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 

?

Answer 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

• egrep mini tutorial

References

• regular-expressions.info/Flavor comparison
  • Flavor note for GNU grep, ed, sed, egrep, awk, emacs
    • Lists the differences between grep vs egrep vs other regex flavors

Answer 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