less searches are always case-insensitive

Question

Trying to find out how to use case-insensitive searches in less I found this on serverfault.

That seems to perfectly answer my question. The problem is: It doesn't work like that here (OpenSUSE 13.1; less 458).

I had aliased less to less -WiNS but I changed that. But even calling it as command less file does not change anything. I have checked with ps that there is no -i option in the command line any more.

As the answer says the less help (pressing h) states that I can use -i within less, too. If I use that once then less tells me it had changed to case-insensitive search (that is kind of correct: nothing changes). If I use it twice then less tells me it had turned to case-sensitive search. And right, then it works as it should from the start. Giving -i twice on the command line does not work, though.

What's up here?

Answer 1

I'm not sure how to enable this from the command line but when you're inside of less you can toggle the behavior you want by giving the -i command to less.

toggling -i

              

searching for /blah and /BLAH

             

searching for /Blah

      

Apparently you can also summon this mode on demand by suffixing your searches with a -i.

Example

less prompt> /search string/-i

References

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

Answer 2

You can start less and ignore case by passing the -i option. This ignores case unless the search string has an upper-case character. Here is the summary on less from the Ubuntu help page:

   -i or --ignore-case
          Causes searches to ignore case; that is, uppercase  and  lowercase  are  considered
          identical.   This  option  is ignored if any uppercase letters appear in the search
          pattern; in other words, if a pattern contains uppercase letters, then that  search
          does not ignore case.

   -I or --IGNORE-CASE
          Like -i, but searches ignore case even if the pattern contains uppercase letters.

Other versions of less may vary in their interpretations of -i.

Answer 3

The manual (for my less, version 444) says:

      Options are also taken from the environment variable "LESS".  For exam‐
   ple, to avoid typing "less -options ..." each time less is invoked, you
   might tell csh:

   setenv LESS "-options"

   or if you use sh:

   LESS="-options"; export LESS

   On  MS-DOS,  you don't need the quotes, but you should replace any per‐
   cent signs in the options string by double percent signs.

   The environment variable is parsed before the command line, so  command
   line  options  override  the  LESS  environment variable.
       On  MS-DOS,  you don't need the quotes, but you should replace any per‐
   cent signs in the options string by double percent signs.

   The environment variable is parsed before the command line, so  command
   line  options  override  the  LESS  environment variable.  If an option
   appears in the LESS variable, it can be reset to its default  value  on
   the command line by beginning the command line option with "-+".

So, I would check if the environment variable LESS might be set somewhere, in your shell "dot files" perhaps. Also, less -+i should reset the -i to its default (which is case-sensitive). If that brings back the case-sensitivity for you, then you could just alias less=less -+i, maybe together with alias lessi=less -i.

Answer 4

Quick guide in 2 steps: Do your search:

:/put search lowercase word here after slash

Then after all the case sensitive matches are highlighted:

:-i

This will highlight all matches regardless of case.

Answer 5

You can pass parameter to the less command when you open your file, and all your searches will be case insensitive.

$ less -i <file_name>

or you can modify your .bashrc file so it your less will always be case-insensitive

export LESS="-i"

Answer 6

For what it's worth, I had something of the opposite problem: on the system I was working on, searches within less were always case insensitive. After some investigation, I discovered that the $LESS shell environment variable was being set to a default value, which included the -I flag. I was able to override the defaults by setting it within my user shell setting (~/.bashrc).

If you are experiencing something similar (with less behaving differently to what you would expect without explicitly directing it to run in case-insenstive mode, for example), you could try running env | grep LESS.