add ci job to check local link issues

.github/scripts/local-link-checker.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+set -e
+set -u
+[ -n "${DEBUG:-}" ] && set -x || true
+
+function gherr() {
+  local line="$1"
+  local file="${line%%:*}"
+  local lineno="${line#*:}"
+  lineno="${lineno%%:*}"
+  local matching="${line#*:*:}"
+  echo "::error file=${file#./},line=$lineno::Broken link $matching"
+}
+
+function check() {
+  local line dir link target failed=0
+
+  while read line; do
+    dir="$(dirname "${line%%:*}")"
+    link="${line#*:*:}"
+
+    case "$link" in
+      //*)
+        # ignore http links
+        ;;
+      /*)
+        fail "Not a valid local link"
+        ;;
+      ../*)
+        target="$(dirname "$dir")${link#..}"
+        if ! [ -f "$target" ]; then
+          failed=1
+          gherr "$line"
+        fi
+        ;;
+      *)
+        # relative to current directory
+        target="$dir/${link#./}"
+        if ! [ -f "$target" ]; then
+          failed=1
+          gherr "$line"
+        fi
+        ;;
+    esac
+  done
+
+  exit "$failed"
+}
+
+find . -name '*.md' -print0 | xargs -0 /usr/bin/grep -Hno '[^(): ][^():]*\.md' | check

.github/workflows/local-link-checker.yaml

@@ -0,0 +1,21 @@
+name: Local Link Checker
+
+on:
+  push:
+    branches:
+      - "*"
+  pull_request:
+
+jobs:
+  local-link-checker:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: run checker
+      run: .github/scripts/local-link-checker.sh
+
+    - name: info for fixing
+      if: ${{ failure() }}
+      run: echo "Run ./.github/scripts/local-link-checker.sh to check locally"

.gitignore

@@ -3,4 +3,3 @@ _book
 .DS_Store
 *.pdf
 *.patch
-*.sh