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1 /* vi: set sw=4 ts=4:
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2 *
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3 * tail.c - copy last lines from input to stdout.
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4 *
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5 * Copyright 2012 Timothy Elliott <tle@holymonkey.com>
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6 *
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7 * See http://www.opengroup.org/onlinepubs/009695399/utilities/tail.html
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8
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9 USE_HEAD(NEWTOY(tail, "c:fn:", TOYFLAG_BIN))
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10
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11 config TAIL
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12 bool "tail"
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13 default n
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14 help
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15 usage: tail [-n number] [-c number] [-f] [file...]
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16
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17 Copy last lines from files to stdout. If no files listed, copy from
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18 stdin. Filename "-" is a synonym for stdin.
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19
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20 -n Line offset to start copying from. The number may be signed.
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21 When negative, the line offset is counted from the end of the
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22 file. When positive, the offset is counted from the beginning.
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23 When the sign is omitted, the offset is counted from the end of
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24 the file. Defaults to -10.
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25
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26 -c Byte offset to start copying from. As above, may be a positive
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27 or negative signed number.
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28
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29 -f Continue reading input after reaching the last line of input.
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30 This option is ignored if the input file is not a regular file
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31 or the given file is a FIFO.
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32 */
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33
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34 #include "toys.h"
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35
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36 DEFINE_GLOBALS(
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37 char *lines_str;
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38 char *bytes_str;
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39 long lines;
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40 long bytes;
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41 int file_no;
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42 )
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43
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44 #define TT this.tail
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45
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46 #define FLAG_n 1
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47 #define FLAG_f 2
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48 #define FLAG_c 4
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49
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50 struct line_list {
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51 struct line_list *next;
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52 char *data;
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53 ssize_t len;
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54 long lines;
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55 };
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56
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57 static void print_after_offset(int fd, long bytes, long lines)
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58 {
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59 ssize_t read_len;
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60 long size=sizeof(toybuf);
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61 char c;
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62
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63 while (bytes > 0 || lines > 0) {
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64 if (1>read(fd, &c, 1)) break;
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65 bytes--;
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66 if (c == '\n') lines--;
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67 }
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68
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69 for (;;) {
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70 read_len = xread(fd, toybuf, size);
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71 if (read_len<1) break;
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72 xwrite(1, toybuf, read_len);
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73 }
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74 }
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75
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76 static void print_last_bytes(int fd, long bytes)
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77 {
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78 char *buf1, *buf2, *temp;
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79 ssize_t read_len;
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80
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81 buf1 = xmalloc(bytes);
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82 buf2 = xmalloc(bytes);
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83
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84 for(;;) {
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85 // swap buf1 and buf2
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86 temp = buf1;
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87 buf1 = buf2;
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88 buf2 = temp;
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89
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90 read_len = readall(fd, buf2, bytes);
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91 if (read_len<bytes) break;
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92 }
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93
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94 // output part of buf1 and all of buf2
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95 xwrite(1, buf1 + read_len, bytes - read_len);
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96 xwrite(1, buf2, read_len);
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97
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98 if (CFG_TOYBOX_FREE) {
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99 free(buf1);
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100 free(buf2);
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101 }
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102 }
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103
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104 static void free_line(void *data)
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105 {
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106 struct line_list *list = (struct line_list *)data;
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107 free(list->data);
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108 free(list);
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109 }
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110
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111 static void llist_add(struct line_list **head, struct line_list *new)
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112 {
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113 struct line_list *cur = *head;
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114
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115 new->next = NULL;
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116 if (cur) {
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117 while (cur->next)
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118 cur = cur->next;
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119 cur->next = new;
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120 } else *head = new;
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121 }
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122
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123 static void print_last_lines(int fd, long lines)
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124 {
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125 ssize_t i, total=0;
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126 long size=sizeof(toybuf);
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127 struct line_list *buf=NULL, *cur;
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128
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129 for (;;) {
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130 // read from input and append to buffer list
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131 cur = xmalloc(sizeof(struct line_list));
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132 memset(cur, 0, sizeof(struct line_list));
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133
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134 cur->data = xmalloc(size);
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135 cur->len = readall(fd, cur->data, size);
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136 llist_add(&buf, cur);
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137
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138 // count newlines in latest input
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139 for (i=0; i<cur->len; i++)
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140 if (cur->data[i] == '\n') cur->lines++;
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141 total += cur->lines;
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142
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143 // release first buffers if it leaves us enough newlines
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144 while (total - buf->lines > lines) {
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145 total -= buf->lines;
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146 free_line(llist_pop(&buf));
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147 }
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148 if (cur->len < size) break;
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149 }
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150
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151 // if last buffer doesn't end in a newline, pretend like it did
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152 if (cur->data[cur->len - 1]!='\n') total++;
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153
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154 // print out part of the first buffer
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155 i = 0;
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156 while (total>lines)
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157 if (buf->data[i++]=='\n') total--;
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158 xwrite(1, buf->data + i, buf->len - i);
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159
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160 // print remaining buffers in their entirety
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161 for (cur=buf->next; cur; cur=cur->next)
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162 xwrite(1, cur->data, cur->len);
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163
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164 if (CFG_TOYBOX_FREE) llist_free(buf, free_line);
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165 }
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166
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167 static void do_tail(int fd, char *name)
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168 {
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169 long lines=TT.lines, bytes=TT.bytes;
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170
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171 if (toys.optc > 1) {
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172 // print an extra newline for all but the first file
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173 if (TT.file_no++) xprintf("\n");
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174 xprintf("==> %s <==\n", name);
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175 xflush();
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176 }
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177
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178 if (lines > 0 || bytes > 0) print_after_offset(fd, bytes, lines);
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179 else if (bytes < 0) print_last_bytes(fd, bytes * -1);
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180 else if (lines < 0) print_last_lines(fd, lines * -1);
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181 }
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182
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183 long atolx_default_negative(char *str)
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184 {
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185 long val = atolx(str);
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186 return str[0] != '+' && str[0] != '-' ? val * -1 : val;
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187 }
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188
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189 void tail_main(void)
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190 {
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191 // if option -c or -n has no sign then we make it negative
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192 if (toys.optflags & FLAG_c)
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193 TT.bytes = atolx_default_negative(TT.bytes_str);
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194
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195 if (toys.optflags & FLAG_n)
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196 TT.lines = atolx_default_negative(TT.lines_str);
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197 else
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198 TT.lines = -10;
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199
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200 loopfiles(toys.optargs, do_tail);
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201 }
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