Import peek(1) from trinity/src
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8
Makefile
8
Makefile
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@ -102,11 +102,15 @@ mm: build/bin/mm
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build/bin/mm: src/mm.c build
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$(CC) $(CFLAGS) -o $@ src/mm.c
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.PHONY: npc
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npc: build/bin/npc
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build/bin/npc: src/npc.c build
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$(CC) $(CFLAGAS) -o $@ src/npc.c
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$(CC) $(CFLAGS) -o $@ src/npc.c
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.PHONY: peek
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peek: build/bin/peek
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build/bin/peek: src/peek.c build
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$(CC) $(CFLAGS) -o $@ src/peek.c
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.PHONY: rpn
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rpn: build/bin/rpn
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@ -0,0 +1,116 @@
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.\" Copyright (c) 2023-2024 DTB <trinity@trinity.moe>
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.\"
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.\" This work is licensed under CC BY-SA 4.0. To see a copy of this license,
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.\" visit <http://creativecommons.org/licenses/by-sa/4.0/>.
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.TH PEEK 1
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.SH NAME
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peek \(en read from standard input, furtively
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.SH SYNOPSIS
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peek
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.RB ( -1enot )
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.RB ( -p
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.RB [ program
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.RB [ arguments... ]])
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.SH DESCRIPTION
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Peek reads input from standard input with terminal echo disabled, which may be
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useful to prevent secrets being spied upon by adversaries watching a user's
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screen.
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.SH OPTIONS
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.B -1
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.RS
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Limits input to a single line (stopping when the newline character is read).
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.RE
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.B -e
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.RS
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Configures peek to output to standard error.
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.RE
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.B -n
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.RS
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Prints ("iNcludes") the terminating character in outputs. This is nonsensical
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if not combined with the
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.B -1
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option.
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.RE
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.B -o
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.RS
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Configures peek to output to standard output.
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.RE
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.B -p
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.RS
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Configures peek to pipe output to an executed child program, e.g. a password
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hashing utility. This is provided as a convenience and to avoid potential
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insecurities resulting from programmer error in scripts.
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.RE
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.B -t
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.RS
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Makes peek exit if not run within a terminal.
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.RE
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.SH DIAGNOSTICS
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Peek prints an error message and exits with the appropriate status from
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sysexits.h(3) if it encounters an unrecoverable error.
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Peek tries to handle the signal SIGINT (^C) to ensure the user's terminal is
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still usable after premature termination; if the signal can't be handled, it
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prints an error message and continues. If peek is interrupted, it exits
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unsuccessfully, without an error message.
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.SH BUGS
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Accepting secrets in shell scripts is not adviseable in any context.
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If used in a safety-critical application it must be ensured that the
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environment with which peek is used is not compromised.
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On systems that support it, the ioctl(2) command TIOCSTI can be used to insert
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characters into the standard input going to peek. This doesn't allow snooping
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but can be used for general mischief.
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Peek will happily run without outputs, slurping input and doing nothing with
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it.
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.SH EXAMPLES
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This is a command line for POSIX sh(1), using POSIX env(1) to discard the
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environment except for PATH, and htpassword(1) from Apache's utilities to hash
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the input with the bcrypt algorithm, printing the resulting hash:
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.RS
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.R $ env -i PATH="$PATH" peek -1tp htpasswd -nBi _ | cut -d : -f 2
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.RE
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This is a POSIX sh(1) command line that lets a user blindly write into a text
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file, only able to see written lines. Some writers have the habit of
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prematurely revising their work and use tools like this to prevent it:
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.RS
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.R $ echo Input ^D to quit. && peek -eot >writing.txt
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.RE
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.SH AUTHOR
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Written by DTB <trinity@trinity.moe>.
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.SH COPYRIGHT
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Copyright (c) 2023-2024 DTB. License AGPLv3+: GNU AGPL version 3 or later
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<https://gnu.org/licenses/gpl.html>.
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.SH SEE ALSO
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env(1), ioctl(2), ioctl_tty(2), read(1), sh(1)
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@ -0,0 +1,159 @@
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/*
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* Copyright (c) 2023–2024 DTB <trinity@trinity.moe>
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*
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* This program is free software: you can redistribute it and/or modify it under
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* the terms of the GNU Affero General Public License as published by the Free
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* Software Foundation, either version 3 of the License, or (at your option) any
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* later version.
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*
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* This program is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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* FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
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* details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see https://www.gnu.org/licenses/.
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*/
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#include <signal.h> /* sigaction(2), signal(2), struct sigaction, SIGINT */
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#include <stdio.h> /* fclose(3), fdopen(3), fprintf(3), getc(3), perror(3),
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* putc(3), stderr, stdin, stdout, EOF, NULL */
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#include <stdlib.h> /* exit(3), size_t, EXIT_FAILURE */
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#include <string.h> /* strerror(3) */
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#if !defined EX_OK || !defined EX_OSERR || !defined EX_USAGE
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# include <sysexits.h>
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#endif
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#include <termios.h> /* tcgetattr(3), tcsetattr(3), struct termios, ECHO */
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#include <unistd.h> /* dup(2), execvp(3), fork(2), getopt(3), isatty(3),
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* pipe(2), STDIN_FILENO */
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static int oserr(char *s){ perror(s); return EX_OSERR; }
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static char *program_name = "peek";
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static int usage(char *s){
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fprintf(stderr, "Usage: %s (-1enot) (-p [program [arguments...]])\n",
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s == NULL ? program_name : s);
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return EX_USAGE;
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}
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/* Restores terminal echo; otherwise when a user ^Cs the terminal would
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* continue to not display typed text. If sig isn't zero, this will terminate
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* the program. */
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void restore_echo(int sig){
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static struct termios t;
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tcgetattr(STDIN_FILENO, &t);
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t.c_lflag |= ECHO;
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tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);
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if(sig != 0)
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exit(EXIT_FAILURE);
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else
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return;
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}
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int main(int argc, char *argv[]){
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int eof;
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char include_eof;
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FILE *outputs[] = {
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NULL /* stdout */,
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NULL /* stderr */,
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NULL /* -p */
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};
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int p[2] = {0, 0};
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if(argc < 1)
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usage(argv[0]);
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eof = EOF;
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include_eof = 0;
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{ /* options parsing */
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int c;
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while((c = getopt(argc, argv, "1enopt")) != -1)
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switch(c){
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case '1': eof = '\n'; break;
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case 'n': include_eof = 1; break;
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case 'o': outputs[0] = stdout; break;
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case 'e': outputs[1] = stderr; break;
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case 'p':
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if(pipe(p) != 0 || (outputs[2] = fdopen(p[1], "ab")) == NULL)
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return oserr(argv[0]);
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break;
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case 't':
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if(isatty(STDIN_FILENO) != 1){
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fprintf(stderr, "%s: Must be run in a terminal"
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" (option -t specified)\n", argv[0]);
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return EX_USAGE;
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}
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default: return usage(argv[0]);
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}
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}
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/* If -p is used there must be additional arguments. getopt(3) wouldn't
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* work for this because optarg would have to be one string to give to
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* system(3) or an equivalent and it would be a mess of parsing and
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* security issues. Any intended usage works with this slightly funkier
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* argument parsing, unintended usages work as happy coincidence. */
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if((argc > optind) == (outputs[2] == 0))
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return usage(argv[0]);
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if(outputs[2] != 0)
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switch(fork()){
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case 0:
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if(close(p[1]) == 0 && dup2(p[0], STDIN_FILENO) == STDIN_FILENO)
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execvp(argv[optind], &argv[optind]);
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case -1:
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return oserr(argv[0]);
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default:
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if(close(p[0]) != 0)
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return oserr(argv[0]);
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}
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{ /* install signal handler */
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/* There isn't a difference in functionality between the signal(2) and
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* sigaction(2) methods. sigaction(2) is vastly preferred for
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* portability but some configurations can only use signal(2). */
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/* Errors aren't terminating because the worst that happens is some
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* terminal phooeyness if things go awry. */
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#if defined _POSIX_C_SOURCE
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struct sigaction act = { 0 };
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act.sa_handler = restore_echo;
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if(sigaction(SIGINT, &act, NULL) != 0)
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perror(argv[0]);
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#else
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if(signal(SIGINT, restore_echo) == SIG_ERR)
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perror(argv[0]);
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#endif
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}
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{ /* banish terminal echo */
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struct termios t;
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tcgetattr(STDIN_FILENO, &t);
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t.c_lflag ^= ECHO;
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tcsetattr(STDIN_FILENO, TCSAFLUSH, &t);
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}
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{ /* actual input loop */
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int c;
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size_t i;
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do{ if((c = getc(stdin)) != eof || include_eof)
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for(i = 0; i < (sizeof outputs)/(sizeof *outputs); ++i)
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if(outputs[i] != NULL && putc(c, outputs[i]) == EOF){
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perror(argv[0]);
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if(outputs[i] != stdout && outputs[i] != stderr)
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fclose(outputs[i]);
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outputs[i] = NULL;
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}
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}while(c != eof);
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}
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restore_echo(0);
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return EX_OK;
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}
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