I am using grep to match lines which have exactly 52 pipelines (|). The grep command I am using is:
grep -nP "^(.*?\|){52}"
-P because the lazy modifier ? does not work otherwise. When I run this, the following message is displayed: PCRE's backtracking limit is exceeded. I guess there is something wrong with perl-like regex here.
Thanks a lot!
Your PCRE pattern (that only matches 52 occurrences of any 0+ chars, as few as possible, up to and including | char, and does not check any text beyond that) contains a repeated capturing group, when the engine matches, it also places each 0+ chars before each | and the | char into a group, and then re-writes the value upon each iteration. In some implementations, it causes the error you provided.
Note you do not need a PCRE regex for the task since to match any char but | you may use [^|] and then use a mere POSIX ERE pattern (enabled with -E option) with grep:
grep -En "^([^|]*\|){52}[^|]*$"
Note the [^|]*$ added at the end. It matches any 0+ chars other than | and then assert the end of line position. So, only lines containing 53 |-separated fields are matched.
Else, you might consider an awk solution (as PS suggests):
awk -F'|' '{if (NF==53) {print NR ":" $0;}}'
where we check for 53 |-separated fields and print the line number, : and the line itself.
