Hi Paul,
Paul Eggert <egg...@cs.ucla.edu> writes:
> Thanks for looking into that. Unfortunately POSIX says -p should be
> ignored only if standard output is a terminal, and that newline should
> be read from /dev/tty, not from standard input. This is so that users
> can pipe into 'pr -p'. So the proposed patch needs some changes. Here
> are the issues I found:
Thanks for the thorough review.
I think that v3 attached should cover everything.
Collin
>From 79dc6d5cfbc45966cd039a599c7db372452b1a9a Mon Sep 17 00:00:00 2001
Message-ID: <79dc6d5cfbc45966cd039a599c7db372452b1a9a.1753669052.git.collin.fu...@gmail.com>
From: Collin Funk <collin.fu...@gmail.com>
Date: Sun, 27 Jul 2025 15:00:15 -0700
Subject: [PATCH v3] pr: implement '-p' as required by POSIX Issue 6
* src/pr.c (pause_option): New variable.
(tty_fp): Likewise.
(short_options): Add '-p'.
(long_options): Add '--pause'.
(main): Add the option. Ignore it if standard output is not a tty. Open
a 'FILE *' for /dev/tty and fail if any operations on it are
unsuccessful.
(print_files): If the option is use emit '\a' to stderr and wait until a
newline is read to print the next page.
(usage): Mention the new option.
* doc/coreutils.texi (pr invocation): Document the new option.
* NEWS: Mention the new option.
---
NEWS | 4 ++++
doc/coreutils.texi | 8 +++++++
src/pr.c | 55 +++++++++++++++++++++++++++++++++++++++++++---
3 files changed, 64 insertions(+), 3 deletions(-)
diff --git a/NEWS b/NEWS
index 0b2be7116..776932c69 100644
--- a/NEWS
+++ b/NEWS
@@ -64,6 +64,10 @@ GNU coreutils NEWS -*- outline -*-
Iranian locale (fa_IR) and for the Ethiopian locale (am_ET), and also
does so more consistently for the Thailand locale (th_TH.UTF-8).
+ pr now supports the -p option, to pause upon printing each page until
+ a newline character is read from /dev/tty, as required by POSIX Issue
+ 6. The corresponding long option is --pause.
+
* Noteworthy changes in release 9.7 (2025-04-09) [stable]
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 7ca5b222c..a8193f5ff 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -2825,6 +2825,14 @@ @node pr invocation
set with the @option{-W/-w} option. A limited overflow may occur with
numbered single column output (compare @option{-n} option).
+@item -p
+@itemx --pause
+@opindex -p
+@opindex --pause
+After printing each page, print an alert (bell) to standard error and
+wait for a newline to be read from @file{/dev/tty} before printing the
+next page. This option is ignored unless standard output is a tty.
+
@item -r
@itemx --no-file-warnings
@opindex -r
diff --git a/src/pr.c b/src/pr.c
index e7081a059..22e752675 100644
--- a/src/pr.c
+++ b/src/pr.c
@@ -711,6 +711,12 @@ static char *custom_header;
/* (-D) Date format for the header. */
static char const *date_format;
+/* If true, pause after each page until a newline is read from /dev/tty. */
+static bool pause_option;
+
+/* Used to read from /dev/tty if --p/--pause is in use. */
+static FILE *tty_fp;
+
/* The local time zone rules, as per the TZ environment variable. */
static timezone_t localtz;
@@ -738,7 +744,7 @@ enum
};
static char const short_options[] =
- "-0123456789D:FJN:S::TW:abcde::fh:i::l:mn::o:rs::tvw:";
+ "-0123456789D:FJN:S::TW:abcde::fh:i::l:mn::po:rs::tvw:";
static struct option const long_options[] =
{
@@ -758,6 +764,7 @@ static struct option const long_options[] =
{"number-lines", optional_argument, nullptr, 'n'},
{"first-line-number", required_argument, nullptr, 'N'},
{"indent", required_argument, nullptr, 'o'},
+ {"pause", no_argument, nullptr, 'p'},
{"no-file-warnings", no_argument, nullptr, 'r'},
{"separator", optional_argument, nullptr, 's'},
{"sep-string", optional_argument, nullptr, 'S'},
@@ -999,6 +1006,9 @@ main (int argc, char **argv)
chars_per_margin = getoptnum (optarg, 0,
_("'-o MARGIN' invalid line offset"));
break;
+ case 'p':
+ pause_option = true;
+ break;
case 'r':
ignore_failed_opens = true;
break;
@@ -1079,6 +1089,18 @@ main (int argc, char **argv)
error (EXIT_FAILURE, 0,
_("cannot specify both printing across and printing in parallel"));
+ if (pause_option)
+ {
+ pause_option = isatty (STDOUT_FILENO);
+ if (pause_option)
+ {
+ tty_fp = fopen ("/dev/tty", "r");
+ if (tty_fp == nullptr)
+ error (EXIT_FAILURE, errno, _("cannot open %s for reading"),
+ quoteaf ("/dev/tty"));
+ }
+ }
+
/* Translate some old short options to new/long options.
To meet downward compatibility with other UNIX pr utilities
and some POSIX specifications. */
@@ -1149,6 +1171,8 @@ main (int argc, char **argv)
if (have_read_stdin && fclose (stdin) == EOF)
error (EXIT_FAILURE, errno, _("standard input"));
+ if (pause_option && fclose (tty_fp) == EOF)
+ error (EXIT_FAILURE, errno, "%s", quotef ("/dev/tty"));
main_exit (failed_opens ? EXIT_FAILURE : EXIT_SUCCESS);
}
@@ -1636,8 +1660,31 @@ print_files (int number_of_files, char **av)
init_funcs ();
line_number = line_count;
- while (print_page ())
- ;
+ for (;;)
+ {
+ if (pause_option)
+ {
+ if (putc ('\a', stderr) == EOF || fflush (stderr) != 0)
+ write_error ();
+ for (;;)
+ {
+ int ch = getc (tty_fp);
+ if (ch == EOF)
+ {
+ /* Just exit if the user presses Ctrl-D. */
+ if (feof (tty_fp))
+ goto finish;
+ error (EXIT_FAILURE, errno, _("error reading %s"),
+ quoteaf ("/dev/tty"));
+ }
+ if (ch == '\n')
+ break;
+ }
+ }
+ if (! print_page ())
+ break;
+ }
+ finish:
}
/* Initialize header information.
@@ -2824,6 +2871,8 @@ Paginate or columnate FILE(s) for printing.\n\
-o, --indent=MARGIN\n\
offset each line with MARGIN (zero) spaces, do not\n\
affect -w or -W, MARGIN will be added to PAGE_WIDTH\n\
+ -p, --pause pause at the beginning of each page until a newline\n\
+ is read from /dev/tty.\n\
-r, --no-file-warnings\n\
omit warning when a file cannot be opened\n\
"), stdout);
--
2.50.1
