Matching arbitrary number of digits using grep regex - regex

Question

I've got a file that has lines in it that look similar as follows
data
datalater
983290842
Data387428later
datafhj893724897290384later
4329804928later
What I am looking to do is use regex to match any line that starts with data and ends with later AND has numbers in between. Here is what I've concocted so far:
^[D,d]ata[0-9]*later$
However the output includes all datalater lines. I suppose I could pipe the output and grep -v datalater, but I feel like a single expression should do the trick.

Answer 1

Use + instead of *.
+ matches at least one or more of the preceding.
* matches zero or more.
^[Dd]ata[0-9]+later$
In grep you need to escape the +, and we can use \d which is a character class and matches single digits.
^[Dd]ata\d\+later$
In you example file you also have a line:
datafhj893724897290384later
This currently will not be matched due to there being letters in-between data and the numbers. We can fix this by adding a [^0-9]* to match anything after data until the digits.
Our final command will be:
grep '^[Dd]ata[^0-9]*\d\+later$' filename

Answer 2

Using Cygwin, the above commands didn't work. I had to modify the commands given above to get the desired results.
$ cat > file.txt <<EOL
> data
> datalater
> 983290842
> Data387428later
> datafhj893724897290384later
> 4329804928later
> EOL
I always like to make sure my file has what I expect it to have:
$ cat file.txt
data
datalater
983290842
Data387428later
datafhj893724897290384later
4329804928later
$
I needed to run Perl-style expressions with the -P flag. This meant I couldn't use the [^0-9]+, whose necessity #Tom_Cammann aptly pointed out. Instead, I used .* which matches any sequence of characters not matching the next part of the pattern. Here are my command and output.
$ grep -P '^[Dd]ata.*\d+later$' file.txt
Data387428later
datafhj893724897290384later
$
I wish I could give a better explanation of WHY Perl expressions are needed, but I just know that Cygwin's grep works a bit differently.
System Info
$ uname -a
CYGWIN_NT-10.0 A-1052207 2.5.2(0.297/5/3) 2016-06-23 14:29 x86_64 Cygwin
My Results from the previous answers
$ grep '^[Dd]ata[^0-9]*\d\+later$' file2.txt
$ grep '^[Dd]ata\d+later$' file2.txt
$ grep -P '^[Dd]ata[^0-9]*\d\+later$' file2.txt
$ grep -P '^[Dd]ata\d+later$' file2.txt
Data387428later
$

Answer 3

You're matching zero or more digits with the * qualifier. Try
^[Dd]ata\d+later$
instead. You were also finding commas at the beginning of the string (e.g. ",ata1234later"). And \d is a shortcut to finding any digit character. So I changed those as well.

Answer 4

You should put a "+" (which means one or several) instead of "*" (which means zero, one or several

Answer 5

The "+" syntax only works for extended-regexp, not standard grep.
At least, that's my experience on RHEL.
To use extended-regexp, run egrep or pass "-E" / "--extended-regexp"
Examples...
Standard grep
echo abc123n1 | grep "abc[0-9]+n1"
<no output>
egrep
echo abc123n1 | egrep "abc[0-9]+n1"
abc123n1
grep with -E
echo abc123n1 | grep -E "abc[0-9]+n1"
abc123n1
HTH

Answer 6

grep -Eio "^(data)[0-9]+(later)$"
^[dD]ata=^d later$=r$

Answer 7

🎯 MOTIVATION
The rest of answers don't work on all systems.
🗒️ REQUISITES
grep
The option: --extended-regexp
Character groups, aka: [:group:]
Matching one or more of the preceding, aka: +
Optionally setting as starting or ending: ^whatever$
📟 COMMAND
grep --extended-regexp "[[:group:]]+"
🗂️ GROUPS
alnum
alpha
blank
cntrl
digit
graph
lower
print
punct
space
upper
xdigit