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From GNU less manpage

-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.

This is a great way of searching in GNU less, while ignoring case sensitivity. However, you must know in advance that you'd like to search while ignoring case sensitivity and indicate it in the command line.

vim solves this problem by letting the user specify \c before a search, to indicate that the pattern should be searched while ignoring case sensitivity.

Is there a way to do the same in less (without specifying -I in the command line)?

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  • 4
    You can set the LESS environment variable to "-I" and each time you run less it will get the -I option
    – m_vitaly
    Commented May 24, 2009 at 9:12

2 Answers 2

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You can set it from within less by typing -i and then doing the normal search procedure.
Have a look in the help for less by pressing h

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  • Thanks :) I was looking only at the man page, and forgot to look at the inline help. This is exactly what I was looking for.
    – Tom Feiner
    Commented May 24, 2009 at 11:36
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    FYI, if you add any capital letters to your search, it will run a case-sensitive search even with Ignore Case enabled.
    – MrMas
    Commented Feb 10, 2020 at 23:28
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After turning on Ignore case in searches by pressing -i you'll have to supply a lower case search pattern to perform a case insensitive search. If the search pattern has upper case characters the search will still be case sensitive.

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