1. CSCI 330 - The UNIX System Shell Data Handling: Redirection and Piping
NIU - Department of Computer Science

2. Output The output statement of the shell is the “echo” command
The C Shell
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
CSCI The UNIX System
Copyright Department of Computer Science, Northern Illinois University, 2005

3. Output with echo Examples: % echo “Hello Ray" Hello Ray
The C Shell
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
CSCI The UNIX System
Copyright Department of Computer Science, Northern Illinois University, 2005

4. Output Redirection (>)
The C Shell
Output Redirection (>)
Syntax: command > file
Sends output of command to file, instead of to terminal
Examples:
% du > status
% (date; du) > status
Calls the disk usage command for the current directory and redirects the output to a file called ‘status’
CSCI The UNIX System
( ) 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
Copyright Department of Computer Science, Northern Illinois University, 2005

5. Input Redirection (<)
The C Shell
Input Redirection (<)
Syntax: Command < file
Command will read (take input) from file, instead of from terminal
Example:
% tr “[A-Z]” “[a-z]” < report.input
CSCI The UNIX System
Copyright Department of Computer Science, Northern Illinois University, 2005

6. Examples: Output / Input
The C Shell
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
CSCI The UNIX System
Copyright Department of Computer Science, Northern Illinois University, 2005

7. Appending Output Syntax: command >> file
The C Shell
Appending Output
Syntax: command >> file
adds 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
Build the file ‘usage-status’ from the output of the ‘date’, ‘ls’, and ‘du’ commands
CSCI The UNIX System
Copyright Department of Computer Science, Northern Illinois University, 2005

8. Summary: Redirections and Pipe
The C Shell
Summary: Redirections and Pipe
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
CSCI The UNIX System
Copyright Department of Computer Science, Northern Illinois University, 2005