diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..11d805c
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[subcheckout "gnulib"]
+	url = git://git.savannah.gnu.org/gnulib.git
+	path = gnulib
diff --git a/ChangeLog b/ChangeLog
index 094b793..f3c5a1e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2019-04-01  Bruno Haible  <bruno@clisp.org>
+
+	build: Separate git operations from build operations.
+	* gitsub.sh: New file, from gnulib.
+	* .gitmodules: New file.
+	* autogen.sh: Remove all git operations. Look at GNULIB_SRCDIR
+	environment variable. Ignore the GNULIB_TOOL environment variable.
+	* HACKING: Explain when to use gitsub.sh.
+
 2019-03-07  Bruno Haible  <bruno@clisp.org>
 
 	Avoid signed integer overflow during shifts.
diff --git a/HACKING b/HACKING
index 44b1d37..82e5a2c 100644
--- a/HACKING
+++ b/HACKING
@@ -49,8 +49,14 @@
 https://savannah.gnu.org/git/?group=libiconv .
 
 After fetching the sources from the Git repository, peek at the comments in
-autogen.sh, then run "./autogen.sh"; then you can proceed with "./configure"
-as usual.
+autogen.sh, then run
+  ./gitsub.sh pull
+  ./autogen.sh
+Then you can proceed with "./configure" as usual.
+
+Each time you want to update the source, do not only "git pull".  Instead do
+  git pull && ./gitsub.sh pull
+  ./autogen.sh
 
 
 Adding new encodings
diff --git a/autogen.sh b/autogen.sh
index 49281e7..f53e1bb 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -5,10 +5,9 @@
 # with new versions of autoconf or automake.
 #
 # This script requires autoconf-2.63..2.69 and automake-1.11..1.16 in the PATH.
-# It also requires either
-#   - the GNULIB_TOOL environment variable pointing to the gnulib-tool script
-#     in a gnulib checkout, or
-#   - the git program in the PATH and an internet connection.
+# If not used from a released tarball, it also requires either
+#   - the GNULIB_SRCDIR environment variable pointing to a gnulib checkout, or
+#   - a preceding invocation of './gitsub.sh pull'.
 # It also requires
 #   - the gperf program.
 
@@ -28,12 +27,6 @@
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 # Usage: ./autogen.sh [--skip-gnulib]
-#
-# Usage from a git checkout:                 ./autogen.sh
-# This uses an up-to-date gnulib checkout.
-#
-# Usage from a released tarball:             ./autogen.sh --skip-gnulib
-# This does not use a gnulib checkout.
 
 skip_gnulib=false
 while :; do
@@ -44,28 +37,29 @@
 done
 
 if test $skip_gnulib = false; then
-  if test -z "$GNULIB_TOOL"; then
-    # Check out gnulib in a subdirectory 'gnulib'.
-    if test -d gnulib; then
-      (cd gnulib && git pull)
-    else
-      git clone git://git.savannah.gnu.org/gnulib.git
-    fi
-    # Now it should contain a gnulib-tool.
-    if test -f gnulib/gnulib-tool; then
-      GNULIB_TOOL=`pwd`/gnulib/gnulib-tool
-    else
-      echo "** warning: gnulib-tool not found" 1>&2
-    fi
+  if test -n "$GNULIB_SRCDIR"; then
+    test -d "$GNULIB_SRCDIR" || {
+      echo "*** GNULIB_SRCDIR is set but does not point to an existing directory." 1>&2
+      exit 1
+    }
+  else
+    GNULIB_SRCDIR=`pwd`/gnulib
+    test -d "$GNULIB_SRCDIR" || {
+      echo "*** Subdirectory 'gnulib' does not yet exist. Use './gitsub.sh pull' to create it, or set the environment variable GNULIB_SRCDIR." 1>&2
+      exit 1
+    }
   fi
-  # Skip the gnulib-tool step if gnulib-tool was not found.
-  if test -n "$GNULIB_TOOL"; then
-    $GNULIB_TOOL --copy-file build-aux/ar-lib || exit $?
-    chmod a+x build-aux/ar-lib || exit $?
-    make -f Makefile.devel \
-         gnulib-clean srclib/Makefile.gnulib gnulib-imported-files \
-         GNULIB_TOOL="$GNULIB_TOOL"
-  fi
+  # Now it should contain a gnulib-tool.
+  GNULIB_TOOL="$GNULIB_SRCDIR/gnulib-tool"
+  test -f "$GNULIB_TOOL" || {
+    echo "*** gnulib-tool not found." 1>&2
+    exit 1
+  }
+  $GNULIB_TOOL --copy-file build-aux/ar-lib || exit $?
+  chmod a+x build-aux/ar-lib || exit $?
+  make -f Makefile.devel \
+       gnulib-clean srclib/Makefile.gnulib gnulib-imported-files \
+       GNULIB_TOOL="$GNULIB_TOOL"
 fi
 
 make -f Makefile.devel totally-clean all || exit $?
diff --git a/gitsub.sh b/gitsub.sh
new file mode 100755
index 0000000..9665198
--- /dev/null
+++ b/gitsub.sh
@@ -0,0 +1,483 @@
+#! /bin/sh
+#
+# Copyright (C) 2019 Free Software Foundation, Inc.
+# Written by Bruno Haible <bruno@clisp.org>, 2019.
+#
+# 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 3 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.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# Program that manages the subdirectories of a git checkout of a package
+# that come from other packages (called "dependency packages").
+#
+# This program is similar in spirit to 'git submodule', with three
+# essential differences:
+#
+#   1) Its options are easy to remember, and do not require knowledge of
+#      'git submodule'.
+#
+#   2) The developer may choose to work on a different checkout for each
+#      dependency package.  This is important when the developer is
+#      preparing simultaneous changes to the package and the dependency
+#      package, or is using the dependency package in several packages.
+#
+#      The developer indicates this different checkout by setting the
+#      environment variable <SUBDIR>_SRCDIR (e.g. GNULIB_SRCDIR) to point to it.
+#
+#   3) The package maintainer may choose to use or not use git submodules.
+#
+#      The advantages of management through a git submodule are:
+#        - Changes to the dependency package cannot suddenly break your package.
+#          In other words, when there is an incompatible change that will cause
+#          a breakage, you can fix things at your pace; you are not forced to
+#          cope with such breakages in an emergency.
+#        - When you need to make a change as a response to a change in the
+#          dependency package, your co-developers cannot accidentally mix things
+#          up (for example, use a combination of your newest change with an
+#          older version of the dependency package).
+#
+#      The advantages of management without a git submodule (just as a plain
+#      subdirectory, let's call it a "subcheckout") are:
+#        - The simplicity: you are conceptually always using the newest revision
+#          of the dependency package.
+#        - You don't have to remember to periodially upgrade the dependency.
+#          Upgrading the dependency is an implicit operation.
+
+# This program is meant to be copied to the top-level directory of the package,
+# together with a configuration file.  The configuration is supposed to be
+# named '.gitmodules' and to define:
+# * The git submodules, as described in "man 5 gitmodules" or
+#   <https://git-scm.com/docs/gitmodules>.  For example:
+#
+#       [submodule "gnulib"]
+#               url = git://git.savannah.gnu.org/gnulib.git
+#               path = gnulib
+#
+#   You don't add this piece of configuration to .gitmodules manually.  Instead,
+#   you would invoke
+#     $ git submodule add --name "gnulib" -- git://git.savannah.gnu.org/gnulib.git gnulib
+#
+# * The subdirectories that are not git submodules, in a similar syntax.  For
+#   example:
+#
+#       [subcheckout "gnulib"]
+#               url = git://git.savannah.gnu.org/gnulib.git
+#               path = gnulib
+#
+# Here the URL is the one used for anonymous checkouts of the dependency
+# package. If the developer needs a checkout with write access, they can
+# either set the GNULIB_SRCDIR environment variable to point to that checkout
+# or modify the gnulib/.git/config file to enter a different URL.
+
+scriptname="$0"
+scriptversion='2019-04-01'
+nl='
+'
+IFS=" ""	$nl"
+
+# func_usage
+# outputs to stdout the --help usage message.
+func_usage ()
+{
+  echo "\
+Usage: gitsub.sh pull [SUBDIR]
+       gitsub.sh upgrade [SUBDIR]
+       gitsub.sh checkout SUBDIR REVISION
+
+Operations:
+
+gitsub.sh pull [SUBDIR]
+        You should perform this operation after 'git clone ...' and after
+        every 'git pull'.
+        It brings your checkout in sync with what the other developers of
+        your package have committed and pushed.
+        If an environment variable <SUBDIR>_SRCDIR is set, with a non-empty
+        value, nothing is done for this SUBDIR.
+        If no SUBDIR is specified, the operation applies to all dependencies.
+
+gitsub.sh upgrade [SUBDIR]
+        You should perform this operation periodically, to ensure currency
+        of the dependency package revisions that you use.
+        This operation pulls and checks out the changes that the developers
+        of the dependency package have committed and pushed.
+        If an environment variable <SUBDIR>_SRCDIR is set, with a non-empty
+        value, nothing is done for this SUBDIR.
+        If no SUBDIR is specified, the operation applies to all dependencies.
+
+gitsub.sh checkout SUBDIR REVISION
+        Checks out a specific revision for a dependency package.
+        If an environment variable <SUBDIR>_SRCDIR is set, with a non-empty
+        value, this operation fails.
+
+This script requires the git program in the PATH and an internet connection.
+"
+}
+
+# func_version
+# outputs to stdout the --version message.
+func_version ()
+{
+  year=`echo "$scriptversion" | sed -e 's/^\(....\)-.*/\1/'`
+  echo "\
+gitsub.sh (GNU gnulib) $scriptversion
+Copyright (C) 2019-$year Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law.
+"
+  printf "Written by %s.\n" "Bruno Haible"
+}
+
+# func_fatal_error message
+# outputs to stderr a fatal error message, and terminates the program.
+# Input:
+# - scriptname               name of this program
+func_fatal_error ()
+{
+  echo "$scriptname: *** $1" 1>&2
+  echo "$scriptname: *** Stop." 1>&2
+  exit 1
+}
+
+# func_warning message
+# Outputs to stderr a warning message,
+func_warning ()
+{
+  echo "gitsub.sh: warning: $1" 1>&2
+}
+
+# func_note message
+# Outputs to stdout a note message,
+func_note ()
+{
+  echo "gitsub.sh: note: $1"
+}
+
+# Unset CDPATH.  Otherwise, output from 'cd dir' can surprise callers.
+(unset CDPATH) >/dev/null 2>&1 && unset CDPATH
+
+# Command-line option processing.
+mode=
+while test $# -gt 0; do
+  case "$1" in
+    --help | --hel | --he | --h )
+      func_usage
+      exit $? ;;
+    --version | --versio | --versi | --vers | --ver | --ve | --v )
+      func_version
+      exit $? ;;
+    -- )
+      # Stop option processing
+      shift
+      break ;;
+    -* )
+      echo "gitsub.sh: unknown option $1" 1>&2
+      echo "Try 'gitsub.sh --help' for more information." 1>&2
+      exit 1 ;;
+    * )
+      break ;;
+  esac
+done
+if test $# = 0; then
+  echo "gitsub.sh: missing operation argument" 1>&2
+  echo "Try 'gitsub.sh --help' for more information." 1>&2
+  exit 1
+fi
+case "$1" in
+  pull | upgrade | checkout )
+    mode="$1"
+    shift ;;
+  *)
+    echo "gitsub.sh: unknown operation '$1'" 1>&2
+    echo "Try 'gitsub.sh --help' for more information." 1>&2
+    exit 1 ;;
+esac
+if test $# = 2 && test $mode != checkout || test $# -gt 2; then
+  echo "gitsub.sh: too many arguments in '$mode' mode" 1>&2
+  echo "Try 'gitsub.sh --help' for more information." 1>&2
+  exit 1
+fi
+if test $# = 0 && test $mode = checkout; then
+  echo "gitsub.sh: too few arguments in '$mode' mode" 1>&2
+  echo "Try 'gitsub.sh --help' for more information." 1>&2
+  exit 1
+fi
+
+# Read the configuration.
+# Output:
+# - subcheckout_names        space-separated list of subcheckout names
+# - submodule_names          space-separated list of submodule names
+if test -f .gitmodules; then
+  subcheckout_names=`git config --file .gitmodules --get-regexp --name-only 'subcheckout\..*\.url' | sed -e 's/^subcheckout\.//' -e 's/\.url$//' | tr -d '\r' | tr '\n' ' '`
+  submodule_names=`git config --file .gitmodules --get-regexp --name-only 'submodule\..*\.url' | sed -e 's/^submodule\.//' -e 's/\.url$//' | tr -d '\r' | tr '\n' ' '`
+else
+  subcheckout_names=
+  submodule_names=
+fi
+
+# func_validate SUBDIR
+# Verifies that the state on the file system is in sync with the declarations
+# in the configuration file.
+# Input:
+# - subcheckout_names        space-separated list of subcheckout names
+# - submodule_names          space-separated list of submodule names
+# Output:
+# - srcdirvar                Environment that the user can set
+# - srcdir                   Value of the environment variable
+# - path                     if $srcdir = "": relative path of the subdirectory
+# - needs_init               if $srcdir = "" and $path is not yet initialized:
+#                            true
+# - url                      if $srcdir = "" and $path is not yet initialized:
+#                            the repository URL
+func_validate ()
+{
+  srcdirvar=`echo "$1" | LC_ALL=C sed -e 's/[^a-zA-Z0-9]/_/g' | LC_ALL=C tr '[a-z]' '[A-Z]'`"_SRCDIR"
+  eval 'srcdir=$'"$srcdirvar"
+  path=
+  url=
+  if test -n "$srcdir"; then
+    func_note "Ignoring '$1' because $srcdirvar is set."
+  else
+    found=false
+    needs_init=
+    case " $subcheckout_names " in *" $1 "*)
+      found=true
+      # It ought to be a subcheckout.
+      path=`git config --file .gitmodules "subcheckout.$1.path"`
+      if test -z "$path"; then
+        path="$1"
+      fi
+      if test -d "$path"; then
+        if test -d "$path/.git"; then
+          # It's a plain checkout.
+          :
+        else
+          if test -f "$path/.git"; then
+            # It's a submodule.
+            func_fatal_error "Subdirectory '$path' is supposed to be a plain checkout, but it is a submodule."
+          else
+            func_warning "Ignoring '$path' because it exists but is not a git checkout."
+          fi
+        fi
+      else
+        # The subdir does not yet exist.
+        needs_init=true
+        url=`git config --file .gitmodules "subcheckout.$1.url"`
+        if test -z "$url"; then
+          func_fatal_error "Property subcheckout.$1.url is not defined in .gitmodules"
+        fi
+      fi
+      ;;
+    esac
+    case " $submodule_names " in *" $1 "*)
+      found=true
+      # It ought to be a submodule.
+      path=`git config --file .gitmodules "submodule.$1.path"`
+      if test -z "$path"; then
+        path="$1"
+      fi
+      if test -d "$path"; then
+        if test -d "$path/.git" || test -f "$path/.git"; then
+          # It's likely a submodule.
+          :
+        else
+          path_if_empty=`find "$path" -prune -empty 2>/dev/null`
+          if test -n "$path_if_empty"; then
+            # The subdir is empty.
+            needs_init=true
+          else
+            # The subdir is not empty.
+            # It is important to report an error, because we don't want to erase
+            # the user's files and 'git submodule update gnulib' sometimes reports
+            # "fatal: destination path '$path' already exists and is not an empty directory."
+            # but sometimes does not.
+            func_fatal_error "Subdir '$path' exists but is not a git checkout."
+          fi
+        fi
+      else
+        # The subdir does not yet exist.
+        needs_init=true
+      fi
+      # Another way to determine needs_init could be:
+      # if git submodule status "$path" | grep '^-' > /dev/null; then
+      #   needs_init=true
+      # fi
+      if test -n "$needs_init"; then
+        url=`git config --file .gitmodules "submodule.$1.url"`
+        if test -z "$url"; then
+          func_fatal_error "Property submodule.$1.url is not defined in .gitmodules"
+        fi
+      fi
+      ;;
+    esac
+    if ! $found; then
+      func_fatal_error "Subdir '$1' is not configured as a subcheckout or a submodule in .gitmodules"
+    fi
+  fi
+}
+
+# func_cleanup_current_git_clone
+# Cleans up the current 'git clone' operation.
+# Input:
+# - path
+func_cleanup_current_git_clone ()
+{
+  rm -rf "$path"
+  func_fatal_error "git clone failed"
+}
+
+# func_pull SUBDIR
+# Implements the 'pull' operation.
+func_pull ()
+{
+  func_validate "$1"
+  if test -z "$srcdir"; then
+    case " $subcheckout_names " in *" $1 "*)
+      # It's a subcheckout.
+      if test -d "$path"; then
+        if test -d "$path/.git"; then
+          (cd "$path" && git pull) || func_fatal_error "git operation failed"
+        fi
+      else
+        # The subdir does not yet exist. Create a plain checkout.
+        trap func_cleanup_current_git_clone 1 2 13 15
+        git clone "$url" "$path" || func_cleanup_current_git_clone
+        trap - 1 2 13 15
+      fi
+      ;;
+    esac
+    case " $submodule_names " in *" $1 "*)
+      # It's a submodule.
+      if test -n "$needs_init"; then
+        # Create a submodule checkout.
+        git submodule init -- "$path" && git submodule update -- "$path" || func_fatal_error "git operation failed"
+      else
+        # See https://stackoverflow.com/questions/1030169/easy-way-to-pull-latest-of-all-git-submodules
+        # https://stackoverflow.com/questions/4611512/is-there-a-way-to-make-git-pull-automatically-update-submodules
+        git submodule update "$path" || func_fatal_error "git operation failed"
+      fi
+      ;;
+    esac
+  fi
+}
+
+# func_upgrade SUBDIR
+# Implements the 'upgrade' operation.
+func_upgrade ()
+{
+  func_validate "$1"
+  if test -z "$srcdir"; then
+    if test -d "$path"; then
+      case " $subcheckout_names " in *" $1 "*)
+        # It's a subcheckout.
+        if test -d "$path/.git"; then
+          (cd "$path" && git pull) || func_fatal_error "git operation failed"
+        fi
+        ;;
+      esac
+      case " $submodule_names " in *" $1 "*)
+        # It's a submodule.
+        if test -z "$needs_init"; then
+          (cd "$path" && git fetch && git merge origin/master) || func_fatal_error "git operation failed"
+        fi
+        ;;
+      esac
+    else
+      # The subdir does not yet exist.
+      func_fatal_error "Subdirectory '$path' does not exist yet. Use 'gitsub.sh pull' to create it."
+    fi
+  fi
+}
+
+# func_checkout SUBDIR REVISION
+# Implements the 'checkout' operation.
+func_checkout ()
+{
+  func_validate "$1"
+  if test -z "$srcdir"; then
+    if test -d "$path"; then
+      case " $subcheckout_names " in *" $1 "*)
+        # It's a subcheckout.
+        if test -d "$path/.git"; then
+          (cd "$path" && git checkout "$2") || func_fatal_error "git operation failed"
+        fi
+        ;;
+      esac
+      case " $submodule_names " in *" $1 "*)
+        # It's a submodule.
+        if test -z "$needs_init"; then
+          (cd "$path" && git checkout "$2") || func_fatal_error "git operation failed"
+        fi
+        ;;
+      esac
+    else
+      # The subdir does not yet exist.
+      func_fatal_error "Subdirectory '$path' does not exist yet. Use 'gitsub.sh pull' to create it."
+    fi
+  fi
+}
+
+case "$mode" in
+  pull )
+    if test $# = 0; then
+      for sub in $subcheckout_names $submodule_names; do
+        func_pull "$sub"
+      done
+    else
+      valid=false
+      for sub in $subcheckout_names $submodule_names; do
+        if test "$sub" = "$1"; then
+          valid=true
+        fi
+      done
+      if $valid; then
+        func_pull "$1"
+      else
+        func_fatal_error "Subdir '$1' is not configured as a subcheckout or a submodule in .gitmodules"
+      fi
+    fi
+    ;;
+
+  upgrade )
+    if test $# = 0; then
+      for sub in $subcheckout_names $submodule_names; do
+        func_upgrade "$sub"
+      done
+    else
+      valid=false
+      for sub in $subcheckout_names $submodule_names; do
+        if test "$sub" = "$1"; then
+          valid=true
+        fi
+      done
+      if $valid; then
+        func_upgrade "$1"
+      else
+        func_fatal_error "Subdir '$1' is not configured as a subcheckout or a submodule in .gitmodules"
+      fi
+    fi
+    ;;
+
+  checkout )
+    valid=false
+    for sub in $subcheckout_names $submodule_names; do
+      if test "$sub" = "$1"; then
+        valid=true
+      fi
+    done
+    if $valid; then
+      func_checkout "$1" "$2"
+    else
+      func_fatal_error "Subdir '$1' is not configured as a subcheckout or a submodule in .gitmodules"
+    fi
+    ;;
+esac