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Tutorial10: Shell Scripting - Part 1

801 bytes added, 2 March
Using Variables in Shell Scripts
''<b>User-defined variables</b> are variables which can be '''created by the user''' and exist in the session. This means that no one can access user-defined variables that have been set by another user,<br>and when the session is closed these variables expire.''<br>Reference: https://mariadb.com/kb/en/user-defined-variables/
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Data can be stored and removed within a variable using an '''equal sign'''.<br><br>The '''read''' command can be used to prompt the user to enter data into a variable.<br>Refer to the diagram on the right-side to see how user-defined variables are assigned data.
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'''Positional Parameters and Special Parameters'''
Refer to the diagram to the right for examples using positional and special parameters.
 
 
'''Command Substitution:'''
 
[[Image:for-command-substitution.png|thumb|right|300px|Example of how a '''for loop with command substitution''' works.]]
<i>'''Command substitution''' is a facility that allows a command<br>to be run and its output to be pasted back on the command line as arguments to another command.</i><br>Reference: https://en.wikipedia.org/wiki/Command_substitution<br><br>
 
''Usage:''
 
<span style="font-family:courier"><b>command1 $(command2)</b><br>or<br><b>command1 `command2`</b></span><br><br>
 
''Examples:''
 
<span style="font-family:courier;font-weight:bold">file $(ls)<br>mail -s "message" $(cat email-list.txt) < message.txt<br>echo "The current directory is $(pwd)"<br>echo "The current hostname is $(hostname)"<br>echo "The date is: $(date +'%A %B %d, %Y')"<br>
===Using Control Flow Statements in Shell Scripts===
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