man-pages/man1p/id.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "ID" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" id 
.SH NAME
id \- return user identity
.SH SYNOPSIS
.LP
\fBid\fP \fB[\fP\fIuser\fP\fB]\fP\fB
.br
.sp
id -G\fP\fB[\fP\fB-n\fP\fB] [\fP\fIuser\fP\fB]\fP\fB
.br
.sp
id -g\fP\fB[\fP\fB-nr\fP\fB] [\fP\fIuser\fP\fB]\fP\fB
.br
.sp
id -u\fP\fB[\fP\fB-nr\fP\fB] [\fP\fIuser\fP\fB]\fP\fB
.br
\fP
.SH DESCRIPTION
.LP
If no \fIuser\fP operand is provided, the \fIid\fP utility shall write
the user and group IDs and the corresponding user and
group names of the invoking process to standard output. If the effective
and real IDs do not match, both shall be written. If
multiple groups are supported by the underlying system (see the description
of {NGROUPS_MAX} in the System Interfaces volume of
IEEE\ Std\ 1003.1-2001), the supplementary group affiliations of the
invoking process shall also be written.
.LP
If a \fIuser\fP operand is provided and the process has the appropriate
privileges, the user and group IDs of the selected user
shall be written. In this case, effective IDs shall be assumed to
be identical to real IDs. If the selected user has more than one
allowable group membership listed in the group database, these shall
be written in the same manner as the supplementary groups
described in the preceding paragraph.
.SH OPTIONS
.LP
The \fIid\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following options shall be supported:
.TP 7
\fB-G\fP
Output all different group IDs (effective, real, and supplementary)
only, using the format \fB"%u\\n"\fP . If there is more
than one distinct group affiliation, output each such affiliation,
using the format \fB"\ %u"\fP , before the
<newline> is output.
.TP 7
\fB-g\fP
Output only the effective group ID, using the format \fB"%u\\n"\fP
\&.
.TP 7
\fB-n\fP
Output the name in the format \fB"%s"\fP instead of the numeric ID
using the format \fB"%u"\fP .
.TP 7
\fB-r\fP
Output the real ID instead of the effective ID.
.TP 7
\fB-u\fP
Output only the effective user ID, using the format \fB"%u\\n"\fP
\&.
.sp
.SH OPERANDS
.LP
The following operand shall be supported:
.TP 7
\fIuser\fP
The login name for which information is to be written.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIid\fP:
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error and
informative messages written to standard output.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
The following formats shall be used when the \fILC_MESSAGES\fP locale
category specifies the POSIX locale. In other locales,
the strings \fIuid\fP, \fIgid\fP, \fIeuid\fP, \fIegid\fP, and \fIgroups\fP
may be replaced with more appropriate strings
corresponding to the locale.
.sp
.RS
.nf

\fB"uid=%u(%s) gid=%u(%s)\\n", <\fP\fIreal user ID\fP\fB>, <\fP\fIuser-name\fP\fB>,
    <\fP\fIreal group ID\fP\fB>, <\fP\fIgroup-name\fP\fB>
\fP
.fi
.RE
.LP
If the effective and real user IDs do not match, the following shall
be inserted immediately before the \fB'\\n'\fP character
in the previous format:
.sp
.RS
.nf

\fB" euid=%u(%s)"
\fP
.fi
.RE
.LP
with the following arguments added at the end of the argument list:
.sp
.RS
.nf

\fB<\fP\fIeffective user ID\fP\fB>, <\fP\fIeffective user-name\fP\fB>
\fP
.fi
.RE
.LP
If the effective and real group IDs do not match, the following shall
be inserted directly before the \fB'\\n'\fP character in
the format string (and after any addition resulting from the effective
and real user IDs not matching):
.sp
.RS
.nf

\fB" egid=%u(%s)"
\fP
.fi
.RE
.LP
with the following arguments added at the end of the argument list:
.sp
.RS
.nf

\fB<\fP\fIeffective group-ID\fP\fB>, <\fP\fIeffective group name\fP\fB>
\fP
.fi
.RE
.LP
If the process has supplementary group affiliations or the selected
user is allowed to belong to multiple groups, the first
shall be added directly before the <newline> in the format string:
.sp
.RS
.nf

\fB" groups=%u(%s)"
\fP
.fi
.RE
.LP
with the following arguments added at the end of the argument list:
.sp
.RS
.nf

\fB<\fP\fIsupplementary group ID\fP\fB>, <\fP\fIsupplementary group name\fP\fB>
\fP
.fi
.RE
.LP
and the necessary number of the following added after that for any
remaining supplementary group IDs:
.sp
.RS
.nf

\fB",%u(%s)"
\fP
.fi
.RE
.LP
and the necessary number of the following arguments added at the end
of the argument list:
.sp
.RS
.nf

\fB<\fP\fIsupplementary group ID\fP\fB>, <\fP\fIsupplementary group name\fP\fB>
\fP
.fi
.RE
.LP
If any of the user ID, group ID, effective user ID, effective group
ID, or supplementary/multiple group IDs cannot be mapped by
the system into printable user or group names, the corresponding \fB"(%s)"\fP
and \fIname\fP argument shall be omitted from the
corresponding format string.
.LP
When any of the options are specified, the output format shall be
as described in the OPTIONS section.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
Successful completion.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
Output produced by the \fB-G\fP option and by the default case could
potentially produce very long lines on systems that
support large numbers of supplementary groups. (On systems with user
and group IDs that are 32-bit integers and with group names
with a maximum of 8 bytes per name, 93 supplementary groups plus distinct
effective and real group and user IDs could theoretically
overflow the 2048-byte {LINE_MAX} text file line limit on the default
output case. It would take about 186 supplementary groups to
overflow the 2048-byte barrier using \fIid\fP \fB-G\fP). This is not
expected to be a problem in practice, but in cases where it
is a concern, applications should consider using \fIfold\fP \fB-s\fP
before postprocessing
the output of \fIid\fP.
.SH EXAMPLES
.LP
None.
.SH RATIONALE
.LP
The functionality provided by the 4 BSD \fIgroups\fP utility can be
simulated using:
.sp
.RS
.nf

\fBid -Gn [ user ]
\fP
.fi
.RE
.LP
The 4 BSD command \fIgroups\fP was considered, but it was not included
because it did not provide the functionality of the
\fIid\fP utility of the SVID. Also, it was thought that it would be
easier to modify \fIid\fP to provide the additional
functionality necessary to systems with multiple groups than to invent
another command.
.LP
The options \fB-u\fP, \fB-g\fP, \fB-n\fP, and \fB-r\fP were added
to ease the use of \fIid\fP with shell commands
substitution. Without these options it is necessary to use some preprocessor
such as \fIsed\fP
to select the desired piece of information. Since output such as that
produced by:
.sp
.RS
.nf

\fBid -u -n
\fP
.fi
.RE
.LP
is frequently wanted, it seemed desirable to add the options.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIfold\fP , \fIlogname\fP , \fIwho\fP , the System
Interfaces volume of IEEE\ Std\ 1003.1-2001, \fIgetgid\fP(), \fIgetgroups\fP(),
\fIgetuid\fP()
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .