diff deterrmine the difference and display it perhaps in context or as input to an editor

diff - display differences between two files (or directories)

diff [options] old-file new-file

Use - to read from standard input.

diff directory file
Compares the corresponding file in directory . The non-directory file must not be - .

diff directory directory
Compares corresponding files in both directories, in alphabetical order.
This comparison is not recursive unless the -r or ‑‑recursive option is given.

diff never compares the actual contents of a directory as if it were a file. The file that is fully specified may not be standard input, because standard input is nameless and the notion of "file with the same name" does not apply.

Use -- to terminate options when specifing file names which begin with a -.

Multiple single letter options can be combined (example: ‑wyW50)

options to ignore "insignificant" differences
-i
--ignore-case
-B
--ignore-blank-lines Ignore differences that just insert or delete Blank lines.

-b
--ignore-space-change Ignore differences in amount of blanks.

-w
--ignore-all-space Ignore white space when comparing lines.

-I regexp
--ignore-matching-lines= regexp Ignore differences that just insert or delete lines that match regexp.

Option affecting amount of output
-q
--brief quite Do not show differences.
Only whether the files differ, not the details of the differences.
Display "Files old-file and new-file differ" or nothing if the files are the same.
See cmp for "quiter". Check the return code $?
if [ $? -gt 0 ]; then echo -n $'\a ' fi

-t
--expand-tabs to spaces in the output, preserves the alignment of tabs in the input files.

-T
--initial-tab Output a Tab rather than a space before the text of a line in normal or context format, causes the alignment to look normal.

--side-by-side
-y
diff -y dfdf dfdf_1 Avail Mounted Avail Mounted 695M / 695M / 170M /Volumes/DATA 170M /Volumes/DATA 56K /Volumes/BACKUP_2 56K /Volumes/BACKUP_2 919M /Volumes/TBD | 898M /Volumes/TBD xxxx xxxx

-W columns
--width=columns
diff -W70 --side-by-side dfdf dfdf_1 Avail Mounted Avail Mounted 695M / 695M / 170M /Volumes/DATA 170M /Volumes/DATA 56K /Volumes/BACKUP_2 56K /Volumes/BACKUP_2 919M /Volumes/TBD | 898M /Volumes/TBD xxxx xxxx

--suppress-common-lines

diff -wyW$COLUMNS --su dfdf dfdf_1 diff -yW50 --suppress dfdf dfdf_1 919M /Volumes/TBD | 898M /Volumes/TBD

--leftcolumn only
diff -yW60 --left dfdf dfdf_1 Avail Mounted ( 695M / ( 170M /Volumes/DATA ( 56K /Volumes/BACKUP_2 ( 919M /Volumes/TBD | 898M /Volumes/TBD xxxx (

options to ignore "insignificant" differences
`-i` `--ignore-case`
`-B` `--ignore-blank-lines`	Ignore differences that just insert or delete Blank lines.
`-b` `--ignore-space-change`	Ignore differences in amount of blanks.
`-w` `--ignore-all-space`	Ignore white space when comparing lines.
`-I` `regexp` `--ignore-matching-lines=` `regexp`	Ignore differences that just insert or delete lines that match `regexp`.
Option affecting amount of output
`-q` `--brief`	quite Do not show differences. Only whether the files differ, not the details of the differences. Display "`Files old-file and new-file differ`" or nothing if the files are the same. See `cmp` for "quiter". Check the return code `$?` if [ $? -gt 0 ]; then echo -n $'\a ' fi
`-t` `--expand-tabs`	to spaces in the output, preserves the alignment of tabs in the input files.
`-T` `--initial-tab`	Output a Tab rather than a space before the text of a line in normal or context format, causes the alignment to look normal.

When comparing directories:

-s
--report-identical-files Report are identical when files are the same,
otherwise no output is produced.
-x pattern
--exclude=pattern ignore files and subdirectories whose basenames match pattern.

--exclude-from=file ignore files and subdirectories whose basenames match any pattern in file.
-X file ignore files and subdirectories whose basenames match any pattern contained in file.

-r
--recursive compare subdirectories .

-N
--new-file a file found in only in one directory is compared to an empty file.
-P
--unidirectional-new-file a file occuring only in the second directory id compared to an empty file.
-S file
--starting-file=file start with the file file. Use for resuming an aborted comparison.

--horizon-lines=lines Do not discard the last lines lines of the common prefix and the first lines lines of the common suffix.
--from-file= file Compare file to all operands. file can be a directory.

--to-file= file Compare all operands to file. file can be a directory.
-l --paginate Pass the output through pr to paginate it.

-a --text Treat all files as ASCII text and compare them line-by-line, even if they do not seem to be text.

-v
--version

Show the differences with some lines before and after the differences.
  -c Use the context output format
  -C lines
--context=lines. Show lines of context. Default 3.
diff -c dfdf1 dfdf2 *** dfdf1 Tue Sep 5 18:10:15 2006 ← mod date of file prefixed with stars --- dfdf2 Tue Sep 5 18:10:24 2006 *************** ← seperator *** 4,7 **** ← position (column,line) where difference starts in dfdf1 1.3G /Volumes/PHOTOS_1 2.7G /Volumes/PHOTOS_2 56K /Volumes/BACKUP_2 ! 919M /Volumes/TBD ↖ position where difference starts ----4,7 ---- ← position (column,line) where difference starts in dfdf2 1.3G /Volumes/PHOTOS_1 2.7G /Volumes/PHOTOS_2 56K /Volumes/BACKUP_2 ! 898M /Volumes/TBD
  -e
--ed Make output that is a valid ed script.
7c 898M /Volumes/TBD .

  -f
--forward-ed Make output that looks vaguely like an ed script but has changes in the order they appear in the file.
diff -f dfdf dfdf_1 c7 898M /Volumes/TBD .

  -F regexp In context and unified format for each hunk of differences, show some of the last preceding line that matches regexp.
  -n
--rcs Output RCS-format(Revision Control Systems) diffs; like -f except that each command specifies the number of lines affected.

diff -n dfdf dfdf_1 d7 1 a7 1 898M /Volumes/TBD

  -L label
--label=label Use label instead of the file name in the context and unified format headers.

-D name
--ifdef=name Make merged if-then-else format output, conditional on the preprocessor macro name.
--line-format=format Use format to output all input lines in in-then-else format.

%L contents of line %l , excluding any trailing newline
%[-]^*[width][.[prec^*{doxX}^*n printf-style spec for input line number
%% the % character
x the single character x (i.e. any character)
%c'\OOO' the character with octal code OOO

diff --line-format="%8dn %L" dfdf dfdf_1
1 Avail Mounted 2 695M / 3 170M /Volumes/DATA 4 1.3G /Volumes/PHOTOS_1 5 2.7G /Volumes/PHOTOS_2 6 56K /Volumes/BACKUP_2 7 919M /Volumes/TBD 7 898M /Volumes/TBD 8 xxxx

--old-line-format=format... a line taken from just the first file
--new-line-format=format ...a line taken from just the second file
--unchanged-line-format=format ... a line common to both files

% lines from FILE1
%> lines from FILE2
%= lines common to FILE1 and FILE2
%% %
%c'C' the single character C
%c'\OOO' the character with octal code OOO
%[-][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
--changed-group-format=format Use format to output a line group containing differing lines from both files
--old-group-format=format ... the first file
--new-group-format=format ...the second
--unchanged-group-format=format ... of common lines from both files

-u Use the unified output format.
-U lines --unified[=lines] Use the unified output format, showing lines of context. default 3.

#cat 0 Avail Mounted 10632 / 791 /Volumes/DATA 560 /Volumes/PHOTOS 3504 /Volumes/BACKUPS 4542 /Volumes/linux 934 /Volumes/SWAP
#cat 00 Avail Mounted 10639 / 791 /Volumes/DATA 560 /Volumes/PHOTOS 3504 /Volumes/BACKUPS 4542 /Volumes/linux 934 /Volumes/SWAP

diff -u 0 00 --- 0 2007-01-14 21:07:11.000000000 -0500 +++ 00 2007-01-14 21:15:54.000000000 -0500 @@ -1,5 +1,5 @@ Avail Mounted -10632 / +10639 / 791 /Volumes/DATA 560 /Volumes/PHOTOS 3504 /Volumes/BACKUPS

-p
--show-c-function
--show-function-line=regexp In context and unified format, for each hunk of differences, show some of the last preceding line that matches regexp.

--sdiff-merge-assist Print extra information to help sdiff. sdiff uses this option when it runs diff. This option is not intended for users to use directly.

-d --minimal Change the algorithm to perhaps find a smaller set of changes. slower (sometimes much slower).
-H
--speed-large-files Use Heuristics to speed handling of large files that have numerous scattered small changes.

See

cmp , comm, diff3(1), ed(1), patch(1), pr(1), sdiff(1).

DIAGNOSTICS exit status
0 no differences were found, 1 some differences were found, and 2 means trouble ( file not found/accessible,...).

cmp options file1 file2

-b --print-bytes output differing bytes.
file1 file2 differ: byte 1232, line 38 is

164^† t^‡
163^† s^‡

file1

file2

-i SKIP --ignore-initial=SKIP Skip the first SKIP bytes of input.
-i SKIP1:SKIP2 --ignore-initial=SKIP1:SKIP2 Skip the first SKIP1 bytes of FILE1 and the first bytes of FILE2.
-l --verbose Output byte numbers and values of all differing bytes.
-n LIMIT --bytes=LIMIT Compare at most LIMIT bytes.
-s --quiet --silent Output nothing; test the return value
-v --version
--help
Return values: 0 - files are identical; 1 - files differ; 2 - inaccessible or missing argument

comm [OPTION]... FILE1 FILE2
Compare sorted files FILE1 and FILE2 line by line displaying lines in common.
With no options, produce three-column output.
first Column contains lines unique to FILE1,
second column contains lines unique to FILE2 and
last column contains lines common to both files.
-1 suppress lines unique to FILE1 (first column)
-2 suppress lines unique to FILE2 (secondcolumn)
-3 suppress lines that appear in both files (last column)

--help
--version output version information and exit

> cat 1 aaaaaaaaa bbbbbbbb ccccccc > cat 2 aaaaaaaaa b222bbbb ccccccc > comm 1 2 aaaaaaaaa b222bbbb bbbbbbbb ccccccc

diff

When comparing directories:
`-s` `--report-identical-files`	Report are identical when files are the same, otherwise no output is produced.
`-x` `pattern` `--exclude=pattern`	ignore files and subdirectories whose basenames match `pattern`.
`--exclude-from`=`file`	ignore files and subdirectories whose basenames match any pattern in `file`.
`-X` `file`	ignore files and subdirectories whose basenames match any pattern contained in `file`.
`-r` `--recursive`	compare subdirectories .
`-N` `--new-file`	a file found in only in one directory is compared to an empty file.
`-P` `--unidirectional-new-file`	a file occuring only in the second directory id compared to an empty file.
`-S` `file` `--starting-file=file`	start with the `file` file. Use for resuming an aborted comparison.

`--horizon-lines=lines`	Do not discard the last `lines` lines of the common prefix and the first `lines` lines of the common suffix.
`--from-file=` `file`	Compare file to all operands. `file` can be a directory.
`--to-file=` `file`	Compare all operands to file. `file` can be a directory.
`-l` `--paginate`	Pass the output through `pr` to paginate it.
`-a` `--text`	Treat all files as ASCII text and compare them line-by-line, even if they do not seem to be text.
`-v` `--version`