diff options
| -rw-r--r-- | doc/s6-ln.html | 25 | ||||
| -rw-r--r-- | src/skaembutils/s6-ln.c | 8 |
2 files changed, 27 insertions, 6 deletions
diff --git a/doc/s6-ln.html b/doc/s6-ln.html index 3ca0245..1417c35 100644 --- a/doc/s6-ln.html +++ b/doc/s6-ln.html @@ -25,7 +25,7 @@ <h2> Interface </h2> <pre> - s6-ln [ -s ] [ -f ] [ -L ] [ -P ] <em>old</em> <em>new</em> + s6-ln [ -n ] [ -s ] [ -f ] [ -L ] [ -P ] <em>source...</em> <em>target</em> </pre> <p> @@ -33,12 +33,31 @@ <a href="http://pubs.opengroup.org/onlinepubs/9699919799/utilities/ln.html">ln</a> utility. </p> +<h2> Options </h2> + +<ul> + <li> <tt>-s</tt> : create a symbolic link instead of a hard link </li> + <li> <tt>-f</tt> : force replacement of an existing <em>target</em> </li> + <li> <tt>-L</tt> : link targets of symlinks in <em>source...</em> </li> + <li> <tt>-P</tt> : link symlinks in <em>source...</em> themselves </li> + <li> <tt>-n</tt> : if <em>target</em> is a symlink to a directory, replace +it instead of adding a link in the directory </li> +</ul> + <h2> Posixness </h2> <p> - s6-ln <strong>is</strong> suitable as a Single Unix + s6-ln <strong>would be</strong> suitable as a Single Unix <a href="http://pubs.opengroup.org/onlinepubs/9699919799/utilities/ln.html">ln</a> -program. +program, except that POSIX mandates that a preexisting <em>target</em> must first +be <tt>unlink()</tt>ed and then (<tt>sym</tt>)<tt>link()</tt>ed, which prevents +atomic replacements. + <tt>s6-ln</tt> aims to be reliable and allow for atomic replacements, so it +deviates from POSIX on that point: when <em>target</em> exists and needs to +be replaced, <tt>s6-ln</tt> first creates a (sym)link to a unique temporary +name, then <tt>rename()</tt>s the temporary name to <em>target</em>. This +behaviour makes sure that <em>target</em> is atomically replaced - there's +no point in time where it does not exist. </p> </body> diff --git a/src/skaembutils/s6-ln.c b/src/skaembutils/s6-ln.c index 59b85a4..65a650f 100644 --- a/src/skaembutils/s6-ln.c +++ b/src/skaembutils/s6-ln.c @@ -19,7 +19,7 @@ #include <skalibs/random.h> #include <skalibs/skamisc.h> -#define USAGE "s6-ln [ -s ] [ -f ] [ -L ] [ -P ] src... dest" +#define USAGE "s6-ln [ -n ] [ -s ] [ -f ] [ -L ] [ -P ] src... dest" typedef int linkfunc_t (char const *, char const *) ; typedef linkfunc_t *linkfunc_t_ref ; @@ -78,15 +78,17 @@ int main (int argc, char const *const *argv) { linkfunc_t_ref mylink = &link ; /* default to system behaviour */ ln_t_ref f = &noforce ; + int nodir = 0 ; PROG = "s6-ln" ; { subgetopt_t l = SUBGETOPT_ZERO ; for (;;) { - int opt = subgetopt_r(argc, argv, "sfLP", &l) ; + int opt = subgetopt_r(argc, argv, "nsfLP", &l) ; if (opt == -1) break ; switch (opt) { + case 'n' : nodir = 1 ; break ; case 's': mylink = &symlink ; break ; case 'f': f = &force ; break ; case 'L': if (mylink != &symlink) mylink = &linkderef ; break ; @@ -120,7 +122,7 @@ int main (int argc, char const *const *argv) { struct stat st ; - if (stat(argv[1], &st) < 0) + if (nodir ? lstat(argv[1], &st) : stat(argv[1], &st) < 0) { if (errno != ENOENT) strerr_diefu2sys(111, "stat ", argv[1]) ; (*f)(argv[0], argv[1], mylink) ; |