Editing Comparing files

== Comparison script ==

The script below takes two arguments on the command-line and compares them via <code>[https://en.wikipedia.org/wiki/Diff diff]</code> command. It also echoes generic human-readable answer saying whether two file system objects are equal. As <code>diff</code> compares directories as well as files, paths to directories are valid arguments as well.

<source lang="bash">
#!/bin/bash

if [ $# != 2 ] ; then
    echo 'Expected exactly two arguments'
    exit 1
fi

if [ -f "$1" -a -f "$2" ]; then
    : # OK, do nothing here
elif [ -d "$1" -a -d "$2" ]; then
    : # OK, do nothing here
else
    if [ -f "$1" ]; then
        type_of_1='file'
    else
        type_of_1='directory'
    fi
    if [ -f "$2" ]; then
        type_of_2='file'
    else
        type_of_2='directory'
    fi
    echo "Arguments are of different type ($type_of_1/$type_of_2)"
    exit 1
fi

if diff "$1" "$2" > /dev/null 2>&1; then
    echo 'Equal'
else
    echo 'Not equal'
fi
</source>

== Plugging the script into vifm ==

To use it in Vifm:

# Save the script as <code>compare-cmd</code> (not <code>[https://en.wikipedia.org/wiki/Cmp_(Unix) cmp]</code> or <code>[http://linux.die.net/man/1/compare compare]</code> to avoid name conflict with existing tools) at one of directories listed in your <code>[https://en.wikipedia.org/wiki/PATH_(variable) $PATH]</code> environment variable or under <code>$VIFM/scripts</code> (most likely that it's <code>~/.vifm/scripts</code>).
# On Unix-like operating systems make the script file executable by running<br><code>[https://en.wikipedia.org/wiki/Chmod chmod] +x compare-cmp</code>
# Add following lines to your <code>vifmrc</code>:<code>
    command! cmpinternal compare-cmd %a %S
    command! cmp : if expand('%%c') == expand('%%f')
               \ |     echo expand('Comparing %%"c and %%"C:t ...')
               \ |     cmpinternal %c %C
               \ | else
               \ |     echo expand('Comparing files: %%"f ...')
               \ |     cmpinternal %f
               \ | endif
</code>

Explanation of key parts:
* <code>cmpinternal</code> — a trick to invoke external command. Calling <code>execute "!compare-cmd ... %S"</code> reparses command-line which leads to loosing results of command execution (they are overwritten by execution of <code>if-else-endif</code> block).
* Double percent sign in arguments for the <code>expand()</code> function (e.g. <code>expand('%%c')</code>) — macros are automatically expanded for user-defined commands, so <code>%</code> symbol should be escaped with itself for expansion to be performed by <code>expand()</code> function. It's important as otherwise unescaped quotes or other special characters in file names can break command syntax.
* <code>expand('%%c') == expand('%%f')</code> — check whether only one file is selected in current pane.

== Usage ==

* Run <code>:cmp</code> without selection or with single file selection to compare files under cursors in two panes.
* Run <code>:cmp</code> after selecting two files in the current pane to compare them.

Results are printed on the status bar (because of <code>%S</code> macro in <code>cmdinternal</code>).