1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Mini tail implementation for busybox
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4 | *
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5 | * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
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6 | *
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7 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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8 | */
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9 |
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10 | /* BB_AUDIT SUSv3 compliant (need fancy for -c) */
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11 | /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
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12 | /* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
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13 |
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14 | /* Mar 16, 2003 Manuel Novoa III (mjn3@codepoet.org)
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15 | *
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16 | * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
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17 | * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
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18 | * 1) mixing printf/write without fflush()ing stdout
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19 | * 2) no check that any open files are present
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20 | * 3) optstring had -q taking an arg
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21 | * 4) no error checking on write in some cases, and a warning even then
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22 | * 5) q and s interaction bug
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23 | * 6) no check for lseek error
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24 | * 7) lseek attempted when count==0 even if arg was +0 (from top)
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25 | */
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26 |
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27 | //usage:#define tail_trivial_usage
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28 | //usage: "[OPTIONS] [FILE]..."
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29 | //usage:#define tail_full_usage "\n\n"
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30 | //usage: "Print last 10 lines of each FILE (or stdin) to stdout.\n"
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31 | //usage: "With more than one FILE, precede each with a filename header.\n"
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32 | //usage: "\n -f Print data as file grows"
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33 | //usage: IF_FEATURE_FANCY_TAIL(
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34 | //usage: "\n -s SECONDS Wait SECONDS between reads with -f"
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35 | //usage: )
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36 | //usage: "\n -n N[kbm] Print last N lines"
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37 | //usage: IF_FEATURE_FANCY_TAIL(
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38 | //usage: "\n -c N[kbm] Print last N bytes"
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39 | //usage: "\n -q Never print headers"
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40 | //usage: "\n -v Always print headers"
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41 | //usage: "\n"
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42 | //usage: "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
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43 | //usage: "\nIf N starts with a '+', output begins with the Nth item from the start"
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44 | //usage: "\nof each file, not from the end."
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45 | //usage: )
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46 | //usage:
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47 | //usage:#define tail_example_usage
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48 | //usage: "$ tail -n 1 /etc/resolv.conf\n"
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49 | //usage: "nameserver 10.0.0.1\n"
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50 |
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51 | #include "libbb.h"
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52 |
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53 | static const struct suffix_mult tail_suffixes[] = {
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54 | { "b", 512 },
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55 | { "k", 1024 },
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56 | { "m", 1024*1024 },
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57 | { "", 0 }
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58 | };
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59 |
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60 | struct globals {
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61 | bool from_top;
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62 | bool exitcode;
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63 | } FIX_ALIASING;
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64 | #define G (*(struct globals*)&bb_common_bufsiz1)
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65 | #define INIT_G() do { } while (0)
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66 |
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67 | static void tail_xprint_header(const char *fmt, const char *filename)
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68 | {
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69 | if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
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70 | bb_perror_nomsg_and_die();
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71 | }
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72 |
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73 | static ssize_t tail_read(int fd, char *buf, size_t count)
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74 | {
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75 | ssize_t r;
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76 | off_t current;
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77 | struct stat sbuf;
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78 |
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79 | /* /proc files report zero st_size, don't lseek them. */
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80 | if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
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81 | current = lseek(fd, 0, SEEK_CUR);
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82 | if (sbuf.st_size < current)
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83 | xlseek(fd, 0, SEEK_SET);
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84 | }
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85 |
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86 | r = full_read(fd, buf, count);
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87 | if (r < 0) {
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88 | bb_perror_msg(bb_msg_read_error);
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89 | G.exitcode = EXIT_FAILURE;
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90 | }
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91 |
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92 | return r;
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93 | }
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94 |
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95 | #define header_fmt_str "\n==> %s <==\n"
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96 |
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97 | static unsigned eat_num(const char *p)
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98 | {
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99 | if (*p == '-')
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100 | p++;
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101 | else if (*p == '+') {
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102 | p++;
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103 | G.from_top = 1;
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104 | }
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105 | return xatou_sfx(p, tail_suffixes);
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106 | }
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107 |
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108 | int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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109 | int tail_main(int argc, char **argv)
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110 | {
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111 | unsigned count = 10;
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112 | unsigned sleep_period = 1;
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113 | const char *str_c, *str_n;
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114 |
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115 | char *tailbuf;
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116 | size_t tailbufsize;
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117 | unsigned header_threshhold = 1;
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118 | unsigned nfiles;
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119 | int i, opt;
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120 |
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121 | int *fds;
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122 | const char *fmt;
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123 |
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124 | INIT_G();
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125 |
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126 | #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
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127 | /* Allow legacy syntax of an initial numeric option without -n. */
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128 | if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
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129 | && isdigit(argv[1][1])
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130 | ) {
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131 | count = eat_num(argv[1]);
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132 | argv++;
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133 | argc--;
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134 | }
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135 | #endif
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136 |
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137 | /* -s NUM, -F imlies -f */
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138 | IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
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139 | opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
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140 | &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
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141 | #define FOLLOW (opt & 0x1)
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142 | #define COUNT_BYTES (opt & 0x2)
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143 | //if (opt & 0x1) // -f
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144 | if (opt & 0x2) count = eat_num(str_c); // -c
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145 | if (opt & 0x4) count = eat_num(str_n); // -n
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146 | #if ENABLE_FEATURE_FANCY_TAIL
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147 | /* q: make it impossible for nfiles to be > header_threshhold */
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148 | if (opt & 0x8) header_threshhold = UINT_MAX; // -q
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149 | //if (opt & 0x10) // -s
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150 | if (opt & 0x20) header_threshhold = 0; // -v
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151 | # define FOLLOW_RETRY (opt & 0x40)
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152 | #else
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153 | # define FOLLOW_RETRY 0
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154 | #endif
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155 | argc -= optind;
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156 | argv += optind;
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157 |
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158 | /* open all the files */
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159 | fds = xmalloc(sizeof(fds[0]) * (argc + 1));
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160 | if (!argv[0]) {
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161 | struct stat statbuf;
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162 |
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163 | if (fstat(STDIN_FILENO, &statbuf) == 0
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164 | && S_ISFIFO(statbuf.st_mode)
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165 | ) {
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166 | opt &= ~1; /* clear FOLLOW */
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167 | }
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168 | argv[0] = (char *) bb_msg_standard_input;
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169 | }
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170 | nfiles = i = 0;
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171 | do {
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172 | int fd = open_or_warn_stdin(argv[i]);
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173 | if (fd < 0 && !FOLLOW_RETRY) {
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174 | G.exitcode = EXIT_FAILURE;
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175 | continue;
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176 | }
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177 | fds[nfiles] = fd;
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178 | argv[nfiles++] = argv[i];
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179 | } while (++i < argc);
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180 |
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181 | if (!nfiles)
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182 | bb_error_msg_and_die("no files");
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183 |
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184 | /* prepare the buffer */
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185 | tailbufsize = BUFSIZ;
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186 | if (!G.from_top && COUNT_BYTES) {
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187 | if (tailbufsize < count + BUFSIZ) {
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188 | tailbufsize = count + BUFSIZ;
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189 | }
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190 | }
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191 | /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
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192 | * (In fact, it doesn't need ANY memory). So delay allocation.
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193 | */
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194 | tailbuf = NULL;
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195 |
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196 | /* tail the files */
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197 |
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198 | fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
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199 | i = 0;
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200 | do {
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201 | char *buf;
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202 | int taillen;
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203 | int newlines_seen;
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204 | unsigned seen;
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205 | int nread;
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206 | int fd = fds[i];
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207 |
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208 | if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
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209 | continue; /* may happen with -F */
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210 |
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211 | if (nfiles > header_threshhold) {
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212 | tail_xprint_header(fmt, argv[i]);
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213 | fmt = header_fmt_str;
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214 | }
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215 |
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216 | if (!G.from_top) {
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217 | off_t current = lseek(fd, 0, SEEK_END);
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218 | if (current > 0) {
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219 | unsigned off;
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220 | if (COUNT_BYTES) {
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221 | /* Optimizing count-bytes case if the file is seekable.
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222 | * Beware of backing up too far.
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223 | * Also we exclude files with size 0 (because of /proc/xxx) */
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224 | if (count == 0)
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225 | continue; /* showing zero bytes is easy :) */
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226 | current -= count;
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227 | if (current < 0)
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228 | current = 0;
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229 | xlseek(fd, current, SEEK_SET);
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230 | bb_copyfd_size(fd, STDOUT_FILENO, count);
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231 | continue;
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232 | }
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233 | #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
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234 | /* Optimizing count-lines case if the file is seekable.
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235 | * We assume the lines are <64k.
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236 | * (Users complain that tail takes too long
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237 | * on multi-gigabyte files) */
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238 | off = (count | 0xf); /* for small counts, be more paranoid */
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239 | if (off > (INT_MAX / (64*1024)))
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240 | off = (INT_MAX / (64*1024));
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241 | current -= off * (64*1024);
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242 | if (current < 0)
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243 | current = 0;
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244 | xlseek(fd, current, SEEK_SET);
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245 | #endif
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246 | }
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247 | }
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248 |
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249 | if (!tailbuf)
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250 | tailbuf = xmalloc(tailbufsize);
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251 |
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252 | buf = tailbuf;
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253 | taillen = 0;
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254 | /* "We saw 1st line/byte".
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255 | * Used only by +N code ("start from Nth", 1-based): */
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256 | seen = 1;
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257 | newlines_seen = 0;
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258 | while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
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259 | if (G.from_top) {
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260 | int nwrite = nread;
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261 | if (seen < count) {
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262 | /* We need to skip a few more bytes/lines */
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263 | if (COUNT_BYTES) {
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264 | nwrite -= (count - seen);
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265 | seen += nread;
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266 | } else {
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267 | char *s = buf;
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268 | do {
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269 | --nwrite;
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270 | if (*s++ == '\n' && ++seen == count) {
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271 | break;
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272 | }
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273 | } while (nwrite);
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274 | }
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275 | }
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276 | if (nwrite > 0)
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277 | xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
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278 | } else if (count) {
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279 | if (COUNT_BYTES) {
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280 | taillen += nread;
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281 | if (taillen > (int)count) {
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282 | memmove(tailbuf, tailbuf + taillen - count, count);
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283 | taillen = count;
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284 | }
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285 | } else {
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286 | int k = nread;
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287 | int newlines_in_buf = 0;
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288 |
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289 | do { /* count '\n' in last read */
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290 | k--;
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291 | if (buf[k] == '\n') {
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292 | newlines_in_buf++;
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293 | }
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294 | } while (k);
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295 |
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296 | if (newlines_seen + newlines_in_buf < (int)count) {
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297 | newlines_seen += newlines_in_buf;
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298 | taillen += nread;
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299 | } else {
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300 | int extra = (buf[nread-1] != '\n');
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301 | char *s;
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302 |
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303 | k = newlines_seen + newlines_in_buf + extra - count;
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304 | s = tailbuf;
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305 | while (k) {
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306 | if (*s == '\n') {
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307 | k--;
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308 | }
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309 | s++;
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310 | }
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311 | taillen += nread - (s - tailbuf);
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312 | memmove(tailbuf, s, taillen);
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313 | newlines_seen = count - extra;
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314 | }
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315 | if (tailbufsize < (size_t)taillen + BUFSIZ) {
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316 | tailbufsize = taillen + BUFSIZ;
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317 | tailbuf = xrealloc(tailbuf, tailbufsize);
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318 | }
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319 | }
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320 | buf = tailbuf + taillen;
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321 | }
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322 | } /* while (tail_read() > 0) */
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323 | if (!G.from_top) {
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324 | xwrite(STDOUT_FILENO, tailbuf, taillen);
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325 | }
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326 | } while (++i < nfiles);
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327 |
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328 | tailbuf = xrealloc(tailbuf, BUFSIZ);
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329 |
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330 | fmt = NULL;
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331 |
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332 | if (FOLLOW) while (1) {
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333 | sleep(sleep_period);
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334 |
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335 | i = 0;
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336 | do {
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337 | int nread;
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338 | const char *filename = argv[i];
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339 | int fd = fds[i];
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340 |
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341 | if (FOLLOW_RETRY) {
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342 | struct stat sbuf, fsbuf;
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343 |
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344 | if (fd < 0
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345 | || fstat(fd, &fsbuf) < 0
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346 | || stat(filename, &sbuf) < 0
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347 | || fsbuf.st_dev != sbuf.st_dev
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348 | || fsbuf.st_ino != sbuf.st_ino
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349 | ) {
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350 | int new_fd;
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351 |
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352 | if (fd >= 0)
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353 | close(fd);
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354 | new_fd = open(filename, O_RDONLY);
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355 | if (new_fd >= 0) {
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356 | bb_error_msg("%s has %s; following end of new file",
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357 | filename, (fd < 0) ? "appeared" : "been replaced"
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358 | );
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359 | } else if (fd >= 0) {
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360 | bb_perror_msg("%s has become inaccessible", filename);
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361 | }
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362 | fds[i] = fd = new_fd;
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363 | }
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364 | }
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365 | if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
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366 | continue;
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367 | if (nfiles > header_threshhold) {
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368 | fmt = header_fmt_str;
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369 | }
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370 | while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
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371 | if (fmt) {
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372 | tail_xprint_header(fmt, filename);
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373 | fmt = NULL;
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374 | }
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375 | xwrite(STDOUT_FILENO, tailbuf, nread);
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376 | }
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377 | } while (++i < nfiles);
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378 | } /* while (1) */
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379 |
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380 | if (ENABLE_FEATURE_CLEAN_UP) {
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381 | free(fds);
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382 | free(tailbuf);
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383 | }
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384 | return G.exitcode;
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385 | }
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