diff --git a/bin/bash_session.sh b/bin/bash_session.sh
new file mode 100644
index 0000000..93d5ec9
--- /dev/null
+++ b/bin/bash_session.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+# Opens up a hathifiles bash session.
+docker-compose up -d pushgateway
+docker-compose run --rm "hf" bash
+# Now do e.g. `bundle exec rspec` or whatever.
+# Exit to be done with the session.
+docker-compose down; yes | docker system prune
diff --git a/bin/rights_change.sh b/bin/rights_change.sh
new file mode 100644
index 0000000..88489fa
--- /dev/null
+++ b/bin/rights_change.sh
@@ -0,0 +1,68 @@
+#!/bin/bash
+
+# Compare 2 hathifiles and report which items have changed rights
+# from ic/bib in file1 to pd/bib in file2.
+#
+# Invoke thusly:
+# $ bash rights_change.sh f1 f2
+# Results end up in ic_to_pd_YYYYMMDD.txt.
+# Each record in the output are presumed to have changed from ic
+# to pd between the generation of the 2 files.
+# Script starts at the bottom.
+
+run(){
+    f1=$1
+    f2=$2
+    echo "Started"
+    # First, simplify input hathifiles to the data we want.
+    # All the ic/bib records from f1 into one file...
+    cut_sort $f1 ic > cut_sort_ic.tsv
+    # And all the pd/bib records from f2 into another file.
+    cut_sort $f2 pd > cut_sort_pd.tsv
+    # Then compare the 2 simplified files.
+    isodate=`date +'%Y%m%d'`
+    outfile="`pwd`/ic_to_pd_${isodate}.tsv"
+    diff_records cut_sort_ic.tsv cut_sort_pd.tsv > $outfile
+    echo -e "Wrote $outfile"
+    # Remove intermediate files
+    rm cut_sort_ic.tsv cut_sort_pd.tsv
+    echo "Finished"
+}
+
+# Turn a hathifile into fewer cols and sorted matching lines.
+# Matching means: has rights:$rights and reason:bib
+cut_sort(){
+    file=$1
+    rights=$2
+    # Get these cols from the hathifiles:
+    # 1 (id), 3 (rights), 14 (reason), 16 (govdoc),
+    # grep to only get lines matching $rights,
+    # and sort the output.
+    zcat -f $file |
+	cut -f1,3,14,16 |
+	grep -P "\t${rights}\tbib\t[01]$" |
+	collated_sort
+}
+
+# Compare 2 outputs from cut_sort, but only look at col 1 (id) and
+# col 4 (govdoc), meaning we will only output records that have the
+# same id + govdoc values in both files, meaning each output record
+# changed from ic to pd but kept the same govdoc status.
+diff_records(){
+    ic_file=$1
+    pd_file=$2
+    collated_comm -12 <(cut -f1,4 $ic_file) <(cut -f1,4 $pd_file)
+}
+
+# Sort and comm must use the same collation,
+# or comm won't think the files are sorted...
+# and the defaults may be different, so specify.
+collated_comm(){
+    LC_COLLATE=C comm $@
+}
+collated_sort(){
+    LC_COLLATE=C sort $@
+}
+
+# Script starts here.
+run $1 $2
diff --git a/spec/data/rights_change_file_1.txt b/spec/data/rights_change_file_1.txt
new file mode 100644
index 0000000..e3bbc7c
--- /dev/null
+++ b/spec/data/rights_change_file_1.txt
@@ -0,0 +1,2 @@
+mdp.39015027625402	deny	ic	000018677		MIU	990000186770106381	1613293			66014593	Go up for glory, by Bill Russell, as told to William McSweeny.	Coward-McCann [1966]	bib		0	1966	   	eng	BK	MIU	umich	umich	google		Russell, Bill, 1934-2022.
+mdp.39015003746396	deny	ic	000018677		MIU	990000186770106381	1613293			66014593	Go up for glory, by Bill Russell, as told to William McSweeny.	Coward-McCann [1966]	bib		0	1966	   	eng	BK	MIU	umich	umich	google		Russell, Bill, 1934-2022.
diff --git a/spec/data/rights_change_file_2.txt b/spec/data/rights_change_file_2.txt
new file mode 100644
index 0000000..d089032
--- /dev/null
+++ b/spec/data/rights_change_file_2.txt
@@ -0,0 +1,2 @@
+mdp.39015027625402	deny	ic	000018677		MIU	990000186770106381	1613293			66014593	Go up for glory, by Bill Russell, as told to William McSweeny.	Coward-McCann [1966]	bib		0	1966	   	eng	BK	MIU	umich	umich	google		Russell, Bill, 1934-2022.
+mdp.39015003746396	allow	pd	000018677		MIU	990000186770106381	1613293			66014593	Go up for glory, by Bill Russell, as told to William McSweeny.	Coward-McCann [1966]	bib		0	1966	   	eng	BK	MIU	umich	umich	google		Russell, Bill, 1934-2022.
diff --git a/spec/jobs/rights_change.rb b/spec/jobs/rights_change.rb
new file mode 100644
index 0000000..f1a853b
--- /dev/null
+++ b/spec/jobs/rights_change.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+RSpec.describe "bin/rights_change.sh" do
+  it "writes the expected report file" do
+    # Setup.
+    Dir.chdir("/tmp")
+    isodate = Time.now.strftime("%Y%m%d")
+    # Command to run:
+    cmd = [
+      "bash",
+      "/usr/src/app/bin/rights_change.sh",
+      "/usr/src/app/spec/data/rights_change_file_1.txt",
+      "/usr/src/app/spec/data/rights_change_file_2.txt"
+    ].join(" ")
+    # Expect this outfile
+    outfile = "/tmp/ic_to_pd_#{isodate}.tsv"
+    FileUtils.rm_f(outfile)
+    expect(File.exist?(outfile)).to be false
+    # Now do it.
+    system(cmd)
+    # Expect a file with a single line...
+    expect(File.exist?(outfile)).to be true
+    lines = File.read(outfile).split("\n")
+    expect(lines.count).to eq 1
+    # and that single line looks like this:
+    expect(lines).to eq ["mdp.39015003746396\t0"]
+    # Cleanup
+    FileUtils.rm_f(outfile)
+  end
+end