CODEWITHSUNDEEP
pythonregexgrep
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Reputation: 23

Different result between grep and python with the same regex statement

Why the same regex statement, get different result between Python and grep?

My input string is like as below:

statement or comment should appear in default case [MISRA 2012 Rule 16.1, required], [MISRA 2012 Rule 16.4, required]

The purpose is to find [MISRA 2012 Rule 16.1, required] and [MISRA 2012 Rule 16.4, required] by regex.

Using the code as below in Python, 

onelineStr = "statement or comment should appear in default case [MISRA 2012 Rule 16.1, required], [MISRA 2012 Rule 16.4, required]"
r1 = re.findall(r"\[MISRA.*?\]", onelineStr)
print (r1)

the result is shown as below, which is as my expectation.

['[MISRA 2012 Rule 16.1, required]', '[MISRA 2012 Rule 16.4, required]']

However, when I use the same statement of regex in grep. Nothing I can find.

grep -o --color "\[MISRA.*?\]" 1.txt

The content of 1.txt is statement or comment should appear in default case [MISRA 2012 Rule 16.1, required], [MISRA 2012 Rule 16.4, required]

Is anything wrong?

Thank you!!

Upvotes: 1

Views: 176

Answers (1)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 626952

The .*? lazy dot pattern matches any 0 or more chars (other than line break chars) as few as possible, but lazy quantifiers are not supported in POSIX regular expressions.

You need to use a [^][]* in grep in a POSIX BRE pattern to match zero or more chars other than ] and [:

grep -o --color "\[MISRA[^][]*]" 1.txt

Actually, the same pattern can be used in Python re, too.

[^][]* is an example of "smart placement" of special chars inside a bracket expression (POSIX bracket expressions do not allow regex escape sequences).

Upvotes: 2

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