Datasheet

Task 1.7: Use Streams, Pipes, and Redirection

Don’t modify a user account when that user is logged in; certain changes are

likely to wreak havoc with work the user is doing. Wait for the user to log out,

or if a change must be implemented immediately, ask the user to log out.

Changing the account’s home directory won’t move the files in the directory. To do that,

you must use the cp command. In this case, the -a option to cp will copy the entire directory

tree and preserve ownership, permissions, and other file characteristics. You’ll then delete the

original directory:

# cp -a /home2/dsmith /home/dsmith

# rm -r /home2/dsmith

To be 100 percent safe, though, you might want to check that the new directory contains

all the files it should before deleting the old one. If possible, wait for the user to log in and use

the account before deleting the old directory.

Criteria for Completion

To complete this task, you should have created a new account (tbrown), deleted an old account

(sjones), and changed the home directory location of a third account (dsmith), including mov-

ing its files. The three commands used to perform this task (useradd, userdel, and usermod)

are at the core of Linux account management. The passwd command is also critical in that it

enables you to set a password on new accounts so that they’re usable. File-manipulation com-

mands such as cp and rm help you manage the files that are associated with accounts.

Task 1.7: Use Streams, Pipes,

and Redirection

The command-line tools introduced earlier enable you to interact with your Linux system at the

command line, typing commands and viewing their output. Sometimes, though, you might want

to do more with that output than simply view it; for instance, you might want to store it in a file

or pass it as input to another program. Fortunately, Linux provides the means to do just that. In

Linux, input and output operations are described as streams. Standard input and output streams

may be redirected to send output to or read input from a regular file, or piped between two pro-

grams. These capabilities provide a great deal of flexibility, as you’ll soon learn.

Part of the Unix philosophy to which Linux adheres is, whenever possible, to

do complex things by combining multiple simple tools. Redirection and pipes

help in this task by enabling simple programs to be combined together in

chains, each link feeding off of the output of the preceding link.

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