UNIX Programming Environment

##Chapter.1 Beginners

###1.1 Getting started

RETURN key:

CTRL-m

no more input:

CTRL-d

rings the bell:

CTRL-g

backspace:

CTRL-h

tab:

CTRL-i

break:

CTRL-c

which terminal:

who am i

erase one word:

CTRL-w

erase the entire line:

CTRL-u

Stop output:

CTRL-s

resume

CTRL-q

###1.2 Files and common commands

ls

-t  #time order
-l  #long listing
-u  #when is used
-r  #reverse the order

word count

wc

compare

cmp
diff

###1.4 Shell

####Filename shorthand any string of characters:

*

range of letters or digits

[1-46-9]
[a-z]

any single character

?

turn off the special meaning

ls '?'
ls \?

####Input-output redirection

output to file

command >filename   #overwritting
command >>filename  #appending

take input from a file

command <filename

####Processes

no hangup:

nohup command &

lower priority

nice command &

start command at some time

at <time>   #2130 930pm
command1
command2
...
CTRL-d

##Chapter.2 The File System

###2.1 Basics of files octal dump

od -c   #character
od -b   #octal numbers
od -x   #hex numbers

###2.2 What’s in a file ###2.3 Directories and filenames

disc space used(listing all the files in current directory, pipe it to grep to find a specific file)

du
du -a   #all files in a directory

###2.4 Permissions 3 kinds of permissions:

read, write, execute

different people:

you, group, others

permission string:

-   indicates it's an ordinary file
d   indicates it's a directory
rws s: when the command is run, it is to be given the permissions corresponding to the file owner

directory permission:

r   "read" e.g. ls
w   "write" create and delete files in this dir
    even if you don't have write permission to that file, you can delete it
x   "search" 

chmod

octal:  4 for read, 2 for write and 1 for execute
+:      turns a permission on
-:      turns a permission off

changing permissions on the directory doesn’t change its modification date

###2.5 Inodes
three times:

modified(written) time, used(read or executed) time, (permission) changed time

more on ls

ls -t   #sorts the file according to time(default last modification)
-u      #used time
-c      #changed time
ls -i   #the i-number in decimal

###2.6 The directory hierarchy ###2.7 Device

permission string:

c   #stands for character
b   #stands for block

disc free space:

df

the black hole:

/dev/null

##Chapter.3 Using the Shell

###3.1 Command line structure

tee command: save intermediate output to a file

A timer:

(sleep 300; echo Tea is ready) &    # echo in 5 mins

###3.2 Metacharcters

*   #any string
?   #any single character
[0-9a-z]    #character from range

`command`   output replaces `command`
(command)   run command in a sub-shell
{command}   run command in current shell

$1, $2  first, second argument

'...'   literally
"..."   literally after $, `...` and \ interpreted

p1 && p2    run p1; if successful, run p2
p1 || p2    run p1; if unsuccessful, run p2

###3.3 Creating new commands

###3.4 Command arguments and parameters

###3.5 Program output as arguments

###3.6 Shell variables

runs command in current shell:

.command

export: make the value of a variable accessible in sub-shells

###3.7 More on I/O redirection

direct the standard error output into a file

command 2>filename

put the standard error on the same stream as the standard output

command >filename 2>&1

###3.8 Looping in shell programs

###3.9 bundle: putting it all together

# bundle: group files into distribution package

echo '# To unbundle, sh this file'

for i
do
    echo "echo $i 1>&2"
    echo "cat >$i <<'End of $i'"
    cat $i
    echo "End of $i"
done

Chapter.4 Filters

###4.1 The grep family

grep -n #print line numbers
grep -v #invert the sense of the test
grep -y #smart case matching

always a good idea to enclose grep patterns in single quotes

regular expressions:

[^0-9]  #any non-digit
.       #match any one character
*       #closure operator- any number(including 0) of successive matches
.*      #anything up to a new line
.*x     #anything end with x

####grep family: fgrep, egrep

###4.2 Other filters

####sort

sort -f #case insensitive
sort -d #letters, digits and blanks only
sort -n #by numeric value
sort -r #reverse
sort -u #unique

####uniq

uniq -d #only print duplicated
uniq -u #only print unique
uniq -c #number of occurrences

####comm- compare

print 3 columns of output: lines occur only in f1, occur only in f2, occur in both

comm f1 f2

####tr- translate characters

####an idiom

sort | uniq -c | sort -n

###4.3 The stream editor sed

ind- stick a bat at the beginning of each line:

sed 's/^/	/' $*       #Every line
sed '/./s/^/	/' $*   #Non-empty line
sed '/^$/!s/^/	/'  $*  #Non-empty line

###4.4 The awk pattern scanning and processing language

###4.5 Good files and good filters

##Chapter.5 Shell Programming

###5.1 Customizing the cal command

Shell Built-in Variables(P136)

Shell Pattern Matching Rules(P137)

###5.2 Which command is which?

test -f filename || echo 'file 'filename' does not exist'
# is equivalent to
if test ! -f filename
then
    echo 'file 'filename' does not exist'
fi

###5.3 while and until loops: watching for things

”:” is a shell built-in command that does nothing but evaluate its arguments and return “true”.

####Evaluating variables Examine if the variable is defined or not, if not, print message:

${var?message}

Return value if not defined:

${var-value}

Return value and set var to value if not defined:

${var=value}

Return thing if var is defined or nothing:

${var+thing}

###5.4 Traps: catching interrupts

###5.5 Replacing a file: overwrite

sort file -o file
# sorting the file and output to the same file

###5.6 zap: killing processes by name

###5.7 The pick command: blanks vs. arguments

About $* and $@:(P173)

###5.8 The news command: community service messages

5.9 get and put: tracking file changes

5.10 A look back