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DᴀʀᴛʜVᴀᴅᴇʀ
Asked: 2015-08-23 17:02:17 +0800 CST

Why is my repetition condition with grep range not working?

  • 772

Searched for a solution on SO, Ask and Unix/Linux but I am lost trying to figure out how to write a conditional with a grep range:

Go through:

1-20_something
100-200_something
2-100_something
11-333_something

code works but only on 1-9_something:

if grep -q '[0-9]-[0-9]_something' "$foobar"; then
    echo "Additional Code"
fi

doesn't work:

if grep -q '\d{1,3}-\d{1,3}_something' "$foobar"; then
    echo "Additional Code"
fi

and this doesn't work:

if grep -q '[0-9]{1,3}-[0-9]{1,3}_something' "$foobar"; then
    echo "Additional Code"
fi

What is the best way to range through {1,3}?

EDIT:

To help the next person that may run across this I did a lot of searching and after the answers given I was able to result:

command-line

2 Answers

  1. Best Answer

    Curly brackets { } are treated as literals in BRE (Basic Regular Expression). From man grep:

       Basic vs Extended Regular Expressions
       In  basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their
       special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).

    So you need either 

    grep '[0-9]\{1,3\}-[0-9]\{1,3\}_something'

    or enable Extended Regular Expression mode with the -E switch

    grep -E '[0-9]{1,3}-[0-9]{1,3}_something'
    • 3

  2. Your second attempt should work if you enabled PCRE (Perl-compatible regular expressions) using -P:

    grep -Pq '\d{1,3}-\d{1,3}_something'

    \d is not in BRE or ERE or in the list of extra backslash expressions that GNU Grep has, but it is a Perl thing.

    Your third attempt should work if you enabled ERE (extended regular expressions):

    grep -Eq '[0-9]{1,3}-[0-9]{1,3}_something'

    <exp>{m,n} is not a BRE (basic regular expression) construct.

    • 2