theory#79 apply requested changes on old bash compatibility

bin/pgenv

@@ -1360,14 +1360,15 @@ case $1 in
                 $PGENV_CURL -fLO ${PGENV_DOWNLOAD_ROOT}/v$v/${PG_TARBALL}
             fi
 
-            if [[ ${v%.*} -ge 17 ]]; then
+            # Starting from 17.x docs target might fail
+            # due to a missing dependency (docbooks-xsl).
+            # Download the docs tarball separately and
+            # install it after build.
+            if [[ $v =~ ^(1[789]|[2-9][0-9])\. ]]; then
                 PG_DOCS_TARBALL="postgresql-$v-docs.tar.gz"
-                DOCS_TAR_OPTS="zxf"
 
                 pgenv_debug "Downloading docs tarball"
 
-                # starting from 17.x docs target might fail
-                # due to a missing dependency (docbooks-xsl).
                 if [ ! -f $PG_DOCS_TARBALL ]; then
                     $PGENV_CURL -fLO ${PGENV_DOWNLOAD_ROOT}/v$v/${PG_DOCS_TARBALL}
                 fi
@@ -1425,10 +1426,10 @@ EOF
             # dependency for docs since 17.x and above, extracted
             # docs will be placed into the source directory,
             # as if they were built.
-            if [[ ${v%.*} -ge 17 ]]; then
+            if [[ $v =~ ^(1[789]|[2-9][0-9])\. ]]; then
                 pgenv_debug "Unpacking docs tarball"
 
-                $PGENV_TAR $DOCS_TAR_OPTS $PG_DOCS_TARBALL
+                $PGENV_TAR zxf $PG_DOCS_TARBALL
             fi
         fi