a framework for comparing present scripts execution with past ouput

mr_freeze.sh

#!/usr/bin/env bash
# Licence : fait tout ce que tu veux excepter dire que tu l'as écrit ou repomper sans citer jul
usage() {
cat << NAN
# $0 (freeze|thaw|prior_result) input

Blogpost-documentation generated by using \`$0 usage \` as a way to
try to have all in one place ;)

Source here : [https://gist.github.com/jul/ef4cbc4f506caace73c3c38b91cb1ea2](https://gist.github.com/jul/ef4cbc4f506caace73c3c38b91cb1ea2)

NAN

    cat <<'MAN'

A utility for comparing present scripts execution with past output

## Action
### freeze input

record the script given in input with ONE INSTRUCTION PER LINE to compare result for future use.

Except when **_OUTPUT** is set, output will automatically redirected to *replay_${input}*


### thaw input

replay the command in input (a frozen script output) and compare them with
past result


### prior_result input

show the past recorded value in the input file



## Quickstart

The code comes with its own testing data that are dumped in *input*

It is therefore possible to try the code with the following input :
```
$ PROD=1 ./mr_freeze.sh freeze input "badass" "b c"

```

to have the following output
```
✍️ recording: uname -a #immutable
✍️ recording: [ -n "$PROD" ] && echo "ok" || echo "ko" # mutable according to env variable
✍️ recording: date # mutable
✍️ recording: slmdkfmlsfs # immutable
✍️ recording: du -sh #immutable (kof kof)
✍️ recording: ssh "$A"  'uname -a'
✅ [input] recorded. Use [./mr_freeze.sh thaw "replay_input" "badass" "b c"] to replay
```

ofc, it works because I have a station called *badass* with an ssh server.

and then check what happens when you thaw the file accordingly.

```
$ ./mr_freeze.sh thaw "replay_input" "badass" "b c"

```

You have the following result:
```
👌 uname -a #immutable
🔥 [ -n "$PROD" ] && echo "ok" || echo "ko" # mutable according to env variable
@@ -1 +1 @@
-ok
+ko
🔥 date # mutable
@@ -1 +1 @@
-lun. 10 nov. 2025 20:21:14 CET
+lun. 10 nov. 2025 20:21:17 CET
👌 slmdkfmlsfs # immutable
👌 du -sh #immutable (kof kof)
👌 ssh "$A"  'uname -a'
```

Which means the commands replayed with same output except _date_ and the code checking for the env variable PROD and there is a diff of the output of the command.

Since the script is using subtituable variables (\$3 ... \$10) being remapped to (\$A ... \$H)

We can also change the target of the ssh command by doing :

```
$   PROD=1 ./mr_freeze.sh thaw "replay_input" "petiot"

```

which gives:
```
👌 uname -a #immutable
👌 [ -n "$PROD" ] && echo "ok" || echo "ko" # mutable according to env variable
🔥 date # mutable
@@ -1 +1 @@
-lun. 10 nov. 2025 20:21:14 CET
+lun. 10 nov. 2025 20:22:30 CET
👌 slmdkfmlsfs # immutable
👌 du -sh #immutable (kof kof)
🔥 ssh "$A"  'uname -a'
@@ -1 +1 @@
-Linux badass 6.8.0-85-generic #85-Ubuntu SMP PREEMPT_DYNAMIC Thu Sep 18 15:26:59 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
+FreeBSD petiot 14.3-RELEASE-p5 FreeBSD 14.3-RELEASE-p5 GENERIC amd64
```

It's also possible to change the output file by using _OUTPUT like this :
```
$ _OUTPUT=this ./mr_freeze.sh freeze input   badass
```
which will acknowledge the passed argument :
```
✅ [input] created use [./mr_freeze.sh thaw "this" "badass"] to replay
```

And last to check what has been recorded :
```
$ ./mr_freeze.sh prior_result this
```
which gives :

```
👉 uname -a #immutable
Linux badass 6.8.0-85-generic #85-Ubuntu SMP PREEMPT_DYNAMIC Thu Sep 18 15:26:59 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Status:0
--------------------------------------------------------------------------
👉 [ -n "$PROD" ] && echo "ok" || echo "ko" # mutable according to env variable
ok
Status:0
--------------------------------------------------------------------------
👉 date # mutable
lun. 10 nov. 2025 20:21:14 CET
Status:0
--------------------------------------------------------------------------
👉 slmdkfmlsfs # immutable
./mr_freeze.sh: ligne 165: slmdkfmlsfs : commande introuvable
Status:127
--------------------------------------------------------------------------
👉 du -sh #immutable (kof kof)
308K .
Status:0
--------------------------------------------------------------------------
👉 ssh "$A"  'uname -a'
Linux badass 6.8.0-85-generic #85-Ubuntu SMP PREEMPT_DYNAMIC Thu Sep 18 15:26:59 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Status:0
--------------------------------------------------------------------------
```



MAN
    if [ ! -z "$IS_SOURCE" ]; then
        return 1
    else
        exit 1
    fi
}
### next funny projet testing functional bash
map() {
    f=$1;
    shift
    while [ -n "$1" ]; do
        eval "$f" "$1"
        shift
    done

}
incr() { echo $(( $1 + 1 )); }

if_true() { if [[ "$1" != "0" && "$1" != "" ]]; then  echo "$1"; fi; }

filter() { map if_true $@ ;}

quote() { echo -n " \"$@\""; }

#echo $( map incr 1 2 3 4 5  )
#echo $( filter 1 0 1 0  )
### end of fun
cat <<'DATA' > input
uname -a #immutable
[ -n "$PROD" ] && echo "ok" || echo "ko" # mutable according to env variable
date # mutable
slmdkfmlsfs # immutable
du -sh #immutable (kof kof)
ssh "$A"  'uname -a'
DATA

ACTION=${1:-freeze}

INPUT=${2:-input}
shift 2

ARG=()
for v in A B C D E F G H; do
    eval export $v=\"$1\";
    ARG+=("$1")
    shift
done



_exec() {
    eval  "$@"  2>&1
    return $?
}

n2bl() { tr "\n" '\f' ;  }
bl2n() { tr "\f" '\n' ; }
HERE="# use $0 thaw replay_$INPUT to replay"

freeze() {
    INPUT=${1}
    OUTPUT=${_OUTPUT:-replay_${1}}

    while IFS=$'\a' read -r LINE; do
        echo "✍️ recording: $LINE"
        RES=$( _exec "$LINE" )
        ST="$?"
        RES=$( echo $RES | n2bl );

        HERE="$( echo -e "${HERE}\n$LINE\a$RES\a$ST\a$ST" )"
    done < "$INPUT"

    echo "$HERE" > $OUTPUT
    echo -n "✅ [${INPUT}] recorded. Use [$0 thaw \"$OUTPUT\" "
    echo -n $( map quote "${ARG[@]}")
    echo "] to replay"
}

prior_result() {
    INPUT=$1
    cat $INPUT | tail -n +2 | while IFS=$'\a' read -ra LINE; do
        echo -e "👉 ${LINE[0]}"
        echo -n ${LINE[1]}  | bl2n
        echo "Status:${LINE[2]}"
        echo "--------------------------------------------------------------------------"
    done
}

thaw() {
    INPUT=$1

    cat $INPUT | tail -n +2 | while IFS=$'\a' read -ra LINE; do
        FROM=$( echo ${LINE[1]}  | bl2n )
        ACTUAL=$( _exec ${LINE[0]}  )
        if [[ "$( echo $FROM | cat - )"  != "$( echo $ACTUAL | cat - )" ]]; then
        #if diff -q <( echo $FROM ) <( echo $ACTUAL ); then
            echo "🔥 ${LINE[0]} " 

            diff -ur --color=always <( echo "$FROM" )  <( echo "$ACTUAL" ) | tail -n +3
       else
            echo -e "👌 ${LINE[0]}"
       fi
    done
}

if [ "$0" = "$BASH_SOURCE" ]; then
    [ -z "$INPUT" ] && usage
    $ACTION $INPUT
else
    IS_SOURCE=1
    return 1
fi