1 00:00:00,720 --> 00:00:01,740 In this lesson, 2 00:00:01,740 --> 00:00:04,410 we're going to discuss the processing of text files 3 00:00:04,410 --> 00:00:06,570 by using a number of command line tools 4 00:00:06,570 --> 00:00:08,850 to perform operations on text files 5 00:00:08,850 --> 00:00:11,910 and then write those results to the standard output. 6 00:00:11,910 --> 00:00:13,260 By the end of this video, 7 00:00:13,260 --> 00:00:15,630 you're going to be expected to process information 8 00:00:15,630 --> 00:00:16,980 in powerful ways 9 00:00:16,980 --> 00:00:20,460 by restructuring output to generate useful reports, 10 00:00:20,460 --> 00:00:22,350 modifying text in the files, 11 00:00:22,350 --> 00:00:25,200 and many other system administration tasks. 12 00:00:25,200 --> 00:00:26,033 To do this, 13 00:00:26,033 --> 00:00:28,500 we're first going to talk about the echo command. 14 00:00:28,500 --> 00:00:31,050 The echo command is a built-in Linux feature 15 00:00:31,050 --> 00:00:34,170 that prints out arguments as the standard output. 16 00:00:34,170 --> 00:00:36,000 The echo command is commonly used 17 00:00:36,000 --> 00:00:38,160 to display text strings or command results 18 00:00:38,160 --> 00:00:40,200 as messages to the screen. 19 00:00:40,200 --> 00:00:41,280 To run echo, 20 00:00:41,280 --> 00:00:43,830 you simply type in echo and a string. 21 00:00:43,830 --> 00:00:45,690 For example, let's say I typed in 22 00:00:45,690 --> 00:00:47,460 echo "Hello, World!" 23 00:00:47,460 --> 00:00:49,200 The output that's going to be printed to the screen 24 00:00:49,200 --> 00:00:50,940 is Hello, World! 25 00:00:50,940 --> 00:00:52,890 So that means using the echo command 26 00:00:52,890 --> 00:00:55,200 returns the provided string as the output 27 00:00:55,200 --> 00:00:57,510 with absolutely no changes. 28 00:00:57,510 --> 00:00:59,940 The printf command is similar to echo 29 00:00:59,940 --> 00:01:02,580 but it provides the user with a lot more control 30 00:01:02,580 --> 00:01:05,069 over how the output is going to be formatted. 31 00:01:05,069 --> 00:01:07,170 You can supply various format characters 32 00:01:07,170 --> 00:01:08,820 within the text you want to output 33 00:01:08,820 --> 00:01:10,650 by using things like the backslash 34 00:01:10,650 --> 00:01:12,810 to indicate where they're going to be used. 35 00:01:12,810 --> 00:01:13,710 For example, 36 00:01:13,710 --> 00:01:18,710 if I type printf "Hello.\nWhat's your name?", 37 00:01:21,090 --> 00:01:23,400 this will print Hello. What's your name? 38 00:01:23,400 --> 00:01:26,670 because that \n is a new line format character. 39 00:01:26,670 --> 00:01:28,650 It's automatically going to add a new line 40 00:01:28,650 --> 00:01:29,850 wherever it's placed, 41 00:01:29,850 --> 00:01:32,520 in this case after the hello. 42 00:01:32,520 --> 00:01:34,260 Whenever you need to perform operations 43 00:01:34,260 --> 00:01:36,120 like removing repeated characters, 44 00:01:36,120 --> 00:01:38,040 converting uppercase to lowercase, 45 00:01:38,040 --> 00:01:40,470 and basic character replacing and removing, 46 00:01:40,470 --> 00:01:43,110 you might want to look at the tr command. 47 00:01:43,110 --> 00:01:44,580 The tr command can be run 48 00:01:44,580 --> 00:01:47,040 by typing tr, the first character, 49 00:01:47,040 --> 00:01:48,690 and then the second character. 50 00:01:48,690 --> 00:01:50,190 This is where the first character 51 00:01:50,190 --> 00:01:52,140 is the character you want to replace. 52 00:01:52,140 --> 00:01:55,740 So for example, let's say I typed in linuxize, 53 00:01:55,740 --> 00:01:58,290 L-I-N-U-X-I-Z-E, 54 00:01:58,290 --> 00:02:01,080 and then I pipe that over to the tr command, 55 00:02:01,080 --> 00:02:03,420 and I want to remove l,i,n 56 00:02:03,420 --> 00:02:06,030 and replace it with r,e,d. 57 00:02:06,030 --> 00:02:08,130 Each time I see an occurrence of L, 58 00:02:08,130 --> 00:02:10,199 it's going to be replace with the R, 59 00:02:10,199 --> 00:02:11,460 every time I see an I, 60 00:02:11,460 --> 00:02:13,020 it's going to replace with an E, 61 00:02:13,020 --> 00:02:14,490 every time I see that N, 62 00:02:14,490 --> 00:02:16,080 it's going to be replace with a D, 63 00:02:16,080 --> 00:02:17,700 so I'm replacing those three characters 64 00:02:17,700 --> 00:02:19,800 with the r,e,d characters. 65 00:02:19,800 --> 00:02:24,510 This will give me the output of R-E-D-U-X-E-Z-E. 66 00:02:24,510 --> 00:02:26,340 So now instead of linuxize, 67 00:02:26,340 --> 00:02:28,800 I'm getting reduxeze. 68 00:02:28,800 --> 00:02:31,980 Another command we can use is known as wc. 69 00:02:31,980 --> 00:02:34,920 wc is going to allow you to count the number of lines 70 00:02:34,920 --> 00:02:36,390 the words, the characters, 71 00:02:36,390 --> 00:02:39,690 and the bites of any given file or standard input, 72 00:02:39,690 --> 00:02:41,490 and then print the result out. 73 00:02:41,490 --> 00:02:43,410 If multiple files are specified, 74 00:02:43,410 --> 00:02:45,630 the command will display the counts for each file 75 00:02:45,630 --> 00:02:48,150 and the total count for all of the files. 76 00:02:48,150 --> 00:02:49,080 To run this, 77 00:02:49,080 --> 00:02:53,010 simply type in wc, the options, and the file names. 78 00:02:53,010 --> 00:02:55,380 Now, there is a lot of different options you can use 79 00:02:55,380 --> 00:02:57,450 within the wc command. 80 00:02:57,450 --> 00:02:58,320 For example, 81 00:02:58,320 --> 00:03:01,560 you can -c if you want to display the byte count, 82 00:03:01,560 --> 00:03:02,820 if you use -m, 83 00:03:02,820 --> 00:03:04,890 it's going to display the character count, 84 00:03:04,890 --> 00:03:06,240 if you do -l, 85 00:03:06,240 --> 00:03:08,220 it's going to display the new line count, 86 00:03:08,220 --> 00:03:09,750 and if you do -w, 87 00:03:09,750 --> 00:03:12,000 it's going to display the word count. 88 00:03:12,000 --> 00:03:14,550 Another command we have is known as sort. 89 00:03:14,550 --> 00:03:16,920 The sort command is a command line utility 90 00:03:16,920 --> 00:03:19,260 for sorting lines of text files. 91 00:03:19,260 --> 00:03:22,140 The sort command supports sorting alphabetically, 92 00:03:22,140 --> 00:03:23,400 in reverse order, 93 00:03:23,400 --> 00:03:25,230 by number, by month, 94 00:03:25,230 --> 00:03:27,720 and it can also remove duplicates for you. 95 00:03:27,720 --> 00:03:29,850 There are a few options for the sort command 96 00:03:29,850 --> 00:03:31,140 you should be familiar with 97 00:03:31,140 --> 00:03:34,230 including the -k option and the column number. 98 00:03:34,230 --> 00:03:35,220 When you do this, 99 00:03:35,220 --> 00:03:38,580 it's going to specify the field value that you want to use. 100 00:03:38,580 --> 00:03:40,500 So if I use -k2, 101 00:03:40,500 --> 00:03:42,870 this indicates the second field. 102 00:03:42,870 --> 00:03:44,820 If you use the -n option, 103 00:03:44,820 --> 00:03:46,500 this compare and sorts lines 104 00:03:46,500 --> 00:03:48,960 based on a string's numerical value, 105 00:03:48,960 --> 00:03:50,610 if you use the -r option, 106 00:03:50,610 --> 00:03:53,040 it's going to sort the fields in descending order 107 00:03:53,040 --> 00:03:54,480 because the fields are going to be sorted 108 00:03:54,480 --> 00:03:56,220 in ascending order by default, 109 00:03:56,220 --> 00:03:57,510 and so by using -r, 110 00:03:57,510 --> 00:03:59,310 we're going to reverse that. 111 00:03:59,310 --> 00:04:01,740 Another option you can use is -t, 112 00:04:01,740 --> 00:04:04,770 which allows you to separate one field from another. 113 00:04:04,770 --> 00:04:06,120 To run the sort command, 114 00:04:06,120 --> 00:04:10,080 simply type in sort, your options, and your file name. 115 00:04:10,080 --> 00:04:13,080 Another command we need to talk about is the cut command. 116 00:04:13,080 --> 00:04:16,140 The cut command extracts specific lines of text 117 00:04:16,140 --> 00:04:17,519 from a file. 118 00:04:17,519 --> 00:04:20,610 Common cut command options include -c. 119 00:04:20,610 --> 00:04:22,590 The -c option is going to specify 120 00:04:22,590 --> 00:04:25,680 the number of characters to cut from each line. 121 00:04:25,680 --> 00:04:28,110 If you use the -d and a delimiter, 122 00:04:28,110 --> 00:04:30,240 it's going to separate one field from another 123 00:04:30,240 --> 00:04:31,590 by using that delimiter. 124 00:04:31,590 --> 00:04:34,980 For instance, a comma for comma-separated values. 125 00:04:34,980 --> 00:04:37,290 If you use -f and the field number, 126 00:04:37,290 --> 00:04:39,600 this is going to specify the field numbers to cut 127 00:04:39,600 --> 00:04:41,490 as separated by the delimiter. 128 00:04:41,490 --> 00:04:44,670 For example, -f2 will indicate the field 129 00:04:44,670 --> 00:04:47,970 between the first and second instances of the delimiter 130 00:04:47,970 --> 00:04:51,300 or those commas in a comma-separated value file. 131 00:04:51,300 --> 00:04:52,133 And finally, 132 00:04:52,133 --> 00:04:55,470 s is an option we can use to suppress a line 133 00:04:55,470 --> 00:04:57,780 if a delimiter is not found. 134 00:04:57,780 --> 00:04:59,070 To run the cut command, 135 00:04:59,070 --> 00:05:02,760 simply type in cut, the options, and the file name. 136 00:05:02,760 --> 00:05:05,100 Another one we have is the paste command. 137 00:05:05,100 --> 00:05:07,110 The paste command is used to merge lines 138 00:05:07,110 --> 00:05:09,240 from text files horizontally, 139 00:05:09,240 --> 00:05:11,460 each line of an initial file in a row 140 00:05:11,460 --> 00:05:13,170 is going to be in the first column. 141 00:05:13,170 --> 00:05:16,290 In using paste, you specify a second file, 142 00:05:16,290 --> 00:05:18,030 and every line of the second file 143 00:05:18,030 --> 00:05:20,820 becomes a row in a new second column. 144 00:05:20,820 --> 00:05:21,720 By default, 145 00:05:21,720 --> 00:05:24,780 the paste command uses a tab space deliminator 146 00:05:24,780 --> 00:05:26,550 to separate each column. 147 00:05:26,550 --> 00:05:29,010 So you can use the -d option 148 00:05:29,010 --> 00:05:30,780 to specify a different deliminator, 149 00:05:30,780 --> 00:05:32,490 like a comma if you wanted to, 150 00:05:32,490 --> 00:05:35,280 but by default, it is going to use a tab. 151 00:05:35,280 --> 00:05:37,920 So, for example, let's say I have two files: 152 00:05:37,920 --> 00:05:40,050 the first file is a name of cities 153 00:05:40,050 --> 00:05:44,340 and I have New York, Tokyo, London, and Lima in it, 154 00:05:44,340 --> 00:05:46,740 then I have another file called countries 155 00:05:46,740 --> 00:05:51,030 and it has United States, Japan, England, and Peru. 156 00:05:51,030 --> 00:05:54,690 So if I wanted to combine those two files into one list, 157 00:05:54,690 --> 00:05:57,390 I could do that by running the paste command. 158 00:05:57,390 --> 00:06:02,130 I would type paste -d , cities countries, 159 00:06:02,130 --> 00:06:03,270 and hit Enter. 160 00:06:03,270 --> 00:06:04,830 This then creates the output 161 00:06:04,830 --> 00:06:07,020 of New York, United States; 162 00:06:07,020 --> 00:06:08,730 Tokyo, Japan; 163 00:06:08,730 --> 00:06:10,200 London, England; 164 00:06:10,200 --> 00:06:11,760 and Lima, Peru 165 00:06:11,760 --> 00:06:13,740 because I'm using that comma I specified 166 00:06:13,740 --> 00:06:15,510 as my delineator. 167 00:06:15,510 --> 00:06:18,420 Another command for us to look at is the diff command. 168 00:06:18,420 --> 00:06:21,330 Now the diff command is used to compare text files 169 00:06:21,330 --> 00:06:23,820 and it's going to find the difference between them. 170 00:06:23,820 --> 00:06:25,920 This command is going to display the two files 171 00:06:25,920 --> 00:06:27,510 and the differences between them. 172 00:06:27,510 --> 00:06:30,120 It's really useful when you're trying to do version control 173 00:06:30,120 --> 00:06:32,190 across different code bases. 174 00:06:32,190 --> 00:06:33,900 If you're using various symbols, 175 00:06:33,900 --> 00:06:35,220 the output can actually suggest 176 00:06:35,220 --> 00:06:37,440 how you can change one file to another 177 00:06:37,440 --> 00:06:39,540 to make it identical to each other. 178 00:06:39,540 --> 00:06:41,880 Each symbol now has a special meaning. 179 00:06:41,880 --> 00:06:44,610 If you have a less than symbol with a line after it, 180 00:06:44,610 --> 00:06:47,460 this means the line should be removed from the first file 181 00:06:47,460 --> 00:06:50,010 because it doesn't appear in the second file. 182 00:06:50,010 --> 00:06:52,830 If you have a greater than symbol with the line after it, 183 00:06:52,830 --> 00:06:55,560 this means that line should be added to the second file 184 00:06:55,560 --> 00:06:57,480 because it doesn't exist there. 185 00:06:57,480 --> 00:06:58,710 In addition to this, 186 00:06:58,710 --> 00:07:01,170 the diff command can also denote the line numbers 187 00:07:01,170 --> 00:07:02,670 for each line in the file 188 00:07:02,670 --> 00:07:04,950 that would be affected by the deletion, addition, 189 00:07:04,950 --> 00:07:06,840 or change operations. 190 00:07:06,840 --> 00:07:08,250 To run the diff command, 191 00:07:08,250 --> 00:07:11,970 type diff, file name 1 and file name 2. 192 00:07:11,970 --> 00:07:14,250 Now the diff command also has some various options 193 00:07:14,250 --> 00:07:15,676 that we're going to talk about: 194 00:07:15,676 --> 00:07:19,352 b is the option that ignores spacing differences, 195 00:07:19,352 --> 00:07:22,246 i ignores case differences, 196 00:07:22,246 --> 00:07:26,477 t is going to expand tab characters in the output files, 197 00:07:26,477 --> 00:07:30,378 w is going to ignore spacing differences in tabs, 198 00:07:30,378 --> 00:07:33,780 c is going to display a list of all the differences 199 00:07:33,780 --> 00:07:35,670 with three lines of context, 200 00:07:35,670 --> 00:07:39,330 while -u is going to output the results in a unified mode, 201 00:07:39,330 --> 00:07:42,060 which presents a more streamlined format. 202 00:07:42,060 --> 00:07:43,920 The next command we're going to talk about is grep, 203 00:07:43,920 --> 00:07:47,880 and grep in its most basic form is a search tool. 204 00:07:47,880 --> 00:07:49,650 But unlike find or locate, 205 00:07:49,650 --> 00:07:52,470 it's not limited to finding file names. 206 00:07:52,470 --> 00:07:56,310 Instead, it's often used to search the contents of the file 207 00:07:56,310 --> 00:07:58,470 for a particular string of text 208 00:07:58,470 --> 00:07:59,400 By default, 209 00:07:59,400 --> 00:08:02,160 grep is going to display each full line of the file 210 00:08:02,160 --> 00:08:04,740 that your search pattern is found inside of. 211 00:08:04,740 --> 00:08:05,760 In this way, 212 00:08:05,760 --> 00:08:08,460 you can use grep to both process a text file 213 00:08:08,460 --> 00:08:11,370 and read the contents that are most pertinent to you, 214 00:08:11,370 --> 00:08:14,160 and we use grep a lot in the cybersecurity world 215 00:08:14,160 --> 00:08:15,630 when we're looking through log files 216 00:08:15,630 --> 00:08:18,450 and trying to find specific instances of things. 217 00:08:18,450 --> 00:08:19,380 For example, 218 00:08:19,380 --> 00:08:21,690 you may want to audit the user's login events 219 00:08:21,690 --> 00:08:23,550 by looking at an access log. 220 00:08:23,550 --> 00:08:25,320 Instead of reading the entire log 221 00:08:25,320 --> 00:08:27,900 and stepping through a search term in a text editor, 222 00:08:27,900 --> 00:08:29,190 you can instead simply print 223 00:08:29,190 --> 00:08:31,110 all the relevant lines to the screen 224 00:08:31,110 --> 00:08:32,970 by using the grep command. 225 00:08:32,970 --> 00:08:34,860 The proper way to use the grep command 226 00:08:34,860 --> 00:08:38,010 is to type in grep, the options, the search pattern, 227 00:08:38,010 --> 00:08:39,450 and the file name. 228 00:08:39,450 --> 00:08:41,190 The grep command has a couple of options 229 00:08:41,190 --> 00:08:42,390 we need to talk about, 230 00:08:42,390 --> 00:08:45,990 the first one is -E and a pattern. 231 00:08:45,990 --> 00:08:48,150 This is used to use pattern matching 232 00:08:48,150 --> 00:08:50,340 using an extended regular expression 233 00:08:50,340 --> 00:08:52,920 instead of just using a standard search term. 234 00:08:52,920 --> 00:08:55,410 If you use -F in a pattern, 235 00:08:55,410 --> 00:08:56,700 this is used to match a pattern 236 00:08:56,700 --> 00:08:58,890 as a list of fixed strings. 237 00:08:58,890 --> 00:09:01,320 The option -f and a file name 238 00:09:01,320 --> 00:09:02,700 will be used to match patterns 239 00:09:02,700 --> 00:09:05,340 that are contained in a specified file. 240 00:09:05,340 --> 00:09:08,850 The option -i is going to be used to ignore casing, 241 00:09:08,850 --> 00:09:11,730 and the option -v is used to output lines 242 00:09:11,730 --> 00:09:15,090 only if those lines don't match the provided pattern, 243 00:09:15,090 --> 00:09:15,923 so essentially, 244 00:09:15,923 --> 00:09:17,340 show me everything that doesn't match 245 00:09:17,340 --> 00:09:18,810 what I'm looking for. 246 00:09:18,810 --> 00:09:21,300 The option -c is going to be used to print 247 00:09:21,300 --> 00:09:23,520 only the numbers of the matching lines 248 00:09:23,520 --> 00:09:25,800 and not the actual lines themself, 249 00:09:25,800 --> 00:09:28,830 and the option -l is going to print only the files 250 00:09:28,830 --> 00:09:30,330 that have matching lines, 251 00:09:30,330 --> 00:09:32,130 not the lines themself. 252 00:09:32,130 --> 00:09:33,750 This is helpful if you're trying to find 253 00:09:33,750 --> 00:09:37,350 is there this keyword across all the files on my system 254 00:09:37,350 --> 00:09:39,840 and it'll tell you all the files that match that keyword 255 00:09:39,840 --> 00:09:41,280 inside of them, 256 00:09:41,280 --> 00:09:43,500 and the option -o is going to print 257 00:09:43,500 --> 00:09:45,240 only the matching part of a line 258 00:09:45,240 --> 00:09:47,280 instead of the entire line. 259 00:09:47,280 --> 00:09:49,860 Now, in addition to searching the contents of the files, 260 00:09:49,860 --> 00:09:52,260 you can also use grep to search a directory 261 00:09:52,260 --> 00:09:54,000 in order to locate a certain file 262 00:09:54,000 --> 00:09:56,640 that contains those keywords or patterns. 263 00:09:56,640 --> 00:09:58,950 For example, if I wanted to find files 264 00:09:58,950 --> 00:10:00,870 with the keyword audit in them, 265 00:10:00,870 --> 00:10:03,420 I can use the ls -l command 266 00:10:03,420 --> 00:10:06,780 and then pipe that into grep with the word audit. 267 00:10:06,780 --> 00:10:09,300 This would return a long listing of any files 268 00:10:09,300 --> 00:10:10,530 in the current directory 269 00:10:10,530 --> 00:10:13,050 whose name contains audit. 270 00:10:13,050 --> 00:10:14,610 The next command we're going to talk about 271 00:10:14,610 --> 00:10:16,770 is the awk command. 272 00:10:16,770 --> 00:10:20,670 The awk command performs pattern matching on files. 273 00:10:20,670 --> 00:10:23,970 It's based on the AWK programming language. 274 00:10:23,970 --> 00:10:27,390 The awk keyword is going to be followed by the pattern, 275 00:10:27,390 --> 00:10:28,710 the action to be performed, 276 00:10:28,710 --> 00:10:30,150 and the file name. 277 00:10:30,150 --> 00:10:31,620 Now, the action to be performed 278 00:10:31,620 --> 00:10:33,600 is given within curly braces, 279 00:10:33,600 --> 00:10:35,730 and the pattern and the action to be performed 280 00:10:35,730 --> 00:10:38,640 should be specified within a single quote. 281 00:10:38,640 --> 00:10:40,500 If the pattern is not specified, 282 00:10:40,500 --> 00:10:43,170 the action is performed on all input data. 283 00:10:43,170 --> 00:10:45,960 However, if the action is not specified, 284 00:10:45,960 --> 00:10:48,360 the entire line is going to be printed. 285 00:10:48,360 --> 00:10:51,390 The awk command can be executed from the command line 286 00:10:51,390 --> 00:10:54,750 or from within an awk script file. 287 00:10:54,750 --> 00:10:57,420 The awk command can be used to process text 288 00:10:57,420 --> 00:10:59,250 in a variety of different ways, 289 00:10:59,250 --> 00:11:02,310 including extracting text that matches a certain pattern, 290 00:11:02,310 --> 00:11:04,770 deleting text that matches a certain pattern, 291 00:11:04,770 --> 00:11:06,810 adding text that matches a certain pattern, 292 00:11:06,810 --> 00:11:08,100 and much more. 293 00:11:08,100 --> 00:11:09,600 To run awk, 294 00:11:09,600 --> 00:11:14,600 simply type in awk, options, patterns, actions, 295 00:11:14,640 --> 00:11:16,260 and file names. 296 00:11:16,260 --> 00:11:17,970 In awk scripts, 297 00:11:17,970 --> 00:11:21,240 you can also provide patterns along with blocks of code. 298 00:11:21,240 --> 00:11:23,790 If pattern matching any line in the input file, 299 00:11:23,790 --> 00:11:26,880 the code blocks in the script can then be executed. 300 00:11:26,880 --> 00:11:29,550 The pattern can include regular_expressions as well 301 00:11:29,550 --> 00:11:31,920 that will retrieve all the records that match it. 302 00:11:31,920 --> 00:11:36,920 For example, if I use / bracket abc bracket /, 303 00:11:37,020 --> 00:11:41,130 it's going to find any record that begins with a, b, or c. 304 00:11:41,130 --> 00:11:43,620 If you use the pattern relational_expressions, 305 00:11:43,620 --> 00:11:45,270 this will retrieve all the records 306 00:11:45,270 --> 00:11:47,320 whose first field contains the value abc. 307 00:11:48,270 --> 00:11:51,777 For example, $1 == "abc". 308 00:11:52,800 --> 00:11:54,500 The pattern pattern_1 && pattern_2 309 00:11:56,300 --> 00:11:58,110 is going to retrieve all the records 310 00:11:58,110 --> 00:12:00,810 whose first field contains the value abc 311 00:12:00,810 --> 00:12:03,780 and the second field contains the value 01. 312 00:12:03,780 --> 00:12:04,830 So for example, 313 00:12:04,830 --> 00:12:09,830 if I have $1 == "abc" && $2 == "01", 314 00:12:13,080 --> 00:12:15,030 this creates that pattern. 315 00:12:15,030 --> 00:12:17,100 If I want to create an OR condition, 316 00:12:17,100 --> 00:12:19,980 I can do that by using two pipe characters. 317 00:12:19,980 --> 00:12:23,617 So if I use the pattern of pattern_1 || pattern_2, 318 00:12:25,290 --> 00:12:26,970 this will retrieve all the records 319 00:12:26,970 --> 00:12:29,340 that satisfy the conditions for the first field 320 00:12:29,340 --> 00:12:33,030 that contains the values of pattern 1 or abc, 321 00:12:33,030 --> 00:12:36,990 or the second field that contains the value of 01, 322 00:12:36,990 --> 00:12:38,640 which was my second pattern, 323 00:12:38,640 --> 00:12:40,680 or even both of them. 324 00:12:40,680 --> 00:12:41,820 So for example, 325 00:12:41,820 --> 00:12:43,627 I might have somebody that looks like 326 00:12:43,627 --> 00:12:48,627 $1 == "abc" || $2 == "01", 327 00:12:50,760 --> 00:12:53,820 and this would fulfill this OR condition. 328 00:12:53,820 --> 00:12:55,560 Now, another pattern we can use 329 00:12:55,560 --> 00:12:57,390 is basically an if-then, 330 00:12:57,390 --> 00:12:58,470 and we do this by having 331 00:12:58,470 --> 00:12:59,903 pattern_1 ? pattern_2 : pattern_3. 332 00:13:03,570 --> 00:13:04,410 So what's going to happen 333 00:13:04,410 --> 00:13:06,720 is it's first going to evaluate pattern 1, 334 00:13:06,720 --> 00:13:08,250 and if it matches pattern 1, 335 00:13:08,250 --> 00:13:09,870 it's going to go to pattern 2, 336 00:13:09,870 --> 00:13:11,460 and if it matches pattern two, 337 00:13:11,460 --> 00:13:13,320 it's going to print it to the screen. 338 00:13:13,320 --> 00:13:16,740 But if it evaluates pattern 1 and it doesn't match, 339 00:13:16,740 --> 00:13:18,660 it's going to then evaluate pattern 3, 340 00:13:18,660 --> 00:13:20,220 and if it matches pattern 3, 341 00:13:20,220 --> 00:13:22,080 it'll display that to the screen. 342 00:13:22,080 --> 00:13:23,640 So what does this look like? 343 00:13:23,640 --> 00:13:24,960 Well, let's say I have something 344 00:13:24,960 --> 00:13:29,960 like $1 == "10" ? $5 == "20" : $9 == "30". 345 00:13:35,460 --> 00:13:38,820 This means that if field 1 equals 10, 346 00:13:38,820 --> 00:13:42,210 I'm going to evaluate field 5 and see if it equals 20. 347 00:13:42,210 --> 00:13:44,880 If it does, I'll print that line to the screen. 348 00:13:44,880 --> 00:13:48,870 But if I evaluated field 1 and it didn't equal 10, 349 00:13:48,870 --> 00:13:50,910 I'm then going to evaluate field 9 350 00:13:50,910 --> 00:13:52,500 and see if it equals 30, 351 00:13:52,500 --> 00:13:54,810 and if it does, I'll print it to the screen. 352 00:13:54,810 --> 00:13:57,390 In the case that any of those are not going to happen, 353 00:13:57,390 --> 00:13:59,280 we are then going to print nothing to the screen 354 00:13:59,280 --> 00:14:01,410 and evaluate the next line. 355 00:14:01,410 --> 00:14:03,120 The last pattern we need to cover 356 00:14:03,120 --> 00:14:06,030 is known as pattern_1, pattern 2, 357 00:14:06,030 --> 00:14:07,920 and this will print a range of records 358 00:14:07,920 --> 00:14:10,050 starting from the record whose first field 359 00:14:10,050 --> 00:14:12,540 contains the value of pattern 1 360 00:14:12,540 --> 00:14:16,200 and going until it finds the field of pattern 2. 361 00:14:16,200 --> 00:14:17,190 So for example, 362 00:14:17,190 --> 00:14:22,190 if I have $1 == "01", $1 == "02", 363 00:14:24,060 --> 00:14:26,490 this tells me I'm going to check the first field 364 00:14:26,490 --> 00:14:28,380 for any values of 01 365 00:14:28,380 --> 00:14:31,920 until I find ones that have 02. 366 00:14:31,920 --> 00:14:33,390 The next thing I want to talk about 367 00:14:33,390 --> 00:14:37,230 is known as a stream editor or sed command. 368 00:14:37,230 --> 00:14:40,050 The sed command is a program that you can use 369 00:14:40,050 --> 00:14:43,980 to modify text files according to various parameters. 370 00:14:43,980 --> 00:14:46,140 The sed command can also be used 371 00:14:46,140 --> 00:14:48,540 for global search and replace actions. 372 00:14:48,540 --> 00:14:51,480 Some common options here are going to be option d, 373 00:14:51,480 --> 00:14:52,890 which is used to delete lines 374 00:14:52,890 --> 00:14:55,770 that match a specific pattern or line number, 375 00:14:55,770 --> 00:14:59,820 option -n,p will be used to print only the lines 376 00:14:59,820 --> 00:15:01,530 that contain the pattern, 377 00:15:01,530 --> 00:15:03,990 option s is going to be used to substitute 378 00:15:03,990 --> 00:15:06,180 the first occurrence of the string in the file, 379 00:15:06,180 --> 00:15:08,700 and the option s,g is going to be used 380 00:15:08,700 --> 00:15:11,190 to globally substitute the original string 381 00:15:11,190 --> 00:15:12,570 with the replacement string 382 00:15:12,570 --> 00:15:14,520 for each occurrence in the file. 383 00:15:14,520 --> 00:15:16,290 The proper way to use this command 384 00:15:16,290 --> 00:15:19,680 is to type sed, the option, address, or action, 385 00:15:19,680 --> 00:15:21,660 and then the file names. 386 00:15:21,660 --> 00:15:25,050 Another command we need to talk about is the link command. 387 00:15:25,050 --> 00:15:27,060 This is known as ln. 388 00:15:27,060 --> 00:15:30,630 The ln command is used to create a link to a file. 389 00:15:30,630 --> 00:15:34,200 Linking enables a file in one directory, the link, 390 00:15:34,200 --> 00:15:37,470 to point to a file in another directory, the target. 391 00:15:37,470 --> 00:15:40,020 A link does not contain data on its own, 392 00:15:40,020 --> 00:15:42,540 only a reference to the target file. 393 00:15:42,540 --> 00:15:43,980 Any changes to the link 394 00:15:43,980 --> 00:15:46,770 will reflect into that target file as well. 395 00:15:46,770 --> 00:15:48,690 If you don't specify the link name, 396 00:15:48,690 --> 00:15:50,550 the ln command will create the link 397 00:15:50,550 --> 00:15:52,710 in your current working directory. 398 00:15:52,710 --> 00:15:54,210 The syntax of this command 399 00:15:54,210 --> 00:15:58,530 is ln, the options, the target name, and the link name. 400 00:15:58,530 --> 00:16:00,630 The ln command has various different options 401 00:16:00,630 --> 00:16:03,810 that you can use as well including -backup, 402 00:16:03,810 --> 00:16:07,151 which is used to back up existing destination files, 403 00:16:07,151 --> 00:16:09,300 F, which will be used to remove 404 00:16:09,300 --> 00:16:11,330 existing destination files, 405 00:16:11,330 --> 00:16:15,360 s, to make a symbolic link instead of a hard link, 406 00:16:15,360 --> 00:16:18,900 and -i, to prompt to remove destination files, 407 00:16:18,900 --> 00:16:23,400 and finally, -v, to print the name of a file before linking. 408 00:16:23,400 --> 00:16:24,870 Using the ln command, 409 00:16:24,870 --> 00:16:27,060 you can create two different types of links: 410 00:16:27,060 --> 00:16:30,000 these are called hard links and symbolic links. 411 00:16:30,000 --> 00:16:32,760 Now a hard link is a reference to another file 412 00:16:32,760 --> 00:16:35,640 and it enables the files data to have more than one name 413 00:16:35,640 --> 00:16:38,700 in different locations in the same file system. 414 00:16:38,700 --> 00:16:40,380 If the original file is deleted 415 00:16:40,380 --> 00:16:42,240 after the hard link is created, 416 00:16:42,240 --> 00:16:44,400 all of its contents will still be available 417 00:16:44,400 --> 00:16:45,960 in the linked file. 418 00:16:45,960 --> 00:16:48,360 A symbolic link also called a soft link 419 00:16:48,360 --> 00:16:50,250 is a reference to a file or directory 420 00:16:50,250 --> 00:16:52,890 that can span multiple different file systems. 421 00:16:52,890 --> 00:16:54,990 But if the original file or directory 422 00:16:54,990 --> 00:16:57,570 is deleted after the symbolic link is created, 423 00:16:57,570 --> 00:17:00,060 the original content is lost. 424 00:17:00,060 --> 00:17:01,770 In order to create a hard link, 425 00:17:01,770 --> 00:17:04,410 you would simply type in ln, the file you want to do, 426 00:17:04,410 --> 00:17:05,400 and then the link itself 427 00:17:05,400 --> 00:17:07,829 because the ln command uses hard links by default 428 00:17:07,829 --> 00:17:09,093 when creating a new link.