LinuxQuestions.org - How to grep for string "->"

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How to grep for string "->"

It seems easy, but I can't seem to do a `grep "->" input`. I would like to be able to do this within backticks in perl where the input for grep is stored in a variable $variable or @variable e.g. `@variable | grep "->"`.

The error I am currently getting is because no matter how I specify ->, grep thinks I am trying to specify the option -> which is, of course, not valid.

EDIT: I found that in my case, I only needed to use ">", however, I am still interested in how to grep for a pattern starting with a "-". Also, whenever I use @variable within backticks in perl, even if I follow it with a pipe, it tries to execute all the lines of that variable as commands instead of piping them to the grep/awk/etc.

grep -e '->'

the -e means that the next argument is the pattern, and won't be interpreted as an argument.

remember, you can always use a backslash in unix
to fix such stuff,

Code:

grep \-\> file

but WHY are you using grep in a perl script?

post what you are trying to do.

For whatever reason, grep takes \- as an argument just as much as it takes - or "-". So the example you posted:

Code:

grep \-\> file

still errors out with:

Code:

grep: invalid option -- '>'

Usage: grep [OPTION]... PATTERN [FILE]...

Try `grep --help' for more information.

Unless I'm mistaken (which is always a distinct possibility!), the \ only makes sure the character gets past the shell, and actually gets passed to the program, instead of being interpreted by the shell. For example,

Code:

echo This is a & test

Will interpret the & and split the line into two distinct processes, where

Code:

echo This is a \& test

will pass "This is a & test" to the echo command. So as far as grep is concerned, - and \- are the same thing.

OK, so...

What I have gleaned is:

The backslash is interpreted by the shell as escaping the next character, which then gets passed literally to the program (without the backslash). So:

Code:

# Both the '-' and '>' are escaped in the shell, but the '-' is passed unescaped

# to grep, which interprets -> as an invalid option

rob@rob-laptop:~$ echo $var | grep \-\>

grep: invalid option -- > 

Usage: grep [OPTION]... PATTERN [FILE]...

Try `grep --help' for more information.

# The '\' is escaped in the shell, so '\->' gets passed to grep.

# It interprets the pattern correctly.

rob@rob-laptop:~$ echo $var | grep \\-\> 

$this->cheese 

# The '>' is now no longer escaped in the shell,

# so bash throws an error

rob@rob-laptop:~$ echo $var | grep \\-\\> 

bash: syntax error near unexpected token `newline' 

# The quotes protect the pattern from the shell, but not from grep

rob@rob-laptop:~$ echo $var | grep '->' 

grep: invalid option -- >

Usage: grep [OPTION]... PATTERN [FILE]...

Try `grep --help' for more information.

bash: echo: write error: Broken pipe

# The quotes protect the '>', the backslash then escapes the '-' for grep

rob@rob-laptop:~$ echo $var | grep '\->' 

$this->cheese

# '--' means "no more options"

rob@rob-laptop:~$ echo $var | grep -- '->' 

$this->cheese

oops

grep '\-\>' file