How do you do a case insensitive search using a pattern modifier using less?

Question

It seems like the only way to do this is to pass the -i parameter in when you initially run less. Does anyone know of some secret hack to make something like this work

/something to search for/i

Uird

Answer 1

You can also type command -I while less is running. It toggles case sensitivity for searches.

Protochordate

-i means ignore case in searches that do not contain uppercase while -I ignores case in all searches. – Koblenz

"ignore case in searches that do not contain uppercase" is called "smart case" in vim and ack. Adding this here for googlability. – Elburr

@HelloGoodbye you don't "run a command" just type it, I was confused by the phrasing as well. – Fasano

-I as in literally type -I with less open. – Overspread

Answer 2

You can also set the environment variable LESS

I use LESS=-Ri, so that I can pump colorized output from grep into it, and maintain the ANSI colour sequences.

Another little used feature of less that I found is starting it with +F as an argument (or hitting SHIFT+F while in less). This causes it to follow the file you've opened, in the same way that tail -f <file> will. Very handy if you're watching log files from an application, and are likely to want to page back up (if it's generating 100's of lines of logging every second, for instance).

Rationalize

Following with less is SO much more useful than with tail. Especially logs with a lot of action. – Digitalism

@Digitalism You could say less is more :) – Mercantile

@MartinKonecny less may be more, but less is not more let alone most – Rationalize

@Rationalize I didn't know most, tried it and sidescroll is really cool, thanks – Jeramie

I would use less +F --follow-name some.file. +F alone not working for me. – Floro

less is more than more, most is more than less | less is more, but more more than more is, so more is less less, so use more less if you want less more. – Adina

While this works when you start less yourself, for things like hg log or git stuff that use less, this unfortunately doesn't work for me. Luckily remembering -I once less is running isn't too bad. – Cyme

Answer 3

Add-on to what @Juha said: Actually -i turns on Case-insensitive with SmartCasing, i.e if your search contains an uppercase letter, then the search will be case-sensitive, otherwise, it will be case-insensitive. Think of it as :set smartcase in Vim.

E.g.: with -i, a search for 'log' in 'Log,..' will match, whereas 'Log' in 'log,..' will not match.

Siriasis

Actually, if any letter, not just the first one, is uppercase the search will be case sensitivite. An important difference (and indicentally how I prefer it to be). This is also how vim's smartcase works. – Burkhart

In Vim you can also say /\clog to switch to case-insensitive search. – Eating

Answer 4

It appears that you can summon this feature on a per search basis like so:

less prompt> /search string/-i

This option is in less's interactive help which you access via h:

less prompt> h
...
  -i  ........  --ignore-case
                  Ignore case in searches that do not contain uppercase.
  -I  ........  --IGNORE-CASE
                  Ignore case in all searches.
...

I've not extensively checked but the help in less version 487 on MacOS as well as other Linux distros lists this option as being available.

On MacOS you can also install a newer version of less via brew:

$ brew install less
$ less --version
less 530 (POSIX regular expressions)
Copyright (C) 1984-2017  Mark Nudelman

References

• less is always case-insensitive

Artina

@IlikeSerena - it may be an issue w/ specific versions of less. – Artina

@Artina which less did you try this on ? Doen't work on my less 458 (GNU regular expressions) (aptitude says less 458-2 FWIW) – Signification

@Signification - I do not have access to the system currently but was on whatever version of less that's included w/ Fedora 19/20. – Artina

@Artina Thanks, probably a more recent release than 458-2, such as 458-6 as this particular one was built for Fedora on 2014-02-10 according to koji.fedoraproject.org/koji/packageinfo?packageID=759 and since you posted this on Feb 22 '14... – Signification

Doesn't work on mac with less 487 (POSIX regular expressions) – Adina

@SumitJain - you could try installing newer version of less on MacOS, see updates. NOTE: that the -i switch is listed in version 487's help. – Artina

This doesn't work with less 590 (GNU regular expressions) in Ubuntu – Waller

Answer 5

When using -i flag, be sure to enter the search string completely in lower case, because if any letter is upper case, then its an exact match.

See also: the -I (capital i) flag of less(1) to change this behavior.

Chowchow