Filter --help command?

Question

Sometimes I want to search/filter help for particular commands for keywords.

history --help

gives list of options, sometimes it's overwhelming how much info is there. Can I filter it for keywork "clear" e.g.

history --help *clear*

Also sometimes I want all info from --help, but it's so long that some of the lines get lost and I cannot scroll up for them. How can I make it show screen by screen e.g. fill first screen then on key press fill second screen etc.

Question same for file listing command.

Answer 1

--help is not a universal command (it's an argument to the command being called, and has to be provided explicitly by it), so there is no universal solution (in fact, history has no --help option on my system). You probably want something like history --help 2>&1 | grep -E '(^|[^[:alnum:]])clear' (the redirection is necessary for some commands that print their help/usage text on STDERR.

You could make this into a function like so:

helpgrep() {
    [ "$#" -eq 2 ] || return 1
    "$1" --help 2>&1 | grep -E "(^|[^[:alnum:]])$2"
}

Then run it with helpgrep command search-string.

As for your second issue, try piping it to less (or more if less is not available), for example, history --help | less.

Answer 2

To view the commands that have clear in them you could use grep:

history | grep clear

If the output is long you can view it on a page-page basis using pipe the output thru more:

 history | more

Of course you can combine these

history | grep clear | more

This is not specific to just history so can be applied to any other command where you want to filter results and/or view ouptut a screen height at a time.

Answer 3

history --help | grep clear shows you the lines that contain the word (or part of a word) clear. This is a pipeline, where the output of the first command (history --help) becomes the input of the second command (grep clear, and grep is a command to search for a pattern in some text). You can also browse the whole help by running history --help | less (less is a text file viewer) and use the / key in less to search for clear.