Grep does not show results, online regex tester does -

i unexperienced behavior of grep. have bunch of xml files contain lines these:

<identifier type="abc">abc:def.ghi/g1234.ab012345</identifier> <identifier type="abc">abc:def.ghi/g5678m.ab678901</identifier> 

i wanted identifier part after slash , constructed regex using regexpal:

[a-z]\d{4}[a-z]*\.[a-z]*\d* 

it highlights wanted. perfect. when run grep on same file, don't results. , said, don't know grep, tried different combinations.

grep [a-z]\d{4}[a-z]*\.[a-z]*\d* test.xml grep "[a-z]\d{4}[a-z]*\.[a-z]*\d*" test.xml egrep "[a-z]\d{4}[a-z]*\.[a-z]*\d*" test.xml grep '[a-z]\d{4}[a-z]*\.[a-z]*\d*' test.xml grep -e '[a-z]\d{4}[a-z]*\.[a-z]*\d*' test.xml 

what doing wrong?

your regex doesn't match input. let's break down:

• [a-z] matches g
• \d{4} matches 1234
• [a-z]* doesn't match 5

also, believe grep , family don't \d syntax. try either [0-9] or [:digit:]

finally, when using regular expressions, prefer egrep grep. don't remember exact details, egrep supports more regex operators. also, in many shells (including bash on os x mentioned, use single quotes instead of double quotes, otherwise * expanded shell list of files in current directory before grep sees (and other shell meta-characters expanded too). bash won't touch in single quotes.