line return in grep search?

Question

I have some files with the text:

xxxxx
xxxxx
<cert>
</cert>
some other stuff

How can I search with grep and ignore the line returns? I have many files in the same folder. I have tried this but it does not seem to stop running:

tr '\n' ' ' | grep '<cert></cert>' *

Answer 1

That is searching for a multi-line pattern, which the usual grep does not appear to support. There are alternative tools, e.g.,

• How can I search for a multiline pattern in a file?, which suggests pcregrep, or custom awk, perl scripts.
• How can I “grep” patterns across multiple lines?, again suggesting pcregrep (as well as sed scripts).

However, GNU grep is said to support this as well:

• How do I grep for multiple patterns on multiple lines? gives as an example

  grep -Pzo "^begin\$(.|\n)*^end$" file

to use a newline in a pattern. The options used however include the "experimental" -P which may make it less suitable than pcregrep:

-P, --perl-regexp

Interpret PATTERN as a Perl regular expression. This is highly experimental and grep -P may warn of unimplemented features.

-z, --null-data

Treat the input as a set of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline. Like the -Z or --null option, this option can be used with commands like sort -z to process arbitrary file names.

-o, --only-matching

Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line.

Some experimental options are useful, others less so. This one was noted as the source of problems in Searching for non-ascii characters.