shelldiff.sh

#!/bin/sh

TMPDIR="$(mktemp -d)"

# Capture the default shell options, before we enter POSIX mode
set +o | sort > "$TMPDIR/shellopts.old"
echo "set -$-" >> "$TMPDIR/shellopts.old"
set -o posix

# Capture global variables
set | sort > "$TMPDIR/globals.old"

# Capture function names and definitions
declare -F | sort > "$TMPDIR/funcnames.old"
mkdir "$TMPDIR/funcs.old"
while read LINE; do
    FUNC_NAME=$(echo "$LINE" | cut -d ' ' -f 3)
    declare -f "$FUNC_NAME" > "$TMPDIR/funcs.old/$FUNC_NAME"
done < "$TMPDIR/funcnames.old"

# Reset shell options and source the file
(
    source "$TMPDIR/shellopts.old";
    source "$1";

    # Capture shell options
    set +o | sort > "$TMPDIR/shellopts.new"
    echo "set -$-" >> "$TMPDIR/shellopts.new"

    # Capture global variables
    set | sort > "$TMPDIR/globals.new"

    # Capture function names and definitions
    declare -F | sort > "$TMPDIR/funcnames.new"
    mkdir "$TMPDIR/funcs.new"
    while read LINE; do
        FUNC_NAME=$(echo "$LINE" | cut -d ' ' -f 3)
        declare -f "$FUNC_NAME" > "$TMPDIR/funcs.new/$FUNC_NAME"
    done < "$TMPDIR/funcnames.new"
)

# Output the shell options
cat "$TMPDIR/shellopts.new"

# Diff the global variables
diff \
    --new-line-format='+%L' \
    --old-line-format='-%L' \
    --unchanged-line-format=' %L' \
    "$TMPDIR/globals.old" \
    "$TMPDIR/globals.new" \
    > "$TMPDIR/globals.diff"
while read LINE; do
    FIRST=$(echo "$LINE" | cut -c 1)
    REST=$(echo "$LINE" | cut -c 2-)
    VARNAME=$(echo "$REST" | cut -d = -f 1)
    case "$FIRST" in
    +) echo "$REST" ;;
    -) echo "unset $VARNAME" ;;
    esac
done < "$TMPDIR/globals.diff"

# Diff the functions
diff \
    --new-line-format='+%L' \
    --old-line-format='-%L' \
    --unchanged-line-format=' %L' \
    "$TMPDIR/funcnames.old" \
    "$TMPDIR/funcnames.new" \
    > "$TMPDIR/funcnames.diff"
while read LINE; do
    FIRST=$(echo "$LINE" | cut -c 1)
    REST=$(echo "$LINE" | cut -c 2-)
    FUNC_NAME=$(echo "$REST" | cut -d ' ' -f 3)
    case "$FIRST" in
    +) cat "$TMPDIR/funcs.new/$FUNC_NAME" ;;
    -) echo "unset -f $FUNC_NAME" ;;
    *)
        if ! diff "$TMPDIR/funcs.old/$FUNC_NAME" "$TMPDIR/funcs.new/$FUNC_NAME" &>/dev/null; then
            cat "$TMPDIR/funcs.new/$FUNC_NAME"
        fi
        ;;
    esac
done < "$TMPDIR/funcnames.diff"

# Clean up temporary files
rm -Rf "$TMPDIR"

This garish script is hopefully a POSIX-compliant version of diffing the output of Bash's set before and after sourceing a shell script. The idea was to capture how loading virtual environment affects the shell session.

It captures shell options, global variables, and function definitions.

Future work:

• Handle aliases
• Handle read-only variables like Bash's SHELLOPTS
• Do not unset a modified variable, just change it
• Exclude shell options that did not change