rust-installer/install-template.sh: improve efficiency, step 1.

This round replaces repetitive pattern matching in the inner loop
of this script using grep (which causes a fork() for each test)
with built-in pattern matching in the bourne shell using the case
/ esac construct.

This in reference to
  #80684
and is a separated-out request from
  rust-lang/rust-installer#111

which apparently never got any review.

The forthcoming planned "step 2" change builds on top of this
change, and replaces the inner-loops needless uses of sed (which
again causes a fork() for each instance) with the suffix removal
constructs from the bourne shell.  Since this change touches lots
of the same lines this change does, that pull request cannot be
submitted before this one is accepted.

Hopefully this first step is less controversial than the
latter change.

Author: he32

src/tools/rust-installer/install-template.sh

@@ -551,54 +551,45 @@ install_components() {
         # Decide the destination of the file
         local _file_install_path="$_dest_prefix/$_file"
 
-        if echo "$_file" | grep "^etc/" > /dev/null
-        then
-        local _f="$(echo "$_file" | sed 's/^etc\///')"
-        _file_install_path="$CFG_SYSCONFDIR/$_f"
-        fi
-
-        if echo "$_file" | grep "^bin/" > /dev/null
-        then
-        local _f="$(echo "$_file" | sed 's/^bin\///')"
-        _file_install_path="$CFG_BINDIR/$_f"
-        fi
-
-        if echo "$_file" | grep "^lib/" > /dev/null
-        then
-        local _f="$(echo "$_file" | sed 's/^lib\///')"
-        _file_install_path="$CFG_LIBDIR/$_f"
-        fi
-
-        if echo "$_file" | grep "^share" > /dev/null
-        then
-        local _f="$(echo "$_file" | sed 's/^share\///')"
-        _file_install_path="$CFG_DATADIR/$_f"
-        fi
-
-        if echo "$_file" | grep "^share/man/" > /dev/null
-        then
-        local _f="$(echo "$_file" | sed 's/^share\/man\///')"
-        _file_install_path="$CFG_MANDIR/$_f"
-        fi
-
-            # HACK: Try to support overriding --docdir.  Paths with the form
-            # "share/doc/$product/" can be redirected to a single --docdir
-            # path. If the following detects that --docdir has been specified
-            # then it will replace everything preceding the "$product" path
-            # component. The problem here is that the combined rust installer
-            # contains two "products": rust and cargo; so the contents of those
-            # directories will both be dumped into the same directory; and the
-            # contents of those directories are _not_ disjoint. Since this feature
-            # is almost entirely to support 'make install' anyway I don't expect
-            # this problem to be a big deal in practice.
-            if [ "$CFG_DOCDIR" != "<default>" ]
-            then
-            if echo "$_file" | grep "^share/doc/" > /dev/null
-            then
-            local _f="$(echo "$_file" | sed 's/^share\/doc\/[^/]*\///')"
-            _file_install_path="$CFG_DOCDIR/$_f"
-            fi
-            fi
+        case "$_file" in
+            etc/*)
+                local _f="$(echo "$_file" | sed 's/^etc\///')"
+                _file_install_path="$CFG_SYSCONFDIR/$_f"
+                ;;
+            bin/*)
+                local _f="$(echo "$_file" | sed 's/^bin\///')"
+                _file_install_path="$CFG_BINDIR/$_f"
+                ;;
+            lib/*)
+                local _f="$(echo "$_file" | sed 's/^lib\///')"
+                _file_install_path="$CFG_LIBDIR/$_f"
+                ;;
+            share/man/*)
+                local _f="$(echo "$_file" | sed 's/^share\/man\///')"
+                _file_install_path="$CFG_MANDIR/$_f"
+                ;;
+            share/doc/*)
+                # HACK: Try to support overriding --docdir.  Paths with the form
+                # "share/doc/$product/" can be redirected to a single --docdir
+                # path. If the following detects that --docdir has been specified
+                # then it will replace everything preceding the "$product" path
+                # component. The problem here is that the combined rust installer
+                # contains two "products": rust and cargo; so the contents of those
+                # directories will both be dumped into the same directory; and the
+                # contents of those directories are _not_ disjoint. Since this feature
+                # is almost entirely to support 'make install' anyway I don't expect
+                # this problem to be a big deal in practice.
+                if [ "$CFG_DOCDIR" != "<default>" ]
+                then
+                    local _f="$(echo "$_file" | sed 's/^share\/doc\/[^/]*\///')"
+                    _file_install_path="$CFG_DOCDIR/$_f"
+                fi
+                ;;
+            share/*)
+                local _f="$(echo "$_file" | sed 's/^share\///')"
+                _file_install_path="$CFG_DATADIR/$_f"
+                ;;
+        esac
 
         # Make sure there's a directory for it
         make_dir_recursive "$(dirname "$_file_install_path")"
@@ -617,13 +608,20 @@ install_components() {
 
             maybe_backup_path "$_file_install_path"
 
-            if echo "$_file" | grep "^bin/" > /dev/null || test -x "$_src_dir/$_component/$_file"
-            then
-            run cp "$_src_dir/$_component/$_file" "$_file_install_path"
-            run chmod 755 "$_file_install_path"
+            if test -x "$_src_dir/$_component/$_file"; then
+                run cp "$_src_dir/$_component/$_file" "$_file_install_path"
+                run chmod 755 "$_file_install_path"
             else
-            run cp "$_src_dir/$_component/$_file" "$_file_install_path"
-            run chmod 644 "$_file_install_path"
+                case "$_file" in
+                    bin/*)
+                        run cp "$_src_dir/$_component/$_file" "$_file_install_path"
+                        run chmod 755 "$_file_install_path"
+                        ;;
+                    *)
+                        run cp "$_src_dir/$_component/$_file" "$_file_install_path"
+                        run chmod 644 "$_file_install_path"
+                        ;;
+                esac
             fi
             critical_need_ok "file creation failed"