Working with the Unix OS

Unix Shells
Shell Program Variables
Several special variable names are available within shell programs.
$0 Program name
$1 $2 ...$9 Program arguments
$# Number of arguments
$* Same as "$1 $2 ...$9"
$@
Like $* except "$@" will put double quotes around each argument.
$@" --> "$1" "$2"..."$n"
$? Exit status of the last command.
$$ Shell process number. Uniquely identifies the process. Often used for temporary
file names which reside in the /tmp directory which is shared by everyone.
e.g. /tmp/lsout$$
Inputs and Outputs to/from a Process
Inputs
Files
Stdin
Program name
Arguments
Exported environment
variables
Outputs
Files
Stdout/Stderr
Exit status
Unix Shell Examples
! ZLESS
$ vi zless
-------Enter using vi editor-------
#!/bin/sh
# @(#)zless - browse compressed files
zcat $* | less
-----------------------------------
$ chmod ug+x zless # make shell script executable
$ zless ass1.c.Z
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
SOLARIS: zless is not provided
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
! MKSHAR
#!/bin/sh
# @(#)mkshar - creates shell archives from list of files
# shell archives use the "here document" facility to
# store the contents of one or more files.
# shell archives can be executed by shell to create
# the original archived files. They are typically
# used to send files by electronic mail or news.
for file
do
echo "cat > $file