Unix Tutorial

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Form ${var} ${var:-word} ${var:=word} ${var:?message} ${var:+word} Description Substitue the value of var. If var is null or unset, word is substituted for var. The value of var does not change. If var is null or unset, var is set to the value of word. If var is null or unset, message is printed to standard error. This checks that variables are set correctly. If var is set, word is substituted for var. The value of var does not change. Example: Following is the example to show various states of the above substitution: #!/bin/sh echo ${var:-"Variable is not set"} echo "1 - Value of var is ${var}" echo ${var:="Variable is not set"} echo "2 - Value of var is ${var}" unset var echo ${var:+"This is default value"} echo "3 - Value of var is $var" var="Prefix" echo ${var:+"This is default value"} echo "4 - Value of var is $var" echo ${var:?"Print this message"} echo "5 - Value of var is ${var}" This would produce following result: Variable is not set 1 - Value of var is Variable is not set 2 - Value of var is Variable is not set 3 - Value of var is This is default value 4 - Value of var is Prefix Prefix 5 - Value of var is Prefix TUTORIALS POINT Simply Easy Learning
CHAPTER 20 <strong>Unix</strong> – Quoting Mechanisms The Metacharacters <strong>Unix</strong> shell provides various metacharacters which have special meaning while using them in any Shell Script and causes termination of a word unless quoted. For example ? matches with a single charater while listing files in a directory and an * would match more than one characters. Here is a list of most of the shell special characters (also called metacharacters): * ? [ ] ' " \ $ ; & ( ) | ^ < > new-line space tab A character may be quoted (i.e., made to stand for itself) by preceding it with a \. Example: Following is the example which show how to print a * or a?: #!/bin/sh echo Hello; Word This would produce following result. Hello ./test.sh: line 2: Word: command not found shell returned 127 Now let us try using a quoted character: #!/bin/sh echo Hello\; Word This would produce following result: Hello; Word 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
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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 and 100: 1 0 1 5 The continue statement: The
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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
Page 151 and 152: Reset Reset terminal mode Script Ke
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