[SOLVED] diff with file names prefixing each line

Issue

How can I diff two (or more) files, displaying the file name at the beginning of each line?

That is, instead of this:

--- file1.c
+++ file2.c
@@ -1 +1 @@
-int main() {
+int main(void) {

I would prefer something like this:

file1.c:- int main() {
file2.c:+ int main(void) {

This is not so useful when there are only two files, but extremely handy when using --from-file/--to-file.

Solution

I could not find a more concise solution, so I wrote my own script to do it, using several calls to diff to add a different prefix each time.

#!/bin/bash

# the first argument is the original file that others are compared with
orig=$1
len1=${#1}
shift

# we compute the length of the filenames to ensure they are aligned
for arg in "$@"
do
    len2=${#arg}
    maxlen=$((len1 > len2 ? len1 : len2))
    prefix1=$(printf "%-${maxlen}s" "$orig")
    prefix2=$(printf "%-${maxlen}s" "$arg")
    diff --old-line-format="$prefix1:-%L" \
         --new-line-format="$prefix2:+%L" \
         --unchanged-line-format="" $orig $arg
    echo "---" # not necessary, but helps visual separation
done

Answered By - anol

Answer Checked By - Clifford M. (WPSolving Volunteer)