Working with the Unix OS

Unix Shells
2. UNIX SHELLS
Back Quote Substitution
One way of viewing the output from a command is as a big long string of characters. Unix shell provides a way to
treat stdout from a command as a string which can be substituted into another command.
Example:
The -l option of grep lists the names of files that contain a pattern.
grep -l 'bug' *.c: outputs names of any *.c files containing the pattern 'bug'.
Say the output is:
file0.c
file3.c
Now using back-quotes '...' we can take this output from "grep" and treat it as a string substituted into the
arguments for the command "vi".
vi 'grep -l 'bug' *.c': edits all *.c files containing the pattern 'bug'
vi file0.c file3.c
Example:
The "tr" command can translate one or more characters into a different set of characters.
PATH=/usr/local/bin:/usr/ucb:/bin:/usr/bin
The following outputs the string $PATH with colons translated into spaces:
echo $PATH | tr : ' ': outputs /usr/local/bin /usr/ucb /bin /usr/bin
We can use "ls" to display all of the system commands in the $PATH directories:
ls ' echo $PATH | tr : ' ' '
Shell Here Documents
When writing shell programs you sometimes want some constant data (e.g. test data) as standard input for a
program. This can be done using "