonder what does -r means for uname.

 uname --help | grep '-r'

But I got the following error,

Usage: grep [OPTION]... PATTERN [FILE]... Try `grep --help' for more information.

Seems as if -r is treated as an option for grep.

score 4 · Accepted Answer · answered Oct 05 '14 at 20:29

There are two ways:

If supported by your version, use -- to stop argument processing.
```
uname --help | grep -- '-r'
```
Use the -e option to specify the pattern. Since it expects an argument, grep will not treat the next string as a new option just because it starts with a hyphen.
```
uname --help | grep -e '-r'
```

score 4 · Answer 2 · answered Oct 05 '14 at 20:31

As described in the man page for grep:

-e PATTERN, --regexp=PATTERN

Use PATTERN as the pattern. This can be used to specify multiple search patterns, or to protect a pattern beginning with a hyphen (-). (-e is specified by POSIX.)

uname --help | grep -e -r does what is expected.

score 1 · Answer 3 · answered Oct 05 '14 at 21:57

1

Backslash also seems to help:

uname --help | grep "\-r"
uname --help | grep '\-r'

answered Oct 05 '14 at 21:57

Vytenis Bivainis

2,308
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interesting, escape the - – Peng Zhang Oct 05 '14 at 21:58

How to suppress patterns being treated as options in grep

3 Answers3