filter-branch: stop depending on Perl

While git-filter-branch(1) is written as a shell script, the
`--state-branch` feature depends on Perl to save and extract the object
ID mappings. This can lead to subtle breakage though:

  - We execute `perl` directly without respecting the `PERL_PATH`
    configured by the distribution. As such, it may happen that we use
    the wrong version of Perl.

  - We install the script unchanged even if Perl isn't available at all
    on the system, so using `--state-branch` would lead to failure
    altogether in that case.

Fix this by dropping Perl and instead implementing the feature with
shell scripting exclusively.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 3a51d4507c7136722812f5dc10ee97a9af5b84a0..24fa317aaaa4ca8e9d79242b9eef7c7485333c40 100755 (executable)
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -295,15 +295,18 @@ then
        if test -n "$state_commit"
        then
                echo "Populating map from $state_branch ($state_commit)" 1>&2
-               perl -e'open(MAP, "-|", "git show $ARGV[0]:filter.map") or die;
-                       while (<MAP>) {
-                               m/(.*):(.*)/ or die;
-                               open F, ">../map/$1" or die;
-                               print F "$2" or die;
-                               close(F) or die;
-                       }
-                       close(MAP) or die;' "$state_commit" \
-                               || die "Unable to load state from $state_branch:filter.map"
+
+               git show "$state_commit:filter.map" >"$tempdir"/filter-map ||
+                       die "Unable to load state from $state_branch:filter.map"
+               while read line
+               do
+                       case "$line" in
+                       *:*)
+                               echo "${line%:*}" >../map/"${line#*:}";;
+                       *)
+                               die "Unable to load state from $state_branch:filter.map";;
+                       esac
+               done <"$tempdir"/filter-map
        else
                echo "Branch $state_branch does not exist. Will create" 1>&2
        fi
@@ -633,15 +636,13 @@ if test -n "$state_branch"
 then
        echo "Saving rewrite state to $state_branch" 1>&2
        state_blob=$(
-               perl -e'opendir D, "../map" or die;
-                       open H, "|-", "git hash-object -w --stdin" or die;
-                       foreach (sort readdir(D)) {
-                               next if m/^\.\.?$/;
-                               open F, "<../map/$_" or die;
-                               chomp($f = <F>);
-                               print H "$_:$f\n" or die;
-                       }
-                       close(H) or die;' || die "Unable to save state")
+               for file in ../map/*
+               do
+                       from_commit=$(basename "$file")
+                       to_commit=$(cat "$file")
+                       echo "$from_commit:$to_commit"
+               done | git hash-object -w --stdin || die "Unable to save state"
+       )
        state_tree=$(printf '100644 blob %s\tfilter.map\n' "$state_blob" | git mktree)
        if test -n "$state_commit"
        then