diff --git a/install/05-antlr.sh b/install/05-antlr.sh
index 2d87fe3d2861b137a648b05ae0b8b6442c055e7d..7185126c71b28baf9d8f3bfd868cefbef642dc8a 100755
--- a/install/05-antlr.sh
+++ b/install/05-antlr.sh
@@ -8,4 +8,4 @@ pip2 install --user --upgrade . || exit 1
 
 # Add .local/bin to PATH
 PATH_CMD='export PATH=$PATH:$HOME/.local/bin'
-grep "${PATH_CMD}" ${TASTE_PATHS} || echo "${PATH_CMD}" >> ${TASTE_PATHS}
+grep "${PATH_CMD}" ${TASTE_PATHS} >/dev/null || echo "${PATH_CMD}" >> ${TASTE_PATHS}
diff --git a/install/10_dmt.sh b/install/10_dmt.sh
index 8f7a44b6a78f292337579b8b585f7b43671313ff..e028c21e12c81c1b758f62ae9e4d894e77ffc285 100755
--- a/install/10_dmt.sh
+++ b/install/10_dmt.sh
@@ -8,4 +8,4 @@ pip3 install --user --upgrade . || exit 1
 
 # Add .local/bin to PATH
 PATH_CMD='export PATH=$PATH:$HOME/.local/bin'
-grep "${PATH_CMD}" ${TASTE_PATHS} || echo "${PATH_CMD}" >> ${TASTE_PATHS}
+grep "${PATH_CMD}" ${TASTE_PATHS} >/dev/null || echo "${PATH_CMD}" >> ${TASTE_PATHS}
diff --git a/install/15_asn1scc.sh b/install/15_asn1scc.sh
index 8970e392832a39d2230e7de4cc8ab7eba15c4eb9..904a0c55f4d812c1e95b0fa1e92a7f5dfc2137c0 100755
--- a/install/15_asn1scc.sh
+++ b/install/15_asn1scc.sh
@@ -9,4 +9,4 @@ wget -q -O - https://github.com/ttsiodras/asn1scc/releases/download/3.3.9/asn1sc
 
 # Add ~/tool-inst/share/asn1scc/ to PATH
 PATH_CMD='export PATH=$PATH:$HOME/tool-inst/share/asn1scc/'
-grep "${PATH_CMD}" ${TASTE_PATHS} || echo "${PATH_CMD}" >> ${TASTE_PATHS}
+grep "${PATH_CMD}" ${TASTE_PATHS} >/dev/null || echo "${PATH_CMD}" >> ${TASTE_PATHS}
diff --git a/install/20_msc.sh b/install/20_msc.sh
index b459b8ab763719aae0eadb80872dc7d78198f377..333a3a69098756198dc77394c4506bf3703eea59 100755
--- a/install/20_msc.sh
+++ b/install/20_msc.sh
@@ -1,6 +1,11 @@
 #!/bin/bash
 DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+
+# Build MSC tools
 cd $DIR/../taste-MSC/ || exit 1
 make || exit 1
 cp ./MSC-Antlr3/bin/msc2py.exe $HOME/.local/bin || exit 1
 cp ./MSC-Antlr3/bin/taste-extract-asn-from-design.exe $HOME/.local/bin || exit 1
+
+PATH_CMD='export PATH=$PATH:$HOME/.local/bin'
+grep "${PATH_CMD}" ${TASTE_PATHS} >/dev/null || echo "${PATH_CMD}" >> ${TASTE_PATHS}