Shell command: diff

Command line options

Some interesting options, IHMO, include

`-y`	Side by side (output is shown in two columns). Long option is `--side-by-side`.
`-Z`	Ignore trailing whitespace. This is useful if diffing files that have been saved in Unix and Windows because of their differing end of line bytes. Long options `--ignore-trailing-space`
`-q`	Report only if file differs. This is especially useful when used in conjunction with `-r`. Long option is `--brief`
`-r`	Compare a directory tree, rather than a single file. I like to combine `-r` with `-q` so that I simply see which files have changed or were added (or deleted). Long option is `--recursive`

Other options are

	`--normal`		output a normal diff (the default)
`-s`	`--report-identical-files`		report when two files are the same
`-c`, `-C`	`--context`	`[NUM]`	output `NUM` (default 3) lines of copied context
`-u`, `-U`	`--unified`	`[NUM]`	output `NUM` (default 3) lines of unified context
`-e`	`--ed`		output an ed script
`-n`	`--rcs`		output an RCS format diff
`-W`	`--width=NUM`		output at most NUM (default 130) print columns
	`--left-column`		output only the left column of common lines
	`--suppress-common-lines`		do not output common lines
`-p`	`--show-c-function`		show which C function each change is in
`-F`	`--show-function-line=`	`RE`	show the most recent line matching `RE`
	`--label`	`LABEL`	use `LABEL` instead of file name and timestamp (can be repeated)
`-t`	`--expand-tabs`		expand tabs to spaces in output
`-T`	`--initial-tab`		make tabs line up by prepending a tab
	`--tabsize=`	`NUM`	tab stops every `NUM` (default 8) print columns
	`--suppress-blank-empty`		suppress space or tab before empty output lines
`-l`	`--paginate`		pass output through 'pr' to paginate it
	`--no-dereference`		don't follow symbolic links
`-N`	`--new-file`		treat absent files as empty
	`--unidirectional-new-file`		treat absent first files as empty
	`--ignore-file-name-case`		ignore case when comparing file names
	`--no-ignore-file-name-case`		consider case when comparing file names
`-x`	`--exclude=PAT`		exclude files that match PAT
`-X`	`--exclude-from=`	`FILE`	exclude files that match any pattern in `FILE`
`-S`	`--starting-file=FILE`		start with FILE when comparing directories
	`--from-file=`	`FILE1`	compare FILE1 to all operands; `FILE1` can be a directory
	`--to-file=`	`FILE2`	compare all operands to FILE2; FILE2 can be a directory
`-i`	`--ignore-case`		ignore case differences in file contents
`-E`	`--ignore-tab-expansion`		ignore changes due to tab expansion
`-b`	`--ignore-space-change`		ignore changes in the amount of white space
`-w`	`--ignore-all-space`		ignore all white space
`-B`	`--ignore-blank-lines`		ignore changes where lines are all blank
`-I`	`--ignore-matching-lines=`	`RE`	ignore changes where all lines match `RE`
`-a`	`--text`		treat all files as text
	`--strip-trailing-cr`		strip trailing carriage return on input
`-D`	`--ifdef=NAME`		output merged file with '#ifdef NAME' diffs
	`--GTYPE-group-format=`	`GFMT`	format `GTYPE` input groups with `GFMT`
	`--line-format=`	`LFMT`	format all input lines with `LFMT`
	`--LTYPE-line-format=`	`LFMT`
`-d`	`--minimal`		try hard to find a smaller set of changes
	`--horizon-lines=`	`NUM`	keep `NUM` lines of the common prefix and suffix
	`--speed-large-files`		assume large files and many scattered small changes
	`--color=`	`[WHEN]`	colorize the output; `WHEN` can be `never`, `always` or `auto` (the default)
	`--palette=`	`PALETTE`	the colors to use when `--color` is active; `PALETTE` is a colon-separated list of terminfo capabilities
	`--help`		display this help and exit
`-v`	`--version`		output version information and exit

LTYPE format (LFMT)

These format options provide fine-grained control over the output of diff, generalizing -D/--ifdef.

LTYPE is old, new or unchanged.

GTYPE is LTYPE or 'changed'.

GFMT (only) may contain:

`%<`	lines from FILE1
`%>`	lines from FILE2
`%=`	lines common to FILE1 and FILE2
`%[-][WIDTH][.[PREC]]{doxX}LETTER`	printf-style spec for LETTER

LETTERs are as follows for new group, lower case for old group:

`F`	first line number
`L`	last line number
`N`	number of lines = L-F+1
`E`	F-1
`M`	L+1

%(A=B?T:E) if A equals B then T else E

LFMT (only) may contain:

`%L`	contents of line
`%l`	contents of line, excluding any trailing newline
`%[-][WIDTH][.[PREC]]{doxX}n`	printf-style spec for input line number

Both GFMT and LFMT may contain:

`%%`	%
`%c'C'`	the single character C
`%c'\OOO'`	the character with octal code OOO
`C`	the character C (other characters represent themselves)

Comparing the output of two programs

Process substitution allows to compare the output of two programs. The following example compares the directory and file names in two directories:

$ diff <( ls -1 ~/dir-one )  <( ls -1 ~/dir-two )

Coloring differences

The --color=always option causes the output to be colored in red (deleted lines) and green (added lines).

Unfortunately, it does not work with the -y option.

git diff is similar to using diff --color=always, yet it allows to add --word-diff to highlight changes on one line.

colordiff is a Perl script that colors the output of diff.

diff.exe on Windows

Unfortunately, it seems there is no diff.exe on Windows, by default.

However, when Git is installed, there is also a diff whose path can be set in PowerShell like so. The first line must be used if only one git executable is found in the path, the second one if multiple are found:

$env:path = "$( split-path (where.exe git)   )\..\usr\bin;$env:path"
$env:path = "$( split-path (where.exe git)[0])\..\usr\bin;$env:path"

Because diff is also an alias for compare-object, the diff executable must be explicitly invoked with the .exe suffix. Thus, this alias should (probably) be deleted:

remove-item alias:diff -force