grep: repetition-operator operand invalid

Question

I have this regular express `(?<=heads/)(.*?)(?=
)` and you can see it working here http://regexr.com?347dm I need this regex to work in the grep command but I'm getting this error. ``` $ grep -Eio '(?<=heads/)(.*?)(?=
)' text.txt grep: repetition-operator operand invalid ``` It works great in ack but I dont have ack on the machine I need to run this on. ``` ack text.txt -o --match '(?<=heads/)(.*?)(?=
)' ``` text.txt ``` 74f3649af36984e1b784e46502fe318e91d29570 HEAD 06d4463ab47a6246e6bd94dc3b9267d59fc16c2e refs/heads/ARC 0597e13c22b6397a1b260951f9d064f668b26f08 refs/heads/LocationAge e7e1ed942d15efb387c878b9d0335b37560c8807 refs/heads/feature/311-312-breaking-banner-updates d0b2632b465702d840a358d0b192198ae505011c refs/heads/gulf-news 509173eafc6792739787787de0d23b0c804d4593 refs/heads/jbb-new-applicationdidfinishlaunching 1e7b03ce75b1a7ba47ff4fb5128bc0bf43a7393b refs/heads/locationdebug 74f3649af36984e1b784e46502fe318e91d29570 refs/heads/master 5d2ede384325877c24db7ba1ba0338dc…

Accepted Answer

```
$ grep -Pio '(?<=heads/)(.*?)(?=
)' text.txt # P option instead of E
```

If you use GNU grep, you can use `-P` or `--perl-regexp` options.

In case you are using OS X, you need to install GNU grep.

```
$ brew install grep 
```

Due to recent changes, to use GNU grep on macOS you either have to prepend the command with a 'g'

```
$ ggrep -Pio '(?<=heads/)(.*?)(?=
)' text.txt # P option instead of E
```

Or change the path name

grep: repetition-operator operand invalid

Solution

Problem