Standard I/O and Pipes. Standard Input and Output Linux provides three I/O channels to Programs Standard input (STDIN) - keyboard by default Standard. - презентация

1 Standard I/O and Pipes

2 Standard Input and Output Linux provides three I/O channels to Programs Standard input (STDIN) - keyboard by default Standard output (STDOUT) - terminal window by default Standard error (STDERR) - terminal window by default

3 Redirecting Output to a File STDOUT and STDERR can be redirected to files: command operator filename Supported operators include: > Redirect STDOUT to file 2> Redirect STDERR to file &> Redirect all output to file File contents are overwritten by default. >> appends.

4 Redirecting Output to a File Examples This command generates output and errors when run as non- root: $ ls –l f1.txt > f2.txt (only result is stored not error) Operators can be used to store output and errors: $ ls –l tot.txt 2> f3.txt(only error is stored not the result) $ ls –l tot.txt f1.txt &> f3.txt (concatenates the result and stores in f3.txt)

5 Redirecting STDOUT to a Program (Piping) Pipes (the | character) can connect commands: command1 | command2 Sends STDOUT of command1 to STDIN of command2 instead of the screen. STDERR is not forwarded across pipes Used to combine the functionality of multiple tools command1 | command2 | command3... etc

6 Redirecting STDOUT to a Program Examples less: View input one page at a time: $ ls -l /etc | less Input can be searched with / mail: Send input via $ echo "test " | mail -s "test" lpr : Send input to a printer $ echo "test print" | lpr $ echo "test print" | lpr -P printer_name

7 Combining Output and Errors Some operators affect both STDOUT and STDERR &>: Redirects all output: $ ls -l /etc -name passwd &> file1.txt 2>&1: Redirects STDERR to STDOUT Useful for sending all output through a pipe $ ls -l /etc -name passwd 2>&1 | less (): Combines STDOUTs of multiple programs $ ( cal 2007 ; cal 2008 ) | less

8 Redirecting to Multiple Targets (tee) $ command1 | tee filename | command2 Stores STDOUT of command1 in filename, then pipes to command2 Uses: Troubleshooting complex pipelines Simultaneous viewing and logging of output

9 Redirecting STDIN from a File Redirect standard input with < Some commands can accept data redirected to STDIN from a file: $ tr 'A-Z' 'a-z' < file1.txt This command will translate the uppercase characters in file1.txt to lowercase Equivalent to: $ cat file1.txt | tr 'A-Z' 'a-z'

Hi Jane, > > Please give me a call when you g" title="Sending Multiple Lines to STDIN Redirect multiple lines from keyboard to STDIN with < Hi Jane, > > Please give me a call when you g" class="link_thumb"> 10 Sending Multiple Lines to STDIN Redirect multiple lines from keyboard to STDIN with < Hi Jane, > > Please give me a call when you get in. We may need > to do some maintenance on server1. > > Details when you're on-site, > Boris > END Hi Jane, > > Please give me a call when you g"> Hi Jane, > > Please give me a call when you get in. We may need > to do some maintenance on server1. > > Details when you're on-site, > Boris > END"> Hi Jane, > > Please give me a call when you g" title="Sending Multiple Lines to STDIN Redirect multiple lines from keyboard to STDIN with < Hi Jane, > > Please give me a call when you g">

11 Scripting: for loops Performs actions on each member of a set of values Example: for NAME in joe jane julie do MESSAGE='Projects are due today!' echo $MESSAGE | mail -s Reminder $ADDRESS done Can also use command-output and file lists: for num in $(seq 1 10) Assigns 1-10 to $num seq X Y prints the numbers X through Y for file in *.txt Assigns names of text files to $file