matthew@seymour:~$ cat >simple_script <<DONE
> echo ""this is a simple script""
> DONE
matthew@seymour:~$ cat simple_script
echo ""this is a simple script""In this example, the shell feeds the cat command you are typing (input) until
the pattern DONE is recognized. The output file simple_script is then
saved and its contents verified. You can use this same technique in scripts to
create content based on the output of various commands and define an end-of-
input or delimiter.
Piping Data
Many Linux commands can be used in concert in a single, connected
command line to transform data from one form to another. Stringing together
Linux commands in this fashion is known as using or creating pipes. Pipes are
created on the command line with the bar operator (|). For example, you can
use a pipe to perform a complex task from a single command line like this:
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matthew@seymour:~$ find /d2 -name '*.txt' -print | xargs cat | \
tr ' ' '\n' | sort | uniq >output.txt
This example takes the output of the find command to feed the cat
command (via xargs) the names of all text files in the /d2 directory. The
content of all matching files is then fed through the tr command to change
each space in the data stream into a carriage return. The stream of words is
then sorted, and identical adjacent lines are removed using the uniq
command. The output, a raw list of words, is then saved in the file named
output.txt.
Background Processing
The shell allows you to start a command and then launch it into the
background as a process by using an ampersand (&) at the end of a command
line. This technique is often used at the command line of an X terminal
window to start a client and return to the command line. For example, to
launch another terminal window using the xterm client, you can use the
following:
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matthew@seymour:~$ xterm &