Where is less search pattern reference?

Question

Where can I find reference for less regex search patterns?

I want to search file with less using \d to find digits, but it does not seem to understand this wildcard. I tried to find a reference for less regex patterns, but could not find anything, not on man pages and not on the Internet.

score 33 · Accepted Answer · answered Jul 03 '18 at 14:31

33

less's man page says:

   /pattern
          Search forward in the file for the N-th line containing
          the pattern.  N defaults to 1.  The pattern is a regular
          expression, as recognized by the regular expression library
          supplied by your system.

so the accepted syntax may depend on your system. Off-hand, it seems to accept extended regular expressions on my Debian system, see regex(7), and Why does my regular expression work in X but not in Y?

\d is from Perl, and isn't supported by all regex engines. Use [0-9] or [[:digit:]] to match digits. (Their exact behaviour may depend on the locale.)

answered Jul 03 '18 at 14:31

ilkkachu

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> *as recognized by the regular expression library supplied by your system.* < so… any way to direct `less` to `libpcre`? – JamesTheAwesomeDude Jan 28 '21 at 20:54
I have Debian 10 according to lsb_release. If I run less on a file that contains a's and e's, and use the command `/a|e/`, less only highlights the a's. If I enter the command `/a\|e/` I get pattern not found. This tends to support that less is accepting the basic syntax, according to `man re_format`. If I made a mistake in trying to invoke extended syntax, please let me know. – cardiff space man Jun 09 '22 at 22:51
@cardiffspaceman, did you put the trailing `/` there? I don't think `less` expects that, so it'll look for the string `e/` as the other alternative. It has to be extended regexes, since BRE doesn't have the alternation, and in BRE, `a|e` would look for that literal string – ilkkachu Jun 09 '22 at 23:02
@likkachu leaving off the trailing `/` does make the command work as expected, extended RE. – cardiff space man Jun 15 '22 at 01:09

Kusalananda · Answer 2 · 2019-06-18T13:22:07.550

The expressions supported by less are documented in the re_format(7) manual (man 7 re_format). That manual describes both the extended regular expressions and the basic regular expressions available on your system. The less utility understands extended regular expressions.

To match a digit, you would use [0-9] or [[:digit:]] (there's a slight difference as the former depends on the current locale). The \d pattern is a Perl-like regular expression (PCRE), not supported by less.

Where is less search pattern reference?

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