[hackers] [sbase] We should not require both files to be present for cmp(1) || sin

[git]

commit c28e2a39ecf560291a68db3d506a5d2177c7a80d
Author: sin <s...@2f30.org>
Date:   Tue Mar 4 10:33:51 2014 +0000

    We should not require both files to be present for cmp(1)
    
    If the second file is not present, read from standard input.

diff --git a/cmp.c b/cmp.c
index 6bc97cc..9c0b316 100644
--- a/cmp.c
+++ b/cmp.c
@@ -10,7 +10,7 @@ enum { Same = 0, Diff = 1, Error = 2 };
 static void
 usage(void)
 {
-       enprintf(Error, "usage: %s [-ls] file1 file2
", argv0);
+       enprintf(Error, "usage: %s [-ls] file1 [file2]
", argv0);
 }
 
 int
@@ -34,13 +34,19 @@ main(int argc, char *argv[])
                usage();
        } ARGEND;
 
-       if(argc < 2)
+       if (argc < 1 || argc > 2)
                usage();
 
-       for(i = 0; i < 2; i++) {
-               if(!(fp[i] = fopen(argv[i], "r")))
-                       enprintf(Error, "fopen %s:", argv[i]);
-       }
+       fp[0] = fopen(argv[0], "r");
+       if (!fp[0])
+               enprintf(Error, "fopen %s:", argv[0]);
+       fp[1] = stdin;
+
+       if (argc == 2)
+               fp[1] = fopen(argv[1], "r");
+               if (!fp[1])
+                       enprintf(Error, "fopen %s:", argv[1]);
+
        for(n = 1; ((b[0] = getc(fp[0])) != EOF) \
                        | ((b[1] = getc(fp[1])) != EOF); n++) {
                if(b[0] == '
')
@@ -49,11 +55,12 @@ main(int argc, char *argv[])
                        continue;
                for(i = 0; i < 2; i++)
                        if(b[i] == EOF)
-                               enprintf(Diff, "cmp: EOF on %s
", argv[i]);
+                               enprintf(Diff, "cmp: EOF on %s
",
+                                        !argv[i] ? "<stdin>" : argv[1]);
                if(!lflag) {
                        if(!sflag)
                                printf("%s %s differ: char %ld, line %ld
",
-                                      argv[0], argv[1], n, line);
+                                      argv[0], !argv[1] ? "<stdin>" : argv[1], 
n, line);
                        exit(Diff);
                } else {
                        printf("%4ld %3o %3o
", n, b[0], b[1]);
@@ -62,4 +69,3 @@ main(int argc, char *argv[])
        }
        return same ? Same : Diff;
 }
-