Tutorial :Pattern matching digits does not work in egrep?



Question:

Why can't I match the string

"1234567-1234567890"  

with the given regular expression

\d{7}-\d{10}  

with egrep from the shell like this:

egrep \d{7}-\d{10} file  

?


Solution:1

egrep doesn't recognize \d shorthand for digit character class, so you need to use e.g. [0-9].

Moreover, while it's not absolutely necessary in this case, it's good habit to quote the regex to prevent misinterpretation by the shell. Thus, something like this should work:

egrep '[0-9]{7}-[0-9]{10}' file  

See also

References


Solution:2

For completeness:

Egrep does in fact have support for character classes. The classes are:

  • [:alnum:]
  • [:alpha:]
  • [:cntrl:]
  • [:digit:]
  • [:graph:]
  • [:lower:]
  • [:print:]
  • [:punct:]
  • [:space:]
  • [:upper:]
  • [:xdigit:]

Example (note the double brackets):

egrep '[[:digit:]]{7}-[[:digit:]]{10}' file  


Solution:3

you can use \d if you pass grep the "perl regex" option, ex:

grep -P "\d{9}"


Solution:4

Use [0-9] instead of \d. egrep doesn't know \d.


Solution:5

try this one:

egrep '(\d{7}-\d{10})' file  

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