{"id":36,"date":"2018-10-20T20:00:00","date_gmt":"2018-10-20T12:00:00","guid":{"rendered":""},"modified":"2018-11-11T16:10:58","modified_gmt":"2018-11-11T08:10:58","slug":"the-linux-command-line-positional-parameters","status":"publish","type":"post","link":"https:\/\/yeslq.com\/?p=36","title":{"rendered":"The Linux Command Line—Positional Parameters"},"content":{"rendered":"

The Linux Command Line <\/a><\/i>by William Shotts<\/span><\/h1>\n

<\/span><\/div>\n
<\/p>\n
When we last left our script, it looked something like this:<\/div>\n
\n
#!\/bin\/bash

# sysinfo_page - A script to produce a system information HTML file

##### Constants

TITLE=\"System Information for $HOSTNAME\"
RIGHT_NOW=$(date +\"%x %r %Z\")
TIME_STAMP=\"Updated on $RIGHT_NOW by $USER\"

##### Functions

system_info()
{
    echo<\/tt> \"<h2>System release info<\/h2>\"
    echo<\/tt> \"<p>Function not yet implemented<\/p>\"

}   # end of system_info


show_uptime()
{
    echo<\/tt> \"<h2>System uptime<\/h2>\"
    echo<\/tt> \"<pre>\"
    uptime
    echo<\/tt> \"<\/pre>\"

}   # end of show_uptime


drive_space()
{
    echo<\/tt> \"<h2>Filesystem space<\/h2>\"
    echo<\/tt> \"<pre>\"
    df
    echo<\/tt> \"<\/pre>\"

}   # end of drive_space


home_space()
{
    # Only the superuser can get this information

    if<\/tt> [<\/tt> \"$(id -u)\" = \"0\" ];<\/tt> then<\/tt>
        echo<\/tt> \"<h2>Home directory space by user<\/h2>\"
        echo<\/tt> \"<pre>\"
        echo<\/tt> \"Bytes Directory\"
        du -s \/home\/* | sort -nr
        echo<\/tt> \"<\/pre>\"
    fi<\/tt>

}   # end of home_space



##### Main

cat <<- _EOF_
  <html>
  <head>
      <title>$TITLE<\/title>
  <\/head>
  <body>
      <h1>$TITLE<\/h1>
      <p>$TIME_STAMP<\/p>
      $(system_info)
      $(show_uptime)
      $(drive_space)
      $(home_space)
  <\/body>
  <\/html>
_EOF_
<\/tt>
<\/pre>\n<\/div>\n
We have most things working, but there are several more features I want to add:<\/div>\n
    \n
  1. I want to specify the name of the output file on the command line, as well as set a default output file name if no name is specified.<\/li>\n
  2. I want to offer an interactive mode that will prompt for a file name and warn the user if the file exists and prompt the user to overwrite it.<\/li>\n
  3. Naturally, we want to have a help option that will display a usage message.<\/li>\n<\/ol>\n
    All of these features involve using command line options and arguments. To handle options on the command line, we use a facility in the shell called positional parameters<\/i>. Positional parameters are a series of special variables ($0<\/tt> through $9<\/tt>) that contain the contents of the command line.<\/div>\n
    Let’s imagine the following command line:<\/div>\n
    [me@linuxbox me]$<\/tt> some_program word1 word2 word3<\/tt><\/div>\n
    If some_program<\/tt> were a bash shell script, we could read each item on the command line because the positional parameters contain the following:<\/div>\n