xref: /freebsd/usr.bin/cmp/cmp.1 (revision bdcbfde31e8e9b343f113a1956384bdf30d1ed62)

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.Dd September 23, 2021
.Dt CMP 1
.Os
.Sh NAME
.Nm cmp
.Nd compare two files
.Sh SYNOPSIS
.Nm
.Op Fl l | s | x
.Op Fl bhz
.Op Fl -ignore-initial Ns Cm = Ns Ar num1 Ns Op :num2
.Op Fl -bytes Ns Cm = Ns Ar num
.Ar file1 file2
.Op Ar skip1 Op Ar skip2
.Sh DESCRIPTION
The
.Nm
utility compares two files of any type and writes the results
to the standard output.
By default,
.Nm
is silent if the files are the same; if they differ, the byte
and line number at which the first difference occurred is reported.
.Pp
Bytes and lines are numbered beginning with one.
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl b , Fl -print-bytes
Print each byte when a difference is found.
.It Fl h
Do not follow symbolic links.
.It Fl i Ar num1 Ns Oo :num2 Oc , Fl -ignore-initial= Ns Ar num1 Ns Op :num2
Skip
.Ar num1
bytes from
.Ar file1 ,
and optionally skip
.Ar num2
bytes from
.Ar file2 .
If
.Ar num2
is not specified, then
.Ar num1
is applied for both
.Ar file1
and
.Ar file2 .
.It Fl l , Fl -verbose
Print the byte number (decimal) and the differing
byte values (octal) for each difference.
.It Fl n Ar num , Fl -bytes= Ns num
Only compare up to
.Ar num
bytes.
.It Fl s , Fl -silent , Fl -quiet
Print nothing for differing files; return exit
status only.
.It Fl x
Like
.Fl l
but prints in hexadecimal and using zero as index
for the first byte in the files.
.It Fl z
For regular files compare file sizes first, and fail the comparison if they
are not equal.
.El
.Pp
The optional arguments
.Ar skip1
and
.Ar skip2
are the byte offsets from the beginning of
.Ar file1
and
.Ar file2 ,
respectively, where the comparison will begin.
The offset is decimal by default, but may be expressed as a hexadecimal
or octal value by preceding it with a leading ``0x'' or ``0''.
.Pp
.Ar skip1
and
.Ar skip2
may also be specified with SI size suffixes.
.Sh EXIT STATUS
The
.Nm
utility exits with one of the following values:
.Bl -tag -width 4n
.It 0
The files are identical.
.It 1
The files are different; this includes the case
where one file is identical to the first part of
the other.
In the latter case, if the
.Fl s
option has not been specified,
.Nm
writes to standard error that EOF was reached in the shorter
file (before any differences were found).
.It >1
An error occurred.
.El
.Sh EXAMPLES
Assuming a file named
.Pa example.txt
with the following contents:
.Bd -literal -offset indent
a
b
c
.Ed
.Pp
Compare stdin with
.Pa example.txt :
.Bd -literal -offset indent
$ echo -e "a\\nb\\nc" | cmp - example.txt
.Ed
.Pp
Same as above but introducing a change in the third byte of stdin.
Show the byte number (decimal) and differing byte (octal):
.Bd -literal -offset indent
$ echo -e "a\\nR\\nc" | cmp -l - example.txt
     3 122 142
.Ed
.Pp
Compare file sizes of
.Pa example.txt
and
.Pa /boot/loader.conf
and return 1 if they are not equal.
Note that
.Fl z
can only be used with regular files:
.Bd -literal -offset indent
$ cmp -z example.txt /boot/loader.conf
example.txt /boot/loader.conf differ: size
.Ed
.Pp
Compare stdin with
.Pa example.txt
omitting the first 4 bytes from stdin and the first 2 bytes from
.Pa example.txt :
.Bd -literal -offset indent
$ echo -e "a\\nR\\nb\\nc" | cmp - example.txt 4 2
.Ed
.Sh SEE ALSO
.Xr diff 1 ,
.Xr diff3 1
.Sh STANDARDS
The
.Nm
utility is expected to be
.St -p1003.2
compatible.
The
.Fl b ,
.Fl h ,
.Fl i ,
.Fl n ,
.Fl x ,
and
.Fl z
options are extensions to the standard.
.Ar skip1
and
.Ar skip2
arguments are extensions to the standard.
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .
.Sh BUGS
The phrase
.Dq SI size suffixes
above refers to the traditional power of two convention, as described in
.Xr expand_number 3 .