CSCI 330 The UNIX System
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CSCI 330 THE UNIX SYSTEM Shell Data Handling: Redirection and Piping
description
CSCI 330 The UNIX System. Shell Data Handling: Redirection and Piping. Output. The output statement of the shell is the “echo” command Syntax: echo [option] arg1 arg2 …argN its arguments can be strings or variables option “-n” will suppress trailing newline. Output with echo. Examples: - PowerPoint PPT Presentation
Transcript of CSCI 330 The UNIX System
CSCI 330THE UNIX SYSTEM
Shell Data Handling: Redirection and Piping
OUTPUT
The output statement of the shell is the “echo” command
Syntax: echo [option] arg1 arg2 …argN its arguments can be strings or variables option “-n” will suppress trailing newline
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OUTPUT WITH ECHO
Examples:% echo “Hello Ray"Hello Ray% echo “Hello $USER"Hello a132436% echo “It is now `date`”It is now Mon Feb 25 10:24:08 CST 2008
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OUTPUT REDIRECTION (>)
Syntax: command > fileSends output of command to file, instead of to terminal
Examples:% du > status
% (date; du) > status
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Calls the disk usage command for the current directory and redirects the output to a file called ‘status’
( ) indicates command groups. Use it to combine the output of multiple commands. In this example, we place time and date in front of the disk usage
INPUT REDIRECTION (<)
Syntax: Command < fileCommand will read (take input) from file, instead of from terminal
Example:% tr “[A-Z]” “[a-z]” < report.input
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EXAMPLES: OUTPUT / INPUT
Redirecting input and output:% tr ‘[A-Z]’ ‘[a-z]’ < r.in > r.out
Output of command becomes input to next:% ls > temp.txt; wc < temp.txt
Eliminate the middleman: pipe% ls | wc
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APPENDING OUTPUT
Syntax: command >> fileadds output of command at the end of file If file does not exist, shell creates it
Examples:% date > usage-status% ls -l >> usage-status% du -s >> usage-status
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Build the file ‘usage-status’ from the output of the ‘date’, ‘ls’, and ‘du’ commands
SUMMARY: REDIRECTIONS AND PIPE
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Command Syntax Meaning
command < file Redirect input from file to command
command > file Redirect output from command to file
command >> file Redirect output of command and appends it to file
command1 | command2 Take/pipe output of command1 as input to command2
