1 00:00:00,060 --> 00:00:01,020 In this lesson, 2 00:00:01,020 --> 00:00:03,180 we're going to discuss the Bash shell environment 3 00:00:03,180 --> 00:00:05,730 and how you can customize it to enhance your productivity 4 00:00:05,730 --> 00:00:07,740 when working in the command line. 5 00:00:07,740 --> 00:00:10,350 Most of us know how to use a mouse and click icons 6 00:00:10,350 --> 00:00:14,130 to access our files, programs, and folders on our devices, 7 00:00:14,130 --> 00:00:15,960 but this is just one way for us 8 00:00:15,960 --> 00:00:17,910 to communicate with our computers. 9 00:00:17,910 --> 00:00:19,320 The command line and the shell 10 00:00:19,320 --> 00:00:22,260 make up a quick, powerful text-based interface 11 00:00:22,260 --> 00:00:25,590 that developers often use more effectively and efficiently 12 00:00:25,590 --> 00:00:27,330 to communicate with their computers 13 00:00:27,330 --> 00:00:29,280 to accomplish a wide set of task 14 00:00:29,280 --> 00:00:31,920 that every system administrator is going to have to handle 15 00:00:31,920 --> 00:00:34,320 at some point in their Linux career. 16 00:00:34,320 --> 00:00:36,450 Now, scripts can greatly improve efficiency 17 00:00:36,450 --> 00:00:38,970 by minimizing the amount of repetitive typing 18 00:00:38,970 --> 00:00:41,610 that you're going to need to do at the command line interface, 19 00:00:41,610 --> 00:00:43,590 and this can enable you to get more work done 20 00:00:43,590 --> 00:00:45,480 in a shorter amount of time. 21 00:00:45,480 --> 00:00:48,000 Surprisingly, Bash is so much easier 22 00:00:48,000 --> 00:00:49,740 than any other programming language 23 00:00:49,740 --> 00:00:51,450 you might have to work with. 24 00:00:51,450 --> 00:00:53,970 You're going to learn that we can harness the power of scripts 25 00:00:53,970 --> 00:00:56,820 to really help you become more productive at doing your job 26 00:00:56,820 --> 00:00:59,910 and be able to get things done much more efficiently. 27 00:00:59,910 --> 00:01:02,910 First off, you may want to change the way things look and act 28 00:01:02,910 --> 00:01:04,410 inside of your system. 29 00:01:04,410 --> 00:01:05,910 You can make all sorts of changes 30 00:01:05,910 --> 00:01:08,010 to make things easier for you to use. 31 00:01:08,010 --> 00:01:10,110 Many people are going to change their prompts, 32 00:01:10,110 --> 00:01:11,940 the color that things are displayed in, 33 00:01:11,940 --> 00:01:14,250 the paths to make launching things easier, 34 00:01:14,250 --> 00:01:16,380 alias is to make commands easier to run, 35 00:01:16,380 --> 00:01:19,380 changing out their default editors, and much more. 36 00:01:19,380 --> 00:01:21,390 The shell environment is really the mechanism 37 00:01:21,390 --> 00:01:23,640 by which Bash or any other shell 38 00:01:23,640 --> 00:01:26,310 will maintain settings and other behavioral details 39 00:01:26,310 --> 00:01:28,170 about their own shell. 40 00:01:28,170 --> 00:01:29,730 This shell creates an environment 41 00:01:29,730 --> 00:01:31,290 when starting up a session, 42 00:01:31,290 --> 00:01:32,940 and it uses the environment settings 43 00:01:32,940 --> 00:01:35,460 to determine how to interact with the user. 44 00:01:35,460 --> 00:01:37,200 The process of creating a new session 45 00:01:37,200 --> 00:01:39,180 is called shell spawning. 46 00:01:39,180 --> 00:01:41,400 This new session is really a copy 47 00:01:41,400 --> 00:01:43,650 and it's called a child process. 48 00:01:43,650 --> 00:01:46,350 For example, the shell spawns a child process 49 00:01:46,350 --> 00:01:48,300 when the user enters a command. 50 00:01:48,300 --> 00:01:51,000 This child process becomes the new process 51 00:01:51,000 --> 00:01:53,160 and can also create other sub-processes 52 00:01:53,160 --> 00:01:55,380 or child processes from itself. 53 00:01:55,380 --> 00:01:58,140 This can result in multiple generations of processes 54 00:01:58,140 --> 00:02:00,420 in a nested tree architecture. 55 00:02:00,420 --> 00:02:03,510 Now, each process is going to call upon the shell environment 56 00:02:03,510 --> 00:02:06,810 and pass its details onto the next generation going upward 57 00:02:06,810 --> 00:02:09,479 until it reaches the kernel and the processor. 58 00:02:09,479 --> 00:02:11,009 Now, when I talk about a script, 59 00:02:11,009 --> 00:02:13,350 I'm really talking about any computer program 60 00:02:13,350 --> 00:02:15,390 that automates the execution of tasks 61 00:02:15,390 --> 00:02:18,180 for particular runtime or shell environment. 62 00:02:18,180 --> 00:02:20,670 Scripts are written in scripting languages, 63 00:02:20,670 --> 00:02:23,640 which are really just a subset of programming languages. 64 00:02:23,640 --> 00:02:26,580 Scripts typically are not full-fledged programs, 65 00:02:26,580 --> 00:02:29,340 but instead they have a much more limited feature set. 66 00:02:29,340 --> 00:02:31,500 And this is used to integrate with other programs 67 00:02:31,500 --> 00:02:33,030 and operating system components 68 00:02:33,030 --> 00:02:36,420 to achieve the automation and efficiency you're looking for. 69 00:02:36,420 --> 00:02:37,950 Think about a script in programming 70 00:02:37,950 --> 00:02:41,430 the way we use scripts in plays or movies or TV shows. 71 00:02:41,430 --> 00:02:43,680 The script is telling the actors what they should say 72 00:02:43,680 --> 00:02:45,120 and what they should do. 73 00:02:45,120 --> 00:02:46,650 Well, in our world, 74 00:02:46,650 --> 00:02:49,500 a script is going to tell the shell exactly what it should do 75 00:02:49,500 --> 00:02:51,600 to accomplish a given task. 76 00:02:51,600 --> 00:02:52,650 Now, as I said, 77 00:02:52,650 --> 00:02:54,810 you can change the details of your environment 78 00:02:54,810 --> 00:02:55,890 within the shell, 79 00:02:55,890 --> 00:02:59,400 and you do this by changing its variables and their values. 80 00:02:59,400 --> 00:03:02,010 Variables refer to things where the values can change 81 00:03:02,010 --> 00:03:03,360 from time to time. 82 00:03:03,360 --> 00:03:05,760 Think about it as a big placeholder. 83 00:03:05,760 --> 00:03:07,200 Most variables are going to be set 84 00:03:07,200 --> 00:03:09,450 either by the operating system when you log in 85 00:03:09,450 --> 00:03:12,930 or by the shell when you invoke it initially. 86 00:03:12,930 --> 00:03:14,760 These variables are the key components 87 00:03:14,760 --> 00:03:16,410 that comprise the shell environment 88 00:03:16,410 --> 00:03:18,180 and tell the shell how it should operate 89 00:03:18,180 --> 00:03:20,880 and how it should act and present itself to you. 90 00:03:20,880 --> 00:03:23,430 For example, you can set shell variables 91 00:03:23,430 --> 00:03:26,430 by typing VAR equals and the value. 92 00:03:26,430 --> 00:03:29,730 So if I wanted to create a variable called MYVARIABLE, 93 00:03:29,730 --> 00:03:33,120 I can say MYVARIABLE=123, 94 00:03:33,120 --> 00:03:36,120 and this will be able to have that new word, MYVARIABLE, 95 00:03:36,120 --> 00:03:38,520 reference the number 123. 96 00:03:38,520 --> 00:03:41,520 Anytime I want to pull out the information from that variable, 97 00:03:41,520 --> 00:03:43,260 I'll simply type it out in the format 98 00:03:43,260 --> 00:03:46,620 of dollar sign, curly bracket, the variable name, 99 00:03:46,620 --> 00:03:47,970 and curly bracket. 100 00:03:47,970 --> 00:03:49,620 And this can be used inside of your scripts 101 00:03:49,620 --> 00:03:51,240 to retrieve the value from the variable 102 00:03:51,240 --> 00:03:54,330 and then perform logical functions or commands upon it. 103 00:03:54,330 --> 00:03:56,670 For example, if I wanted to display the contents 104 00:03:56,670 --> 00:03:58,380 of my variable to the screen, 105 00:03:58,380 --> 00:04:01,293 I would simply enter echo ${MYVARIABLE} 106 00:04:04,350 --> 00:04:05,760 at the command line environment 107 00:04:05,760 --> 00:04:06,930 and hit Enter. 108 00:04:06,930 --> 00:04:09,000 Then I'm going to see what is echoed, 109 00:04:09,000 --> 00:04:13,050 which is the contents of that variable, which was 123. 110 00:04:13,050 --> 00:04:15,720 Now, there are some built in environmental variables 111 00:04:15,720 --> 00:04:19,140 that you're going to come across as well inside of Bash. 112 00:04:19,140 --> 00:04:23,190 This includes things like path and shell and HISTSIZE. 113 00:04:23,190 --> 00:04:24,023 Let's talk a little bit about 114 00:04:24,023 --> 00:04:26,100 these different environmental variables. 115 00:04:26,100 --> 00:04:27,540 Now, an environmental variable 116 00:04:27,540 --> 00:04:29,220 is really a variable that's inherited 117 00:04:29,220 --> 00:04:30,960 from the parent shell process, 118 00:04:30,960 --> 00:04:32,520 and it's subsequently going to be passed on 119 00:04:32,520 --> 00:04:35,070 to any child processes that respond. 120 00:04:35,070 --> 00:04:37,800 These environmental variables can consist of a name, 121 00:04:37,800 --> 00:04:40,830 usually written in upper case letters, and then a value. 122 00:04:40,830 --> 00:04:43,260 For example, if I'm using the path variable, 123 00:04:43,260 --> 00:04:45,720 it's going to contain the name of the path. 124 00:04:45,720 --> 00:04:47,670 Some of the default environmental variables 125 00:04:47,670 --> 00:04:49,260 include certain functions, 126 00:04:49,260 --> 00:04:50,370 such as HOSTNAME, 127 00:04:50,370 --> 00:04:53,010 which is going to be set to the host name of the system. 128 00:04:53,010 --> 00:04:55,710 SHELL, which is going to be set to the shell path 129 00:04:55,710 --> 00:04:59,250 for the system such as /bin/bash. 130 00:04:59,250 --> 00:05:01,710 MAIL, which is going to be set to where the mail 131 00:05:01,710 --> 00:05:03,480 is going to be stored on a given system, 132 00:05:03,480 --> 00:05:04,313 HOME. 133 00:05:04,313 --> 00:05:06,240 This is a variable that defines the home directory 134 00:05:06,240 --> 00:05:07,350 for the user. 135 00:05:07,350 --> 00:05:08,220 PATH. 136 00:05:08,220 --> 00:05:10,050 This is a variable where it's going to specify 137 00:05:10,050 --> 00:05:11,790 the search path that you should look for 138 00:05:11,790 --> 00:05:13,350 whenever you invoke a command 139 00:05:13,350 --> 00:05:14,820 because it knows those are places 140 00:05:14,820 --> 00:05:18,900 that commands are usually kept, such as the /bin directory. 141 00:05:18,900 --> 00:05:19,980 HISTSIZE. 142 00:05:19,980 --> 00:05:22,320 This is a variable that specifies the number of entries 143 00:05:22,320 --> 00:05:24,150 that are stored in the command history 144 00:05:24,150 --> 00:05:25,800 inside that given shell. 145 00:05:25,800 --> 00:05:26,850 And USER. 146 00:05:26,850 --> 00:05:28,620 This is a variable that specifies the name 147 00:05:28,620 --> 00:05:31,080 of the user that's currently logged in. 148 00:05:31,080 --> 00:05:33,060 Now, environmental variables can also be used 149 00:05:33,060 --> 00:05:35,040 to configure localization options 150 00:05:35,040 --> 00:05:40,040 by editing things inside the /etc/locale.conf file 151 00:05:40,530 --> 00:05:44,040 and then assign the appropriate locale to the variable. 152 00:05:44,040 --> 00:05:47,100 The LC_*variable is going to specify 153 00:05:47,100 --> 00:05:50,070 a collection of localization environmental variables. 154 00:05:50,070 --> 00:05:53,100 The LANG variable is going to specify the locale to use 155 00:05:53,100 --> 00:05:57,900 for all the LC_* variables that aren't explicitly defined. 156 00:05:57,900 --> 00:06:00,210 The LC_ALL is going to be a variable 157 00:06:00,210 --> 00:06:02,880 that specifies the locality use for all options. 158 00:06:02,880 --> 00:06:04,380 And this will override whatever is stored 159 00:06:04,380 --> 00:06:07,350 in LANG and LC_*. 160 00:06:07,350 --> 00:06:09,990 Another environmental variable you can use for localization 161 00:06:09,990 --> 00:06:13,350 is for time zone, which is written as TZ. 162 00:06:13,350 --> 00:06:14,730 TZ stands for time zone, 163 00:06:14,730 --> 00:06:17,520 and it specifies the time zone of your given system 164 00:06:17,520 --> 00:06:19,890 and stores that in that variable. 165 00:06:19,890 --> 00:06:22,290 Now, you can effectively change a shell variable 166 00:06:22,290 --> 00:06:23,970 into an environmental variable 167 00:06:23,970 --> 00:06:26,400 by simply using the export command. 168 00:06:26,400 --> 00:06:29,790 For example, if you have a shell variable called SHELL_VAR, 169 00:06:29,790 --> 00:06:31,770 you can enter export SHELL_VAR 170 00:06:31,770 --> 00:06:34,050 to make it an environmental variable. 171 00:06:34,050 --> 00:06:35,820 You can also change the value of the variable 172 00:06:35,820 --> 00:06:37,170 while you're exporting it 173 00:06:37,170 --> 00:06:39,630 by including the existing environmental variables 174 00:06:39,630 --> 00:06:41,280 and the equal sign. 175 00:06:41,280 --> 00:06:43,260 To do this you can enter something like, 176 00:06:43,260 --> 00:06:48,260 export SHELL_VAR="New value" at your command line. 177 00:06:48,720 --> 00:06:50,160 To run the export command, 178 00:06:50,160 --> 00:06:53,670 simply type in export, the options, and the variable name, 179 00:06:53,670 --> 00:06:56,610 and then the value if you're going to use that option. 180 00:06:56,610 --> 00:06:57,600 The next command we have 181 00:06:57,600 --> 00:07:01,410 is known as the environment command, spelled env. 182 00:07:01,410 --> 00:07:03,750 The env Command is used to run a command 183 00:07:03,750 --> 00:07:06,300 with modified environmental variables. 184 00:07:06,300 --> 00:07:08,070 To do this, you're going to simply supply 185 00:07:08,070 --> 00:07:09,270 the name of a variable 186 00:07:09,270 --> 00:07:11,730 and a value in key value pair format 187 00:07:11,730 --> 00:07:13,680 as well as the command that you want to run. 188 00:07:13,680 --> 00:07:14,670 And this will be able to change 189 00:07:14,670 --> 00:07:16,380 the value of the specified variable 190 00:07:16,380 --> 00:07:19,020 for that particular command session only. 191 00:07:19,020 --> 00:07:22,800 To run this, simply type in env, the options, 192 00:07:22,800 --> 00:07:25,140 the name of the variable equals the value, 193 00:07:25,140 --> 00:07:27,090 and the command you want to run. 194 00:07:27,090 --> 00:07:29,190 If you want to see all of the shell variables, 195 00:07:29,190 --> 00:07:31,560 environmental variables, and shell functions, 196 00:07:31,560 --> 00:07:33,990 you can do this by using this set command. 197 00:07:33,990 --> 00:07:37,080 Simply type in set and hit Enter without any arguments 198 00:07:37,080 --> 00:07:38,850 to print out all of your shell variables, 199 00:07:38,850 --> 00:07:41,460 environmental variables, and shell functions. 200 00:07:41,460 --> 00:07:42,900 You can also use the set command 201 00:07:42,900 --> 00:07:44,880 to enable the use of options in a shell script 202 00:07:44,880 --> 00:07:46,740 to change its behavior too. 203 00:07:46,740 --> 00:07:48,510 Now, to summarize some of the differences 204 00:07:48,510 --> 00:07:49,830 between these three commands, 205 00:07:49,830 --> 00:07:51,240 let's do a quick review. 206 00:07:51,240 --> 00:07:53,850 The export command is going to change the value of the variable 207 00:07:53,850 --> 00:07:55,890 for all of your child processes, 208 00:07:55,890 --> 00:07:57,000 the environmental command 209 00:07:57,000 --> 00:07:58,770 is going to view the environmental variables 210 00:07:58,770 --> 00:08:00,720 or change the value of a variable 211 00:08:00,720 --> 00:08:02,820 for a specified command being run, 212 00:08:02,820 --> 00:08:05,460 and the set command is going to view all the shell variables 213 00:08:05,460 --> 00:08:06,960 or environmental variables 214 00:08:06,960 --> 00:08:10,380 and it can be used to change the value of shell attributes. 215 00:08:10,380 --> 00:08:13,320 All right, the next thing we're going to talk about is search, 216 00:08:13,320 --> 00:08:14,190 and I mentioned earlier 217 00:08:14,190 --> 00:08:16,950 that we had an environmental variable called path. 218 00:08:16,950 --> 00:08:19,050 Well, a search path is really a sequence 219 00:08:19,050 --> 00:08:20,610 of various directory paths 220 00:08:20,610 --> 00:08:23,340 that's going to be used by the shell to locate files. 221 00:08:23,340 --> 00:08:24,870 These paths can be assigned 222 00:08:24,870 --> 00:08:26,820 to the path environmental variable, 223 00:08:26,820 --> 00:08:30,030 and the path variable has a list of all the directory names 224 00:08:30,030 --> 00:08:31,890 separated by colons. 225 00:08:31,890 --> 00:08:33,450 You can also set a new path 226 00:08:33,450 --> 00:08:36,510 to the existing group of path names, modify that path, 227 00:08:36,510 --> 00:08:38,730 or delete a path by overwriting the contents 228 00:08:38,730 --> 00:08:40,470 of this variable. 229 00:08:40,470 --> 00:08:41,700 Now, earlier I talked about 230 00:08:41,700 --> 00:08:44,010 the HISTSIZE environmental variable. 231 00:08:44,010 --> 00:08:45,570 There's also a companion one to this 232 00:08:45,570 --> 00:08:48,030 known as the HISTFILESIZE variable. 233 00:08:48,030 --> 00:08:49,260 This is a shell variable 234 00:08:49,260 --> 00:08:51,660 that enables you to set the maximum number of lines 235 00:08:51,660 --> 00:08:54,090 contained in the command history file. 236 00:08:54,090 --> 00:08:55,980 This is slightly different than HISTSIZE, 237 00:08:55,980 --> 00:08:58,740 because HISTSIZE is telling you how many commands 238 00:08:58,740 --> 00:09:00,090 you can store in memory, 239 00:09:00,090 --> 00:09:03,150 but HISTFILESIZE tells you how many you can store 240 00:09:03,150 --> 00:09:05,250 in the command's history file. 241 00:09:05,250 --> 00:09:07,920 By overriding the value of the HISTFILESIZE, 242 00:09:07,920 --> 00:09:11,220 you can set exactly how many lines or previous commands 243 00:09:11,220 --> 00:09:14,070 you want to be able to have stored in that file. 244 00:09:14,070 --> 00:09:17,370 For example, if you assign a value of 20 to this variable, 245 00:09:17,370 --> 00:09:21,120 the history file will cut off after it gets 20 lines. 246 00:09:21,120 --> 00:09:24,270 By default, the value of this variable is 1000, 247 00:09:24,270 --> 00:09:26,070 meaning your system is memorizing 248 00:09:26,070 --> 00:09:29,370 the last 1000 things you've done in the command line 249 00:09:29,370 --> 00:09:31,890 and storing that in the history file. 250 00:09:31,890 --> 00:09:34,410 Another command we have is known as alias. 251 00:09:34,410 --> 00:09:37,320 The alias command is used to customize the shell environment 252 00:09:37,320 --> 00:09:39,630 by generating command line aliases. 253 00:09:39,630 --> 00:09:41,940 Now, aliases are essentially short hands 254 00:09:41,940 --> 00:09:43,410 for longer expressions. 255 00:09:43,410 --> 00:09:46,590 And by using aliases, you can create short sequences 256 00:09:46,590 --> 00:09:49,290 that you can type in to represent longer commands 257 00:09:49,290 --> 00:09:52,200 and all the various options and arguments it has. 258 00:09:52,200 --> 00:09:54,600 For example, I often find myself using 259 00:09:54,600 --> 00:09:57,900 the ls -la command. 260 00:09:57,900 --> 00:10:00,210 This tells me to list out things in a directory 261 00:10:00,210 --> 00:10:01,980 and showing me everything there 262 00:10:01,980 --> 00:10:03,390 in a list that I can understand 263 00:10:03,390 --> 00:10:05,490 and see all of their different characteristics, 264 00:10:05,490 --> 00:10:07,980 such as the owners and the file permissions. 265 00:10:07,980 --> 00:10:10,260 But if I didn't want to type that out each time, 266 00:10:10,260 --> 00:10:13,050 I can create an alias called myls 267 00:10:13,050 --> 00:10:16,980 that then includes the ls -la command inside of it. 268 00:10:16,980 --> 00:10:20,670 To do this, we can go ahead and set it by typing an alias, 269 00:10:20,670 --> 00:10:23,760 the alias name, equals, and the command with options. 270 00:10:23,760 --> 00:10:27,937 So in my case, that would be alias, myls='la -ls' 271 00:10:31,320 --> 00:10:33,120 Now, after running this alias command, 272 00:10:33,120 --> 00:10:36,360 anytime I type in myls in the command line, 273 00:10:36,360 --> 00:10:38,160 it's going to execute the substitute command 274 00:10:38,160 --> 00:10:39,600 that I made the alias for, 275 00:10:39,600 --> 00:10:41,820 which was ls -la. 276 00:10:41,820 --> 00:10:44,130 This is really helpful when you have very long commands 277 00:10:44,130 --> 00:10:44,963 you want to run 278 00:10:44,963 --> 00:10:46,530 and you want to use this as a shorthand. 279 00:10:46,530 --> 00:10:48,660 In this case, I didn't save that much effort 280 00:10:48,660 --> 00:10:50,790 because myls is four characters 281 00:10:50,790 --> 00:10:53,910 and ls -la is six characters. 282 00:10:53,910 --> 00:10:56,250 So it didn't save me too much time here. 283 00:10:56,250 --> 00:10:57,720 Now, another thing you want to think about 284 00:10:57,720 --> 00:10:59,670 is how you can find out how long it takes 285 00:10:59,670 --> 00:11:00,990 for a command to run, 286 00:11:00,990 --> 00:11:02,460 and this will be able to give you a better idea 287 00:11:02,460 --> 00:11:05,370 how you can optimize your frequently used tasks. 288 00:11:05,370 --> 00:11:08,010 To do this, you can use the time command. 289 00:11:08,010 --> 00:11:09,900 The time command is used to gather information 290 00:11:09,900 --> 00:11:12,720 about how long it takes to execute a given command 291 00:11:12,720 --> 00:11:15,750 as well some additional statistics about the input output 292 00:11:15,750 --> 00:11:18,690 and memory used by that command's execution. 293 00:11:18,690 --> 00:11:20,910 By default, the time command is going to give you 294 00:11:20,910 --> 00:11:23,700 three different pieces of statistical information. 295 00:11:23,700 --> 00:11:25,560 The first is the real time that elapsed 296 00:11:25,560 --> 00:11:27,390 between when you started running the command 297 00:11:27,390 --> 00:11:29,040 and when it terminated, 298 00:11:29,040 --> 00:11:31,050 the second is the amount of time spent 299 00:11:31,050 --> 00:11:33,060 running the code inside the user space, 300 00:11:33,060 --> 00:11:35,580 which is known as the user CPU time, 301 00:11:35,580 --> 00:11:38,100 and the third is the system CPU time, 302 00:11:38,100 --> 00:11:39,630 which is the time spent running the code 303 00:11:39,630 --> 00:11:41,370 inside the kernel space. 304 00:11:41,370 --> 00:11:43,410 So by having these three pieces of information 305 00:11:43,410 --> 00:11:45,060 you have the total amount of time, 306 00:11:45,060 --> 00:11:47,880 the time in user space, and the time in kernel space. 307 00:11:47,880 --> 00:11:49,920 This can tell you a lot about a given program 308 00:11:49,920 --> 00:11:51,180 and what permissions it's using 309 00:11:51,180 --> 00:11:53,550 at certain times during it's execution. 310 00:11:53,550 --> 00:11:54,690 To run the time command, 311 00:11:54,690 --> 00:11:56,790 simply type in time, the options, 312 00:11:56,790 --> 00:11:59,190 and the command that you want to evaluate. 313 00:11:59,190 --> 00:12:01,290 All right, we covered a lot in this lesson, 314 00:12:01,290 --> 00:12:02,940 but let's do a quick recap 315 00:12:02,940 --> 00:12:05,190 of what you can do when things go wrong. 316 00:12:05,190 --> 00:12:07,080 Sometimes you're going to encounter some issues 317 00:12:07,080 --> 00:12:07,913 when you're using 318 00:12:07,913 --> 00:12:10,800 or customizing these Bash shell environmental variables. 319 00:12:10,800 --> 00:12:13,110 When you add an alias, if you get an error, 320 00:12:13,110 --> 00:12:14,760 always go back and check your syntax 321 00:12:14,760 --> 00:12:16,620 to make sure you typed it in correctly. 322 00:12:16,620 --> 00:12:19,020 Whenever you're executing scripts or other programs, 323 00:12:19,020 --> 00:12:20,850 if they're not stored in a normal location 324 00:12:20,850 --> 00:12:22,080 for executable files, 325 00:12:22,080 --> 00:12:23,790 they may have trouble finding them. 326 00:12:23,790 --> 00:12:25,740 And so you may need to add their location 327 00:12:25,740 --> 00:12:26,970 to the path variable, 328 00:12:26,970 --> 00:12:29,070 or you're going to have to execute those 329 00:12:29,070 --> 00:12:32,730 by using a dot slash proceeding the command or script's name 330 00:12:32,730 --> 00:12:36,510 to say use the one right here in this current directory. 331 00:12:36,510 --> 00:12:38,340 Remember, if you need to set a variable 332 00:12:38,340 --> 00:12:40,320 for all your shell child processes, 333 00:12:40,320 --> 00:12:42,480 you're going to use the export command. 334 00:12:42,480 --> 00:12:45,240 Also, remember all your environmental variables 335 00:12:45,240 --> 00:12:48,090 do get stored by default in your Bash profile. 336 00:12:48,090 --> 00:12:50,100 So you can configure the environmental variables 337 00:12:50,100 --> 00:12:52,720 inside that file by going to -/.bash_profile 338 00:12:56,190 --> 00:12:57,930 and making those variables available 339 00:12:57,930 --> 00:13:00,210 to all of your shells by default. 340 00:13:00,210 --> 00:13:02,190 For example, if you have a service account 341 00:13:02,190 --> 00:13:04,290 that requires certain environmental variables, 342 00:13:04,290 --> 00:13:06,780 you can set those up inside your Bash profile 343 00:13:06,780 --> 00:13:07,920 for that account. 344 00:13:07,920 --> 00:13:10,200 Just edit the Bash profile file 345 00:13:10,200 --> 00:13:11,760 to change those default variables, 346 00:13:11,760 --> 00:13:12,930 and it will then inherit those 347 00:13:12,930 --> 00:13:15,000 every time you launch a new shell. 348 00:13:15,000 --> 00:13:16,710 Finally, sometimes it's important 349 00:13:16,710 --> 00:13:18,480 that you set environmental variables 350 00:13:18,480 --> 00:13:20,070 for certain software packages 351 00:13:20,070 --> 00:13:22,110 based on the dependencies they have. 352 00:13:22,110 --> 00:13:24,960 For example, let's say that we have a Java application 353 00:13:24,960 --> 00:13:27,360 that relies on the Java runtime environment. 354 00:13:27,360 --> 00:13:29,160 It may only be able to find and access 355 00:13:29,160 --> 00:13:30,240 that runtime environment 356 00:13:30,240 --> 00:13:32,790 if it's referenced inside the path variable, 357 00:13:32,790 --> 00:13:34,980 which is an environmental variable after all. 358 00:13:34,980 --> 00:13:35,940 So you always need to make sure 359 00:13:35,940 --> 00:13:38,610 these things are working properly and working together 360 00:13:38,610 --> 00:13:41,060 to allow you to use your system more effectively.