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'\"macro stdmacro
.\"
.\" Copyright (c) 2015,2019 Red Hat.
.\"
.\" This program is free software; you can redistribute it and/or modify it
.\" under the terms of the GNU General Public License as published by the
.\" Free Software Foundation; either version 2 of the License, or (at your
.\" option) any later version.
.\"
.\" This program is distributed in the hope that it will be useful, but
.\" WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
.\" or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
.\" for more details.
.\"
.\"
.TH PCP-PYTHON 1 "PCP" "Performance Co-Pilot"
.SH NAME
\f3pcp-python\f1 \- run a python script using a preferred python variant
.SH SYNOPSIS
\f3pcp\f1
\f3python\f1 [\f2SCRIPT\f1 [\f2ARG\f1] ...]
.SH DESCRIPTION
.B pcp-python
has been replaced by
.BR pmpython (1)
which is preferred, however
.B pcp-python
is still installed to provided backwards compatibility.
.PP
.B pcp-python
provides a way to run python scripts using a customisable python
binary, rather than embedding any particular version of python into
each script.
.PP
This can be useful as it allows version-independent python code to be
run anywhere.
All python modules shipped with PCP support versions
2.6 and later (in the python2 series), and 3.3 and later (in the python3
release series).
.PP
Due to python monitoring and collecting scripts being relatively simple
in PCP (not requiring new modules, language features, etc), it has been
possible to ensure they work for all of the above python versions.
Thus,
it is common for PCP python scripts to use a "shebang" line that invokes
.B pcp-python
as follows:
.PP
.in 1.0i
.ft CR
.nf
.I "#!/usr/bin/pcp python"
.fi
.ft R
.in
.PP
This allows the custom setting to be injected instead of a hard-coded
python version, while still allowing the user to override the python
version as follows:
.PP
.in 1.0i
.ft CR
.nf
.B "$ PCP_PYTHON_PROG=python3 /usr/bin/pcp python --version"
Python 3.3.2
.B "$ PCP_PYTHON_PROG=python2 /usr/bin/pcp python --version"
Python 2.7.5
.fi
.ft R
.in
.PP
This is convenient for shipping identical scripts on multiple platforms,
and for testing different python versions with the one script (e.g. in
the case where multiple versions of python are installed, PCP_PYTHON_PROG
can be set in the local environment to override the global setting).
.PP
By default, the value of PCP_PYTHON_PROG from
.I /etc/pcp.conf
will be used.
The default value of this configuration parameter is set depending on
some heuristics about the target build platform.
These heuristics favour the use of
.I python3
in all recent releases of PCP, for those platforms that support it.
.SH PCP ENVIRONMENT
Environment variables with the prefix \fBPCP_\fP are used to parameterize
the file and directory names used by PCP.
On each installation, the
file \fI/etc/pcp.conf\fP contains the local values for these variables.
The \fB$PCP_CONF\fP variable may be used to specify an alternative
configuration file, as described in \fBpcp.conf\fP(5).
.SH SEE ALSO
.BR PCPIntro (1)
and
.BR pcp (1).
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