Is there a shortcut for word boundary in `less`?

Question

This is the less I am using:

less 458 (POSIX regular expressions)
Copyright (C) 1984-2012 Mark Nudelman

In Vim it is \< and \>, in most other regex it is \b.

What's the output of `ldd /usr/bin/less` (presupposing that's the correct path)? — tripleee, Mar 30 '14 at 11:18

score 25 · Answer 1 · edited May 23 '17 at 10:31

25

The character classes [[:<:]] and [[:>:]] match beginning and end of word, respectively, in system less on OS X 10.11.5. I haven't found a way to make the documented short forms \<, \>, or \b work.

(Thanks to denis for the suggestion to check man 7 re_format.)

edited May 23 '17 at 10:31

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answered May 30 '16 at 22:19

Jack Foy

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Ridiculously convoluted solution. Yet again Mac OS behavior is different from everywhere else. – Spidey Oct 19 '21 at 12:57

janos · Accepted Answer · 2014-03-30T14:31:41.383

Your version of less was built with posix regular expressions, as if:

wget http://ftp.gnu.org/gnu/less/less-451.tar.gz
tar zxf less-451.tar.gz
cd less-451
./configure --with-regex=posix
make

However, apparently the cause of whether \< works or not does NOT depend on this:

In Debian/Linux, \< will work fine even if you build with the above commands, with posix regex
In Mac OS X, I tried all possible values of --with-regex except pcre, and \< doesn't work with any of them. If I build with pcre, then \b works, instead of \<.

To conclude, I don't know how to make it work with \<. But you can build yourself with pcre and then it should work with \b. If you are not a sysadmin, you probably want to use a --prefix to install under your home directory, for example --prefix=$HOME/opt. After the make step, confirm it works with ./less /path/to/some/file. If looks good, then finish with make install.

On MacOS with `homebrew`: `brew install less --with-pcre` will automatically compile less with PCRE-regular-expressions capabilities. — Stefan van den Akker, Nov 16 '17 at 10:13

denis · Answer 3 · 2015-09-06T09:04:29.293

First see if man 7 re_format on your computer has an "Enhanced features" section which lists \< etc. If it does, change one line in less-451/pattern.h:

#define REGCOMP_FLAG  REG_ENHANCED  // not REG_EXTENDED

Then ./configure --with-regex=posix; make less will understand \< .

This works on Macosx 10.8; on other systems, try following /usr/include/regex.h .
(Gnu.org has a round dozen Regular-expression-syntaxes ?! )

jlliagre · Answer 4 · 2014-03-30T09:02:48.470

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less generally uses vi syntax, i.e. \< and \> unless it has been compiled with the --with-regex=none configure option or if the regular expression library found at compilation time doesn't provide word boundary search. Your system might also provide a different syntax.

edited Mar 30 '14 at 09:02

answered Mar 30 '14 at 08:13

jlliagre

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Answer updated, you should tell what OS your are using as the behavior is platform dependent. – jlliagre Mar 30 '14 at 09:03

score 0 · Answer 5 · answered Mar 24 '23 at 20:15

On my macOS v12.6.3 system, the following enables vim-like, \b word-boundary-searching:

brew install less
echo PAGER='less'
hash -r # in bash, to discover new, homebrew-based less(1) path

Also, fyi:

$ less --version | head -2
less 608 (PCRE2 regular expressions)
Copyright (C) 1984-2022  Mark Nudelman
$

More, related details about my test system: https://gist.githubusercontent.com/johnnyutahh/0ca86ec252f832cfc512eaf56acecc3c/raw

Is there a shortcut for word boundary in `less`?

5 Answers5

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