Unix Tutorial

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CHAPTER 19 <strong>Unix</strong> – Shell Substitutions What is Substitution? The shell performs substitution when it encounters an expression that contains one or more special characters. Example: Following is the example, while printing value of the variable its substitued by its value. Same time "\n" is substituted by a new line: #!/bin/sh a=10 echo -e "Value of a is $a \n" This would produce following result. Here -e option enables interpretation of backslash escapes. Value of a is 10 Here is the result without -e option: Value of a is 10\n Here are following escape sequences which can be used in echo command: Escape Description \\ Backslash \a alert (BEL) \b Backspace \c suppress trailing newline \f form feed TUTORIALS POINT Simply Easy Learning
\n new line \r carriage return \t horizontal tab \v vertical tab You can use -E option to disable interpretation of backslash escapes (default). You can use -n option to disable insertion of new line. Command Substitution: Command substitution is the mechanism by which the shell performs a given set of commands and then substitutes their output in the place of the commands. Syntax: The command substitution is performed when a command is given as: `command` When performing command substitution make sure that you are using the backquote, not the single quote character. Example: Command substitution is generally used to assign the output of a command to a variable. Each of the following examples demonstrate command substitution: #!/bin/sh DATE=`date` echo "Date is $DATE" USERS=`who | wc -l` echo "Logged in user are $USERS" UP=`date ; uptime` echo "Uptime is $UP" This will produce following result: Date is Thu Jul 2 03:59:57 MST 2009 Logged in user are 1 Uptime is Thu Jul 2 03:59:57 MST 2009 03:59:57 up 20 days, 14:03, 1 user, load avg: 0.13, 0.07, 0.15 Variable Substitution: Variable substitution enables the shell programmer to manipulate the value of a variable based on its state. Here is the following table for all the possible substitutions: TUTORIALS POINT Simply Easy Learning
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Unix Tutorial
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ABOUT THE TUTORIAL Unix Tutorial UN
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Renaming Directories: .............
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Extended Shell Scripts: ...........
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Example: ..........................
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Trapping Signals: .................
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The main concept that unites all ve
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New UNIX password:******* Retype ne
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CHAPTER 2 Unix File Management All
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Displays all the files whose name s
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4. Fourth Column: represents file n
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CHAPTER 3 Unix Directories Adirecto
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Creates the directories docs and pu
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CHAPTER 4 Unix File Permission Setu
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$ls -l testfile -rw-rwxrwx 1 amrood
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The SUID and SGID bits will appear
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Note - The shell initialization pro
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The default secondary prompt is > (
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CHAPTER 6 Java Basic Utilities So f
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laserp-574 grace 82744 Nov 7 11:28
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CHAPTER 7 Unix Pipes and Filters Yo
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This pipe sorts all files in your d
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The process runs in the foreground,
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$kill -9 6738 Terminated Parent and
Page 49 and 50: CHAPTER 9 Unix Communication When y
Page 51 and 52: prompt on Turns prompt on. Dir List
Page 53 and 54: No Plan. Check all the logged in us
Page 55 and 56: ~ ~ ~ ~ ~ ~ ~ ~ "testfile" [New Fil
Page 57 and 58: Command CTRL+d CTRL+d CTRL+f CTRL+u
Page 59 and 60: ^G U U J Press CNTRL and G keys at
Page 61 and 62: IMPORTANT: Here are the key points
Page 63 and 64: POSIX shell ( sh) The different C-t
Page 65 and 66: CHAPTER 12 Unix- Using Variables Av
Page 67 and 68: NAME="Zara Ali" unset NAME echo $NA
Page 69 and 70: Command-Line Arguments: The command
Page 71 and 72: CHAPTER 14 Unix - Using Arrays Ashe
Page 73 and 74: CHAPTER 15 Unix - Basic Operators T
Page 75 and 76: val=`expr $b / $a` echo "b / a : $v
Page 77 and 78: else echo "$a -ge $b: a is not grea
Page 79 and 80: != Checks if the value of two opera
Page 81 and 82: ] is true. -x file Check if file is
Page 83 and 84: Right shift == String comparison fo
Page 85 and 86: -r file Checks if file is readable
Page 87 and 88: Example: #!/bin/sh a=10 b=20 if [ $
Page 89 and 90: There is only one form of case...es
Page 91 and 92: CHAPTER 17 Unix - Shell Loops Loops
Page 93 and 94: done This will produce following re
Page 95 and 96: 4) juice 5) appe 6) all 7) none #?
Page 97 and 98: CHAPTER 18 Unix - Loop Control So f
Page 99: 1 0 1 5 The continue statement: The
Page 103 and 104: CHAPTER 20 Unix - Quoting Mechanism
Page 105 and 106: The Double Quotes: Try to execute t
Page 107 and 108: CHAPTER 21 Unix - IO Redirections M
Page 109 and 110: EOF 3 $ This is a simple lookup pro
Page 111 and 112: CHAPTER 22 Unix - Shell Functions F
Page 113 and 114: echo "Return value is $ret" This wo
Page 115 and 116: CHAPTER 23 Unix - Manpage Help All
Page 117 and 118: CHAPTER 24 Unix - Regular Expressio
Page 119 and 120: Try out the following address range
Page 121 and 122: sys:x:3:3:sys:/dev:/bin/sh sync:x:4
Page 123 and 124: [0-9] Matches a single number [a-zA
Page 125 and 126: (555)555-1213 (555)555-1214 (666)55
Page 127 and 128: dev /etc /lib /boot /home /mnt /pro
Page 129 and 130: $du -h /etc 5k /etc/cron.d 63k /etc
Page 131 and 132: CHAPTER 26 Unix - User Administrati
Page 133 and 134: $ groupdel developer This removes o
Page 135 and 136: CHAPTER 27 Unix - System Performanc
Page 137 and 138: CHAPTER 28 Unix - System Logging Un
Page 139 and 140: The combination of facilities and l
Page 141 and 142: Unix - Signals and Traps CHAPTER 29
Page 143 and 144: Trapping these signals is quite eas
Page 145 and 146: CHAPTER 30 Unix - Useful Commands T
Page 147 and 148: Ispell Emacs ex, edit Emacs Emacs C
Page 149 and 150: Command Dbx Gdb Make Nm Size Strip
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Reset Reset terminal mode Script Ke
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