Add Configure File Support - Version 2

[decaff]

Implementation is based on PR #257, authored by David Schlosnagle.

Ag reads OPTIONS from one of several configuration files. Ag processes "config
file" options before command-line options. The config file format is very
simple:

# this is a comment => inline comments not supported
# blank lines okay as well

--long-option[=value]
-short-option[=value]
--long-option[ value]
-short-option[ value]

# And special keywords (of which there is only one)
list

    Actual Example Config File
    ==========================
    # set up nice colors for a white terminal bkgnd...

    # bold blue
    --color-line-number=1;34
    # black with grey bkgnd
    --color-match=30;47
    # green
    --color-path=32

If the keyword "list" is included in a config file, ag dumps the contents of
argv[] on stdout. This is useful for debugging config file errors that cause
ag to output a usage message and then silently exit.

Ag reads configuration information from a number of possible locations,
in the following order (first file found is used, all others ignored):

1.   Path specified in $AGRC_PATH
2.   $XDG_CONFIG_HOME/agrc
3.   ~/.agrc
4.   /usr/local/etc/agrc
5.   /etc/agrc

[aisapatino]

@ggreer thoughts on this? or some other way of supporting default options? #574

[deivid-rodriguez]

@ggreer Are you considering this?

[vampolo]

@ggreer fell on this today. any chance it will be merged?

[rosshadden]

👍 This would be a lot better than aliasing ag to ag --with --various --options.

[lgarron]

I would also love to see a defaults file. I have had trouble switching to ag instead of grep because I kept missing results – I just found out today I should always pass in the --hidden flag to help with that (and then use .agignore to exclude.git dirs).

For what it's worth, I got here via (!):

1. Google search for "the_silver_searcher default arguments" (second result)
2. Environment variable for default parameters #79 ("Actually, I've changed my mind about this feature. It really seems like aliases are the way to go.")
3. support for AG_OPTIONS #121
4. Add support for ~/.agrc default config options #257
5. Ag config file support implemented #701

It would be nice if the file could be located either at ~/.agrc or under ~/.config/, as git and many other tools allow. But I guess .agignore doesn't support that either, and any control would be better than none.

As a user of fish, I try not to implement default argument handling in my shell configuration itself. A configuration file is more consistent with all my other shell tools.

[kugel-]

@ggreer please consider this. I'm coming from ack and truly miss this.

[stfl]

+1

[ZyX-I]

I would say that current PR has some flaws:

1. ~/.agrc should not be present present at all: XDG spec does not expect this.
2. Yet I would suggest to use ./.agrc, ../.argrc, ../../.agrc, etc; in many cases this would also pickup ~/.agrc.
3. Need a command-line option to ignore agrc files completely. Alternatively: command-line option to specify one agrc file which will be used in place of all defaults, AGRC_PATH is not needed much in this case.
4. System-wide configuration should be using ${XDG_CONFIG_DIRS:-/etc/xdg}, $xdg_config_dir/agrc (XDG_CONFIG_DIRS is a list): XDG spec also cares about this.

[jxpx777]

I would strongly suggest this not be put directly into the XDG_CONFIG_HOME. Instead, I would suggest using a subdirectory of XDG_CONFIG_HOME the same way git and others do: $XDG_CONFIG_HOME/ag/agrc. It's been suggested in #1020 that the ignore lookup should also conform to XDG spec, and having these all in a single directory makes more sense than proliferating directly in the root of $XDG_CONFIG_HOME