MantisBT - CMake
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IDProjectCategoryView StatusDate SubmittedLast Update
0015963CMakeCMakepublic2016-02-09 16:522016-06-10 14:21
ReporterBruce Adams 
Assigned To 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionno change required 
PlatformLinuxOSRedHatOS Version5, 6 & 7
Product VersionCMake 3.4.3 
Target VersionFixed in Version 
Summary0015963: strange behaviour running readlink via execute_process
DescriptionI'm trying to use readlink -f to get the absolute path to a shared library following all symlinks.

>readlink -f /opt/gcc4.9.3/lib64/libstdc++.so.6
/opt/gcc4.9.3/lib64/libstdc++.so.6.0.20

but when I do this in cmake it doesn't expand the full path E.g.

set(CPP11_PATH ${CMAKE_CURRENT_BINARY_DIR}/)
execute_process(COMMAND ldd ${CPP11_PATH} COMMAND grep libstdc++ COMMAND awk "{ print $3; }" OUTPUT_VARIABLE LIBSTDCPP_PATH)
message("LIBSTDCPP_PATH=${LIBSTDCPP_PATH}")
execute_process(COMMAND readlink -f ${LIBSTDCPP_PATH} OUTPUT_VARIABLE LIBSTDCPP_ABSPATH)
message("LIBSTDCPP_ABSPATH=${LIBSTDCPP_ABSPATH}")

prints:

LIBSTDCPP_PATH=/opt/gcc4.9.3/lib64/libstdc++.so.6
LIBSTDCPP_ABSPATH=/opt/gcc4.9.3/lib64/libstdc++.so.6

This also happens if I wrap it in a shell script:

execute_process(COMMAND doreadlink.sh ${LIBSTDCPP_PATH} OUTPUT_VARIABLE LIBSTDCPP_ABSPATH2)
message("LIBSTDCPP_ABSPATH2=${LIBSTDCPP_ABSPATH2}")

>LIBSTDCPP_ABSPATH2=/opt/gcc4.9.3/lib64/libstdc++.so.6


Steps To Reproducecmake_minimum_required(VERSION 2.8)
project(TEST CXX)
CMake script as below

set(CPP11_PATH ${CMAKE_CURRENT_BINARY_DIR}/cpp11)
execute_process(COMMAND g++ ${CMAKE_CURRENT_SOURCE_DIR}/cpp11.cpp -o${CPP11_PATH})

execute_process(COMMAND ldd ${CPP11_PATH} COMMAND grep libstdc++ COMMAND awk "{ print $3; }" OUTPUT_VARIABLE LIBSTDCPP_PATH)
message("LIBSTDCPP_PATH=${LIBSTDCPP_PATH}")
execute_process(COMMAND readlink -f ${LIBSTDCPP_PATH} OUTPUT_VARIABLE LIBSTDCPP_ABSPATH)
message("LIBSTDCPP_ABSPATH=${LIBSTDCPP_ABSPATH}")
Additional InformationThe following is an effective work around

execute_process(COMMAND ldd ${CPP11_PATH} COMMAND grep libstdc++ COMMAND awk "{ print $3; }" COMMAND xargs readlink -f OUTPUT_VARIABLE LIBSTDCPP_PATH)

Originally raised on stackoverflow:

http://stackoverflow.com/questions/35299970/strange-behaviour-with-readlink-under-cmake [^]
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Issue History
Date ModifiedUsernameFieldChange
2016-02-09 16:52Bruce AdamsNew Issue
2016-02-09 16:56Bruce AdamsNote Added: 0040456
2016-02-09 17:52Bruce AdamsNote Added: 0040457
2016-02-10 08:55Brad KingStatusnew => resolved
2016-02-10 08:55Brad KingResolutionopen => no change required
2016-06-10 14:21Kitware RobotNote Added: 0041259
2016-06-10 14:21Kitware RobotStatusresolved => closed

Notes
(0040456)
Bruce Adams   
2016-02-09 16:56   
I can't think how this could be a bug. It must be some misunderstanding on my part as to how cmake works but it is not at all obvious what.
(0040457)
Bruce Adams   
2016-02-09 17:52   
This is user error not a bug. Please close. Sorry for wasting bandwidth!

awk "{ print $3; }"

adds a newline which causes readlink to return the original string rather than
expanding it.

awk "{ printf($3); }"

makes everything work as expected.
The same behaviour occurs using get_filename_component realpath.
(0041259)
Kitware Robot   
2016-06-10 14:21   
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