How do I diff the outputs of two commands?

Question

How can I use the diff command to compare 2 commands' outputs?

Does something like this exist?

diff  ($cat /etc/passwd) ($cut -f2/etc/passwd)

Of course, if one of the commands is really a `cat` with a single file argument, there's no obvious reason not to use that filename as one of the arguments to `diff`. — G-Man Says 'Reinstate Monica', Sep 16 '14 at 16:03
same question on stackoverflow with 250+ votes: https://stackoverflow.com/questions/3800202/diff-output-from-two-programs-without-temporary-files — Trevor Boyd Smith, Aug 01 '17 at 18:02

John1024 · Accepted Answer · 2016-10-14T01:46:45.953

77

Use process substitution:

diff <(cat /etc/passwd) <(cut -f2 /etc/passwd)

<(...) is called process substitution. It converts the output of a command into a file-like object that diff can read from.

While process substitution is not POSIX, it is supported by bash, ksh, and zsh.

edited Oct 14 '16 at 01:46

answered Sep 16 '14 at 05:39

John1024

score 9 · Answer 2 · edited Feb 13 '19 at 16:52

9

Difference between 2 commands output :-

$ diff <(command1) <(command2)

Difference between command output and file :-

$ diff <(command) filename

Difference between 2 files :-

$ diff file1 file2

e.g. $ diff <(mount) <(cat /proc/mounts)

edited Feb 13 '19 at 16:52

johan

answered Jun 24 '17 at 05:03

Ashish Sharma

2 Answers2