Linux diff Command
Learn Linux div Command with examples
Published
- Linux diff Command
- diff command Syntax
- diff command Example
- diff -c Produce Output in the Context Format
- diff -u Produce Output in the Unified Format
- diff -i Command Tells to Ignores Case
- diff Command in Linux (Documentation)
Linux diff Command
In Linux we can use “diff” command to display the differences in the files by comparing the files line by line. diff stands for difference.
Note: diff command uses certain special symbols and instructions that are required to make two files identical.
diff command Syntax
>> diff [options] File1 File2
Let’s create two files. fruits_1.txt and fruits_2.txt
The following comand will create fruits_1.txt file.
>> echo -e "Apple\nCherry\ngrapes\nMango\nKiwi\nstrawberry\nWatermelon" > fruits_1.txt
# File created with content
Apple
Cherry
grapes
Mango
Kiwi
strawberry
Watermelon
The following comand will create fruits_2.txt file.
>> echo -e "Apple\nApricot\nCherry\ngrapes\nLychee\nKiwi\nWatermelon" > fruits_2.txt
# File created with content
Apple
apricot
Cherry
grapes
Lychee
Kiwi
Watermelon
Basic diff command is run on two text files without any option, it will produces an output in the normal format.
diff command Example
>> diff file_1.txt file_2.txt
1a2
> apricot
4c5
< Mango
---
> Lychee
6d6
< strawberry
1a2, 4c5 and 6d6 are the part of diff command output of our files fruits_1.txt and fruits_2.txt that has specific meaning to understand.
Each change command contains the following, from left to right.
- The line number or range of lines in the first file like fruits_1.txt.
- A special change character like a, c or d.
- The line number or range of lines in the second file like fruits_2.txt.
| Special Symbol | Description |
| a | add |
| c | change |
| d | delete |
- 1a2 - Add line 2 of the second file at the beginning of the file1 (after the line 1).
- apricot - The line from the second line that is added to the first file as described above.
- 4c5 - Replace (change) line 4 in the first file (Mango) with lines 4-5 (Lychee) from the second file.
- 6d6 - Delete line 6 (strawberry) in the first file . The 6 after the d symbol means that if the line is not deleted it would appear on line 6 (strawberry) in the second file.
The output starts with the names and the timestamps of the files that are compared, and one or more sections that describe the differences.
Lines starting with two spaces are lines of context, the lines that are the same in both files.
- + Plus symbol (+) are the lines that shows that the lines missing in the first file.
- + Minus symbol (-) are the lines that shows that the lines missing in the second file.
- ! Exclamation Mark symbol (!) are the lines that shows that the changed between two files. Each group of lines starting with ! from the first file has a corresponding match in the second file.
diff -c Produce Output in the Context Format
>> diff -c fruits.txt fruits2.txt
*** fruits_1.txt 2022-05-10 12:28:22.847819700 +0500
--- fruits_2.txt 2022-05-10 12:27:31.137819700 +0500
***************
*** 1,7 ****
Apple
Cherry
grapes
! Mango
Kiwi
- strawberry
Watermelon
--- 1,7 ----
Apple
+ apricot
Cherry
grapes
! Lychee
Kiwi
Watermelon
diff -u Produce Output in the Unified Format
>> diff -u fruits.txt fruits2.txt
--- fruits.txt 2022-05-10 12:28:22.847819700 +0500
+++ fruits2.txt 2022-05-10 12:27:31.137819700 +0500
@@ -1,7 +1,7 @@
Apple
+apricot
Cherry
grapes
-Mango
+Lychee
Kiwi
-strawberry
Watermelon
The output begins with the names and the timestamps of the files and one or more sections that describe the differences.
diff -i Command Tells to Ignores Case
>> diff -ci fruits.txt fruits2.txt
*** fruits.txt 2022-05-10 12:28:22.847819700 +0500
--- fruits2.txt 2022-05-10 12:27:31.137819700 +0500
***************
*** 1,7 ****
Apple
Cherry
grapes
! Mango
Kiwi
- strawberry
Watermelon
--- 1,7 ----
Apple
+ apricot
Cherry
grapes
! Lychee
Kiwi
Watermelon
The diff command compares files line by line.
Comparing text files for differences is one of the most common tasks for administrators when updating/copying files.
diff Command in Linux (Documentation)
~$ man diff
NAME
GNU diff - compare files line by line
SYNOPSIS
diff [OPTION]... FILES
DESCRIPTION
Compare FILES line by line.
Mandatory arguments to long options are mandatory for short options
too.
--normal
output a normal diff (the default)
-q, --brief
report only when files differ
-s, --report-identical-files
report when two files are the same
-c, -C NUM, --context[=NUM]
output NUM (default 3) lines of copied context
-u, -U NUM, --unified[=NUM]
-e, --ed
output an ed script
-n, --rcs
output an RCS format diff
-y, --side-by-side
output in two columns
-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
-r, --recursive
recursively compare any subdirectories found
--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
-Z, --ignore-trailing-space
ignore white space at line end
-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
format LTYPE input lines with 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)
-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
FILES are 'FILE1 FILE2' or 'DIR1 DIR2' or 'DIR FILE' or 'FILE DIR'.
If --from-file or --to-file is given, there are no restrictions on
FILE(s). If a FILE is '-', read standard input. Exit status is 0 if
inputs are the same, 1 if different, 2 if trouble.