How to use grep to find strings begin with hypen(-)?

Question

For example:

man perl | grep '-w'

only to receive error messages

man perl | grep -- '-w'

anubhava
– anubhava

2017-06-26 07:02:59 +00:00
Commented Jun 26, 2017 at 7:02 — anubhava
– anubhava, Commented Jun 26, 2017 at 7:02
man perl | grep -F "-w"

Shiwangini
– Shiwangini

2020-03-28 15:54:03 +00:00
Commented Mar 28, 2020 at 15:54 — Shiwangini
– Shiwangini, Commented Mar 28, 2020 at 15:54

Roman Cheplyaka · Accepted Answer · 2017-06-26 08:27:23Z

4

Use the double hyphen:

% man perl | grep -- '-w'                                                                                                                                                                    
       The "use warnings" pragma produces some lovely diagnostics. One can also use the -w flag, but its use is normally discouraged, because it gets applied to all executed Perl code,

This usage of -- is recommended by the POSIX standard:

The first -- argument that is not an option-argument should be accepted as a delimiter indicating the end of options. Any following arguments should be treated as operands, even if they begin with the - character.

edited Jun 26, 2017 at 8:27

answered Jun 26, 2017 at 7:03

Roman Cheplyaka

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3 Comments

Morris Li Over a year ago

Thank you very much

Morris Li Over a year ago

Could you provide some references about the usage of '--'?

Roman Cheplyaka Over a year ago

@MuYuanLi: added

tso · Accepted Answer · 2017-06-26 09:18:09Z

2

or just escape - character:

man perl | grep '\-w'

output:

   also use the -w flag, but its use is normally discouraged, because it

answered Jun 26, 2017 at 9:18

tso

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Comments

Zach · Accepted Answer · 2017-06-26 07:18:26Z

1

Use -- to give a parameter which starts with - .

MacBook-Pro:~ chen$ man perl | grep -- '-w'
       also use the -w flag, but its use is normally discouraged, because it
MacBook-Pro:~ chen$

In most bash builtin & some other commands, the -- means the end of options. By the same token, you can delete a file which name is -f.txt using this command:

MacBook-Pro:tmp chen$ rm -fv -- -f.txt 
-f.txt
MacBook-Pro:tmp chen$

answered Jun 26, 2017 at 7:18

Zach

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2 Comments

Morris Li Over a year ago

Thanks, could you provide some refferences on when and how to use '--'?

Zach Over a year ago

man getopt : The getopt utility will place `--' in the arguments at the end of the options, or recognize it if used explicitly.

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