{"id":184,"date":"2018-10-20T12:00:00","date_gmt":"2018-10-20T04:00:00","guid":{"rendered":"https:\/\/yeslq.com\/201810184.html"},"modified":"2019-05-07T10:43:38","modified_gmt":"2019-05-07T02:43:38","slug":"the-linux-command-line-positiona","status":"publish","type":"post","link":"https:\/\/yeslq.com\/?p=184","title":{"rendered":"The Linux Command Line—Positional Parameters"},"content":{"rendered":"

\nThe Linux Command Line <\/a><\/i>by William Shotts<\/span><\/h1>\n
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\n<\/p>\n
\nWhen we last left our script, it looked something like this:<\/div>\n
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#!\/bin\/bash\n\n# sysinfo_page - A script to produce a system information HTML file\n\n##### Constants\n\nTITLE=\"System Information for $HOSTNAME\"\nRIGHT_NOW=$(date +\"%x %r %Z\")\nTIME_STAMP=\"Updated on $RIGHT_NOW by $USER\"\n\n##### Functions\n\nsystem_info()\n{\n    echo \"<h2>System release info<\/h2>\"\n    echo \"<p>Function not yet implemented<\/p>\"\n\n}   # end of system_info\n\n\nshow_uptime()\n{\n    echo \"<h2>System uptime<\/h2>\"\n    echo \"<pre>\"\n    uptime\n    echo \"<\/pre>\"\n\n}   # end of show_uptime\n\n\ndrive_space()\n{\n    echo \"<h2>Filesystem space<\/h2>\"\n    echo \"<pre>\"\n    df\n    echo \"<\/pre>\"\n\n}   # end of drive_space\n\n\nhome_space()\n{\n    # Only the superuser can get this information\n\n    if [ \"$(id -u)\" = \"0\" ]; then\n        echo \"<h2>Home directory space by user<\/h2>\"\n        echo \"<pre>\"\n        echo \"Bytes Directory\"\n        du -s \/home\/* | sort -nr\n        echo \"<\/pre>\"\n    fi\n\n}   # end of home_space\n\n\n\n##### Main\n\ncat <<- _EOF_\n  <html>\n  <head>\n      <title>$TITLE<\/title>\n  <\/head>\n  <body>\n      <h1>$TITLE<\/h1>\n      <p>$TIME_STAMP<\/p>\n      $(system_info)\n      $(show_uptime)\n      $(drive_space)\n      $(home_space)\n  <\/body>\n  <\/html>\n_EOF_\n\n<\/pre>\n<\/div>\n
\nWe have most things working, but there are several more features I want to add:<\/div>\n
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  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
    \nAll 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 through $9) that contain the contents of the command line.<\/div>\n
    \nLet’s imagine the following command line:<\/div>\n
    \n[me@linuxbox me]$ some_program word1 word2 word3<\/div>\n
    \nIf some_program were a bash shell script, we could read each item on the command line because the positional parameters contain the following:<\/div>\n