Ubuntu – Problems with “+” in grep

command linegrepregex

I'm trying to write a grep command to find lines like the below in a large text file:

<div class="node_thumbnail" data-type="file" name="GOPR0036.MP4_frame000001.jpg" data="813334c25191468c9f1c57afc99fde60" aid="133948" rel="/Files/ToolTipView?fileId=813334c25191468c9f1c57afc99fde60&pageNo=1&NoCache=101016083044" rev="topMiddle">

but the + symbol seems to be causing problems in the below commands:

 grep 'data=[a-z,0-9,\"]' file

Lots of hits

 grep 'data=[a-z,0-9,\"]+' file

No hits

Best Answer

If you want + to mean "one or more of the preceding atom", then you have to do one of:

Use -E (Extended Regular Expressions) (or -P, PCRE):
```
grep -E 'data=[a-z,0-9,\"]+' file
```
Escape + so that is treated specially in the Basic Regular Expressions used by default in grep:
```
grep 'data=[a-z,0-9,"]\+' file
```

Related Solutions

Ubuntu – grep pattern with leading spaces

Your line 2 and 3 has upper case P and requires zero or more spaces, so specify exactly that:

$ grep '[[:blank:]]*Pattern'  input.txt                                  
 Pattern to be recognized
         Pattern to be recognized here also

Personally, I'd recommend extending your pattern with something else, like '[[:blank:]]Pattern.*recognized'

Ubuntu – How to include a space character with grep

Make sure you quote your expression.

$ grep ' \.pdf' example
grep .pdf

Or if there might be multiple spaces (we can't use * as this will match the cases where there are no preceding spaces)

grep ' \+\.pdf' example

+ means "one or more of the preceding character". In BRE you need to escape it with \ to get this special function, but you can use ERE instead to avoid this

grep -E ' +\.pdf' example

You can also use \s in grep to mean a space

grep '\s\+\.pdf' example

We should escape literal . because in regex . means any character, unless it's in a character class.

Best Answer

Related Solutions

Ubuntu – grep pattern with leading spaces

Ubuntu – How to include a space character with grep

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