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Full Discussion: Question on bash redirection
Top Forums UNIX for Beginners Questions & Answers Question on bash redirection Post 303035997 by MadeInGermany on Wednesday 12th of June 2019 01:51:45 AM
Old 06-12-2019
x < y means: run command x and feed its input (stdin) from file y.
It is true that file y is opened for reading before command x runs.
diff <(sort testfile.txt) <(sort testfile2.txt) means: open a device ("/dev/fd/..."), run sort and redirect its output to the device, open another device, run another sort and redirect its output, run diff with the two devices as arguments (that diff treats as input filenames).
Quote:
man bash
...
Process substitution
...
The process list is run asynchronously, and its input or output appears as a filename. This filename is passed as an argument to the current command as the result of the expansion. If the >(list) form is used, writing to the file will provide input for list. If the <(list) form is used, the file passed as an argument should be read to obtain the output of list. Note that no space may appear between the < or > and the left parenthesis, otherwise the construct would be interpreted as a redirection. Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files.
...
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LEARN ABOUT LINUX

git-difftool

GIT-DIFFTOOL(1) 						    Git Manual							   GIT-DIFFTOOL(1)

NAME

       git-difftool - Show changes using common diff tools

SYNOPSIS

       git difftool [<options>] [<commit> [<commit>]] [--] [<path>...]

DESCRIPTION

       git difftool is a Git command that allows you to compare and edit files between revisions using common diff tools. git difftool is a
       frontend to git diff and accepts the same options and arguments. See git-diff(1).

OPTIONS

       -d, --dir-diff
	   Copy the modified files to a temporary location and perform a directory diff on them. This mode never prompts before launching the diff
	   tool.

       -y, --no-prompt
	   Do not prompt before launching a diff tool.

       --prompt
	   Prompt before each invocation of the diff tool. This is the default behaviour; the option is provided to override any configuration
	   settings.

       -t <tool>, --tool=<tool>
	   Use the diff tool specified by <tool>. Valid values include emerge, kompare, meld, and vimdiff. Run git difftool --tool-help for the
	   list of valid <tool> settings.

	   If a diff tool is not specified, git difftool will use the configuration variable diff.tool. If the configuration variable diff.tool is
	   not set, git difftool will pick a suitable default.

	   You can explicitly provide a full path to the tool by setting the configuration variable difftool.<tool>.path. For example, you can
	   configure the absolute path to kdiff3 by setting difftool.kdiff3.path. Otherwise, git difftool assumes the tool is available in PATH.

	   Instead of running one of the known diff tools, git difftool can be customized to run an alternative program by specifying the command
	   line to invoke in a configuration variable difftool.<tool>.cmd.

	   When git difftool is invoked with this tool (either through the -t or --tool option or the diff.tool configuration variable) the
	   configured command line will be invoked with the following variables available: $LOCAL is set to the name of the temporary file
	   containing the contents of the diff pre-image and $REMOTE is set to the name of the temporary file containing the contents of the diff
	   post-image.	$MERGED is the name of the file which is being compared.  $BASE is provided for compatibility with custom merge tool
	   commands and has the same value as $MERGED.

       --tool-help
	   Print a list of diff tools that may be used with --tool.

       --[no-]symlinks

	   git difftool's default behavior is create symlinks to the working tree when run in --dir-diff mode and the right-hand side of the
	   comparison yields the same content as the file in the working tree.

	   Specifying --no-symlinks instructs git difftool to create copies instead.  --no-symlinks is the default on Windows.

       -x <command>, --extcmd=<command>
	   Specify a custom command for viewing diffs.	git-difftool ignores the configured defaults and runs $command $LOCAL $REMOTE when this
	   option is specified. Additionally, $BASE is set in the environment.

       -g, --gui
	   When git-difftool is invoked with the -g or --gui option the default diff tool will be read from the configured diff.guitool variable
	   instead of diff.tool.

       See git-diff(1) for the full list of supported options.

CONFIG VARIABLES

       git difftool falls back to git mergetool config variables when the difftool equivalents have not been defined.

       diff.tool
	   The default diff tool to use.

       diff.guitool
	   The default diff tool to use when --gui is specified.

       difftool.<tool>.path
	   Override the path for the given tool. This is useful in case your tool is not in the PATH.

       difftool.<tool>.cmd
	   Specify the command to invoke the specified diff tool.

	   See the --tool=<tool> option above for more details.

       difftool.prompt
	   Prompt before each invocation of the diff tool.

SEE ALSO

       git-diff(1)
	   Show changes between commits, commit and working tree, etc

       git-mergetool(1)
	   Run merge conflict resolution tools to resolve merge conflicts

       git-config(1)
	   Get and set repository or global options

GIT

       Part of the git(1) suite

Git 1.8.5.3							    01/14/2014							   GIT-DIFFTOOL(1)
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