From a124089295bc8f501c15e4891b9a9c2d4aa15412 Mon Sep 17 00:00:00 2001
From: Dylan Lom <dylanlom@gmail.com>
Date: Mon, 22 Feb 2021 22:24:31 +1100
Subject: [PATCH] Rename line to lines

* It can now extract multiple lines, I'm not super excited about the
  code, but it works at least
* Add ADVANCE_PTR macro to util
---
 doc/line.1              | 17 ------------
 doc/lines.1             | 26 ++++++++++++++++++
 src/{line.c => lines.c} | 61 +++++++++++++++++++++++++++++++----------
 src/util.h              |  5 ++--
 4 files changed, 76 insertions(+), 33 deletions(-)
 delete mode 100644 doc/line.1
 create mode 100644 doc/lines.1
 rename src/{line.c => lines.c} (51%)

diff --git a/doc/line.1 b/doc/line.1
deleted file mode 100644
index f608585..0000000
--- a/doc/line.1
+++ /dev/null
@@ -1,17 +0,0 @@
-.TH LINE 1
-.SH NAME
-line \- extract line from input
-.SH SYNOPSIS
-.B line
-.IR ln
-.SH DESCRIPTION
-.B line
-extracts the ln'th line from input provided over STDIN
-.SH EXAMPLES
-Get the 3rd line from the file line.1
-.PP
-.nf
-.RS
-line 3 < line.1
-.RE
-.fi
diff --git a/doc/lines.1 b/doc/lines.1
new file mode 100644
index 0000000..77a0f60
--- /dev/null
+++ b/doc/lines.1
@@ -0,0 +1,26 @@
+.TH LINES 1
+.SH NAME
+line \- extract lines from input
+.SH SYNOPSIS
+.B line
+.IR [LINES...]
+.SH DESCRIPTION
+.B line
+extracts lines from stdin. If multiple lines are provided, they will be sorted
+numerically. If the same line is specified twice, it will only be extracted
+once.
+.SH EXAMPLES
+Get the 3rd line from the file line.1
+.PP
+.nf
+.RS
+line 3 < line.1
+.RE
+.fi
+Get the 3rd, 4th and 5th lines from the file line.1
+.PP
+.nf
+.RS
+line 3 5 4 < line.1
+.RE
+.fi
diff --git a/src/line.c b/src/lines.c
similarity index 51%
rename from src/line.c
rename to src/lines.c
index 5dc5246..65b288f 100644
--- a/src/line.c
+++ b/src/lines.c
@@ -26,40 +26,73 @@ const char *argv0;
 void
 usage()
 {
-    die("usage: %s ln", argv0);
+    die("usage: %s [LINE...]", argv0);
+}
+
+int
+getlineno(const char *s)
+{
+    int ln;
+    char *p;
+    ln = (int)strtol(s, &p, 10);
+    if (errno != 0 || *p != '\0' || ln <= 0) {
+        errno ? edie("strtol: ") : die("unable to parse line");
+    }
+    return ln;
+}
+
+/* Insert ln into lns, assuming it is lns_size long and 0 initialised */
+int *
+insertln(int ln, int *lns, size_t lns_size)
+{
+    int *ip = lns;
+    int j;
+
+    while (lns_size && *ip && *ip < ln) {
+        ADVANCE_PTR(ip, lns_size);
+    }
+
+    while (lns_size) {
+        j = *ip;
+        *ip = ln;
+        ln = j;
+        ADVANCE_PTR(ip, lns_size);
+    }
+
+    return lns;
 }
 
-/* Print the ln'th line from fp to stdout */
 void
-line(FILE *fp, int ln)
+printlines(FILE *fp, int *lns, size_t lns_size)
 {
     char c;
     int cln = 1;
-    while ((c = fgetc(fp)) != '\0') {
-        if (cln > ln) break;
-        if (cln == ln) putc(c, stdout);
+    while (lns_size && (c = fgetc(fp)) != '\0') {
+        if (cln > *lns) { ADVANCE_PTR(lns, lns_size); }
+        if (cln == *lns) putc(c, stdout);
         if (c == '\n') cln++;
     }
 }
 
-/* Print a specified line from stdin */
+/* Print specified lines from stdin */
 int
 main(int argc, char *argv[])
 {
+    int *lns;
     SET_ARGV0();
 
     if (argc < 1) usage();
-    int ln;
-    char *p;
-    ln = (int)strtol(argv[0], &p, 10);
-    if (errno != 0 || *p != '\0') {
-        errno ? edie("strtol: ") : die("unable to parse ln");
+    size_t lns_size = argc;
+    lns = ecalloc(lns_size, sizeof(int));
+
+    while (argc) {
+        lns = insertln(getlineno(argv[0]), lns, lns_size);
+        SHIFT_ARGS();
     }
-    SHIFT_ARGS();
 
     FILE *fp;
     fp = fdopen(STDIN_FILENO, "r");
-    line(fp, ln);
+    printlines(fp, lns, lns_size);
     return 0;
 }
 
diff --git a/src/util.h b/src/util.h
index 1b185bc..ff61bc7 100644
--- a/src/util.h
+++ b/src/util.h
@@ -1,7 +1,8 @@
 /* SEE COPYRIGHT NOTICE IN util.c */
 
-#define SHIFT_ARGS() argv++; argc--;
-#define SET_ARGV0()  argv0 = argv[0]; SHIFT_ARGS();
+#define  ADVANCE_PTR(ptr, size) (ptr)++; (size)--
+#define  SHIFT_ARGS() ADVANCE_PTR(argv, argc)
+#define  SET_ARGV0()  argv0 = argv[0]; SHIFT_ARGS();
 
 void     die(const char *fmt, ...);
 void     edie(const char *fmt, ...);