LPIC1 – Study Notes 1

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A few years back I studied the LPIC1 material, and in doing so gained a much better and fundamental understanding of how linux works. Prior to that, I had been picking up bits here and there by reading and following guides on the internet, but this explained to me in a way that I understood much better, what each command was doing or how the linux server works. I wanted to post the study notes I took at the time here in case they were of use to you. This is what I took from the material as I was studying it.

This will be a multi post article and I will link to the next from each article.

Section 1. Command Line Basics

Moving Within the Shell
Ctrl + A
Ctrl + E
Ctrl + P
Ctrl + N
Ctrl + B – move back one space
Ctrl + F – move forward one space

Ctrl + R – Recursive Search
Ctrl + S – Forward Search
Ctrl + G – Cancel

Ctrl + D – [Delete] key
Ctrl + K – Delete from cursor to end of line
Ctrl + X + Backspace – delete from cursor to start of line
Ctrl + U – also delete from cursor to start of line

Transpose (Swap) Text
Ctrl + T – swap the letter under the cursor with the one before it
Esc + T – swap the word under the cursor with the one before it

Change Case
Esc + U – change word to UPPERCASE
Esc + L – Change word to lowercase
Esc + C – Change single character to uppercase

(Esc + U, Esc + L – cursor must be at the start of the word as it only affects characters from the cursor to the end of the word)

Start Default Editor
Ctrl + X then Ctrl + E

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exec When you run a program using exec, rather than running alongside the shell, it replaces the shell. When you close the program, it close the shell too

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xargs
xargs builds a command from its standard input – pipe the output of a find command to it

xargs [options] [command [command-arguments] ]

$ find ./ -name “*~” | xargs –d “\n” rm

 - Find all files under the current directory ending with a ~ and delete them
 - Find outputs each file found on a new line, so the delimiter in xargs is set to \n for new lines (-d “\n”)
 - Other delimiters could be spaces, tabs, etc

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cat
Concatenate – a tool for combining files

$ cat file1.txt file2.txt > file3.txt

-e  (show ends) adds $ to end of each line
-n  numbers each line
-b  numbers only lines with content – avoids blank lines
-s  squeezes concurrent (grouped) blank lines down to just one line

tac  displays files with line order reversed, i.e. line 3 before line 2 before line 1

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join
Combine 2 files by matching entries in one to entries in another. There must be matching (key) entries for this to work

123 Bob 123 listed join 123 Bob listed
456 Alice 456 unlisted —> 456 Alice unlisted

 - By default it uses the first field to match across files
 - Specify another field using -1 or -2 to specify which file, e.g.

join -1 2 -2 4 file1.txt file2.txt

 - (from the first file (-1) use the 2nd field; from the 2nd file (-2) use the 4th field

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paste
Paste merges files, line by line, separating the contents of each file using tabs

paste file1.txt file2.txt
123 Bob 123 listed paste 123 Bob [tab] 123 listed
456 Alice 456 unlisted paste 456 Alice [tab] 456 unlisted

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expand
Convert tabs to spaces
-t n  Convert all tabs to n number of spaces

$ expand –t 1 file.txt

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od
 - Display files (text, image, binary, etc) in octal format
 - Display them in base 8 format
 - Can be used to display in hex, decimal, …

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sort

-f ‐‐ignore-case, usually results are sorted to display uppercase first (ASCII value), but this disables this
-m ‐‐month-sort, sort using 3 letter month abbreviations, i.e. Jan-Dec
-n ‐‐numeric-sort, sort by number
-r ‐‐reverse, sort in reverse order
-k tell it what field you want to sort on (default is the first field)

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split
Splits a file up according to the parameters provided. Requires an output filename to be supplied

-b n splits a file into multiple files, all of a byte size (n) specified
-C n splits files up but doesn’t break across lines, unless the size of the line is greater (in bytes) than specified (n)
-l n splits a file up using the specified number of lines (n)

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unexpand
Converts multiple spaces to tabs

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uniq
Remove duplicate lines

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fmt
Reformat paragraphs. Reformat blocks of text so they display properly on a screen, etc

-w  specify paragraph width (75 = default)

$ fmt –w 100 essay.txt > formatted_essay.txt

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nl
Number lines in text
 - Can be done with ‘cat –b’ for simple results
 - More specialised results are possible with nl

-b Body Numbering Style: using a style format code
-h Header numbering style
-f Footer numbering style
-d=code Set a new page delimiter
-p do not restart numbering at #1 for each page
-n ln/rn/rz number format, where:
  ln = left justified, no leading zeroes
  rn = right justified, no leading zeroes
  rz = right justified, with leading zeroes

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-pr
Printing files

$ pr file.txt

default formatting is for a line printer – 80 character line length, monospaced font

Default includes headers with current date & time, original filename & page number

‐‐numcols generate multi-column output. If lines are too long they are cut or run over into multiple columns
-d ‐‐double-spaced, generate double spaced output
-f ‐‐form-fixed, use form feeds
-l n ‐‐length=’n’ , set page length
-h ‘text’ ‐‐header=’text’, set header text
-t omit the header altogether
-o n ‐‐indent=n, set left and right margins
-w n ‐‐width=n, set the page width

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head
view the first few lines of a file (default = 10)

-c ‐‐bytes=n, display the first n bytes of a file rather than lines
-n ‐‐lines=n, display the first n lines rather than the default (10)

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tail
View the last few lines of a file (default = 10)

-c ‐‐bytes=n, view the last n bytes
-n ‐‐lines=n, view the last n lines
-f ‐‐follow, keep tail open and display new lines as the are added. Very useful for viewing log files
‐‐pid=n give tail the pid of the program to follow, and when the process ends, tail will end also

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Use head and tail in conjunction
To view lines 25-30 of a file:

$ head –n 30 file1.txt | tail –n 6

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less
Page through files

 - Spacebar & B to move pages downwards and backwards
 - Esc – v moves backwards too
 - Arrow keys to move up/down by line
 - /text to search for text
 - Pressing n alone jumps the search forward to next result. Pressing N jumps the search backwards
 - ?text searches backwards for text
 - g# jumps to line #
 - h from within less brings you to less’s internal help dialogue

man pages use less so the above is relevant to navigating these too

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cut
extract portions of input lines & display them on standard output

-b ‐‐bytes=LIST, cut only the specified list of bytes from the input
-c ‐‐characters=LIST, cut specified list of characters from input. Used to give same results as –bytes
-f ‐‐fields=LIST, cut specified list of fields

  – A field is a tab delimited section of a line. You can change this using –d / –delim=char, where char is the character you use to delimit fields
  – cut echoes lines that don’t contain delimiters. Use –s / –only-delimited to only show lines which do contain the delimiter
  – LIST is a way to specify multiple bytes, characters or fields, specified by a number. Can be a single number (4), a closed range (2-4) or open range (-4)(4-)

$ ifconfig eth0 | grep HWaddr | cut –d “ “-f 11

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wc

$ wc file1.txt
2002 24781 169762 file1.txt

2002 lines (new line characters)
24781 words
169762 bytes

-l ‐‐lines, show only line counts
-w ‐‐words, show only word counts
-c ‐‐bytes, show only byte counts
-L ‐‐max-line, show longest line length

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REGEX

Bracket Expressions: [ ] – these match any one character within the brackets
b[io]g = big or bog
does not equal biog
Range Expressions: [ – ] – instead of listing every character that matches, these list the start and end points
a[2-4]z = a2z, a3z, a4z
Any Single Character: The dot (.) represents anything except a new line
a.z = a2z, abz, aQz, …
Start and End of Line: Carat (^) represents start of line
Dollar ($) represents end of line
Repetition Operators: Asterisk (*) represents zero or more occurrences
Plus (+) represents one or more occurrences
Question (?) represents zero or one match only

.  Matches any single character
?  Will be matched zero or one time
*  Will be matched zero or more (multiple) times
+  Will be matched one or more (multiple) times

Multiple Possible Strings: Vertical bar ( | ) seperates two possible matches, i.e. car|truck = either car or truck
Brackets: ( ) these surround subexpressions
Escaping: Use \ to match a special character, i.e. example\.com

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grep
search files for text

-c ‐‐count, count the number of lines matching the pattern/regex
-f ‐‐file=FILE, take pattern/regex input from FILE rather than from the command line
-I ‐‐ignore-case, do case insensitive search
-r ‐‐recursive, search the current directory and all sub-directories. Can also use rgrep
-E ‐‐extended-regexp, use extended regex 
$ grep [-options] regex pattern [files/directories]
$ grep –r eth0 /etc/*

May need to enclose the regex in quotes when using vertical bars & asterisks, in case the shell itself, rather than he grep command, tries to interpret them

$ grep –E “(example\.com | test\.com)+127*” /etc/*

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REDIRECTION
Standard output = the screen

>  Creates a new file from standard output, or overwrites it if not there already
>> Appends standard output to a file, or creates it is not there already
2> Creates a new file from standard error, or overwrites it if there already
&> Creates a new file with both standard output and standard error text, or overwrites existing file
<  Takes specified file as standard input
<< Takes text on following lines as standard input, terminating with Ctrl + D
<> Uses specified file as standard input & standard output
tee tee both displays text to standard output (screen) and also saves it to a specified file. Pipe output from a command to it 
$ ls –lh | tee file.txt

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sed

  – 2 forms:
  – sed [options] –f script-file [input-file]
  – sed [options] ‘script-text’ [input-file]
  – sed modifies contents of files, sending changed file to standard output
  – ‘script-text’ on contents of script-file are the commands for sed to run on
  – ‘script-text’ uses single quotation marks when typed on the command line

Command Addresses Meaning
= 0 or 1 Display the current line number
a\text 0 or 1 Append text to the file
i\text 0 or 1 Insert text into the file
r filename 0 or 1 Append text file filename into the file
c\text range Replace the selected range of lines with text
s\regex\replacement Replace text matching regex with replacement
w file Range Write the current pattern space to the specified file
q 0 or 1 Quit the script but print the current pattern square
Q 0 or 1 Quit the script

  – Addresses are line numbers
  – sed can take no addresses (so it works on the entire file), one address (one line) or a range of addresses
  – To encode the end of a line, ASCII has different ways
  – Unix uses single line feed character, \n
  – Dos/Windows uses carriage return, \r, and line feed

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tr

tr changes individual characters from standard input

$ tr [options] SET1 [SET2]

  – Specify the characters you want replaced in a group, SET1
  – Specify the characters you want them replaced by in SET2
  – Each character in SET1 is replaced by with the respective character in SET2

$ tr L l 

		‘Linux’ becomes ‘linux’


  - SET2 can be shorter than SET1, in which case tr substitutes the last letter in SET2 for the missing letter(s) in SET1


$ tr ABCDE w 

	Changes them all to ‘w’


-t  --truncate-set1, truncate SET1 down to the size of SET2

-d  Make tr delete the characters specified in SET1; SET2 is unneeded in this case


  - Can use shortcuts:

    [:alnum:] – all alpha & numeric

    [:upper:] – all uppercase

    [:lower:] – all lowercase

    [:digit:] – all digits

  - Specify range of characters by using -, i.e. A-M for the letters A to M inclusive
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