Linux Overview

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Overview

Core unix is a collection of tiny commands, each of which performs a set, singular, and well-defined task. Creeping featurism can cripple and distort the purpose of a program

Think of most UNIX commands as if they were tools you pull from a tool bag. You don't find combination screwdriver-hammer tools, and you won't find hybrid and agglomerated commands like that in the core UNIX utility set.

Although, that that being said, Rube Goldberg would probably be running UNIX.

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Core UNIX Commands

To search the man system for a string run man -k string.

1. vi
2. sed
3. find
4. grep
5. dd
6. ln
7. ksh
8. regexp
9. date
10. csplit

 

Essential Sysadmin Tools

1. screen
2. wget
3. lsof
4. fanout
5. xml
6. snort
7. Netcat
8. Knoppix
9. NTOP
10. Nagios
11. nmap
12. gcc
13. make
14. gdb
15. Ethereal

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The for loop

The for loop is my favorite. I can take a list of files in a directory, or a list of words in a file, and loop through them, applying commands as I go. For example:

     for i in `ls *.csv`
     do
        echo $i
        sed "s/oldstring/newstring/g" $i > $i.new
        mv $i.new $i
     done

To run the above either type it in at the command line or insert the commands into a file, say tmp.sh, and then run that file with the following command:

nohup sh ./tmp.sh > tmp.log 2>tmp.err &

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The shell's file tests [ test file ]

See also: Script examples

Test	True if
-r	file exists and is readable
-w	file exists and is writable
-x	file exists and is executable
-f	file exists and is a regular file
-d	file exists and is a directory
-h	file exists and is a symbolic link
-d	file exists and is a character special file
-b	file exists and is a block special file
-s	file exists and has a file size greater than 0

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The shell's string tests

Test	True if
-z string	file string's length is 0
-n string	file string's length is not 0
str1 = str2	file strings are identical
str1 != str2	file strings are not identical
string	file string is not null

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Return Values

    if grep $x $xfile >/dev/null; then
         echo "Found it"
    else
         echo "Not found"
    fi

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Working Session: Dump data for a UNIX to AS400 migration

     $ sh ./dumpas400.sh > dump.log 2>dump.err &

     $ ls -l dump*
     -rw-rw-rw-   1 lawadm     lawson        4955 Mar 19 17:50 dump.err
     -rw-rw-rw-   1 lawadm     lawson          95 Mar 19 17:50 dump.log
     -rwxrwxrwx   1 lawadm     lawson         750 Mar 19 17:47 dump.sh

     $ tail dump.err
     Dumping GLACCTREL ...     75 Records
     Dumping GLADDRESS ...     10 Records
     Dumping GLCHART ...      6 Records
     Dumping GLCHARTDTL ...   3$ 0

     $ tail dump.log
     GLADDRESS
     GLCHART
     GLCHARTDTL
     GLCHARTSUM
     GLCODES
     GLCOMPREL
     GLICHART
     GLINTCO
     GLITRANS
     GLMASTER

 

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