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- Shell Scripting Tutorial-1 : Introduction
- Shell Scripting Tutorial-2 : Shell, Kernel, Terminal & More
- Shell Scripting Tutorial-3 : View System Date, Calender
- Shell Scripting Tutorial-4 : Create Files & Directories
- Shell Scripting Tutorial-5 : Text Files: Create, Merge & Play
- Shell Scripting Tutorial-6 : Rename & Delete Files & Directories
- Shell Scripting Tutorial-7 : Create Copies, Links to Files & Directories
- Shell Scripting Tutorial-8 : File Permissions
- Shell Scripting Tutorial-9 : See What's In Using 'ls'
- Shell Scripting Tutorial-10: Change File Permissions Using 'chmod'
- Shell Scripting Tutorial-11: Count Lines, Words & Characters Using 'wc'
- Shell Scripting Tutorial-12: Sort
- Shell Scripting Tutorial-13: Cut Through Your Files
- Shell Scripting Tutorial-14: Convert & Copy Files With 'dd'
- Shell Scripting Tutorial-15: Get Help, View Fancy Text & Reduce File Size
- Shell Scripting Tutorial-16: Hello World!
- Shell Scripting Tutorial-17: Use Commands In Your Scripts
- Shell Scripting Tutorial-18: Shell Variables, Grab User Input Using 'read'
- Shell Scripting Tutorial-19: Positional Parameters
- Shell Scripting Tutorial-20: More On Positional Parameters
- Shell Scripting Tutorial-21: Reverse Quotes Or Accent Graves
- Shell Scripting Tutorial-22: Count The Number of Command Line Arguments Using $
- Shell Scripting Tutorial-23: Math On Integers Using 'expr'
- Shell Scripting Tutorial-24: Operator Precedence
- Shell Scripting Tutorial-25: Math On Real Numbers
- Shell Scripting Tutorial-26: Escape Sequences
- Shell Scripting Tutorial-27: Do Cool Things With 'tput'
- Shell Scripting Tutorial-28: 'if-then' Statement in Action
- Shell Scripting Tutorial-29: The 'if-then-else' Statement
- Shell Scripting Tutorial-30: Run Checks on Numbers
- Shell Scripting Tutorial-31: Run Checks On Files
- Shell Scripting Tutorial-32: Append Text to a File Through Shell Script
- Shell Scripting Tutorial-33: Run Checks On Strings
- Shell Scripting Tutorial-34: The 'AND' Logical Operator
- Shell Scripting Tutorial-35: Count The Number of Characters in User's Input in Your Script
- Shell Scripting Tutorial-36: The 'OR' Logical Operator
- Shell Scripting Tutorial-37: The 'case' Statement
- Shell Scripting Tutorial-38: Another Date With 'case' Statement
- Shell Scripting Tutorial-39: The 'while' Loop
- Shell Scripting Tutorial-40: The 'until' Loop
- Shell Scripting Tutorial-41: The 'for' Loop
- Shell Scripting Tutorial-42: Rant & Little Work
- Shell Scripting Tutorial-43: Search Patterns Using 'grep'
- Shell Scripting Tutorial-44: The 'passwd' File Explained
- Shell Scripting Tutorial-45: The Internal Field Separator
- Shell Scripting Tutorial-46: 'passwd' File Revisited
- Shell Scripting Tutorial-47: Reading From a File
- Shell Scripting Tutorial-48: Sleep while you are at work
- Shell Scripting Tutorial-49: Count the number of words & sentences in a text file without using 'wc'
- Shell Scripting Tutorial-50: Fetch & Redirect Man Pages of commands using 'for loop'
- Shell Scripting Tutorial-51: Nested Loops
- Shell Scripting Tutorial-52: The 'break' Statement
- Shell Scripting Tutorial-53: The 'continue' Statement
- Shell Scripting Tutorial-54: More on Metacharacters
- Shell Scripting Tutorial-55: Adding & Removing Users
- Shell Scripting Tutorial-56: Know when users log in Part One
- Shell Scripting Tutorial-57: Know when users log in Part Two
- Shell Scripting Tutorial-58: Know when users log in Final Part
- Shell Scripting Tutorial-59: Communicate with other users using 'write'
- Shell Scripting Tutorial-60: Create Your Own Commands Using Functions
- Shell Scripting Tutorial-61: Executing Multiple Scripts
##Shell Scripting Tutorial-1: Introduction ##
- Install a linux distribution.
Shell is an interface between user and the UNIX Kernel.
UNIX Kernel manages the resources and hardware.
Terminal provides access to shell.
<username>@<machinename>:~$ terminal commands must be lowercase.
| Command | Description |
|---|---|
who am i |
shows user name, terminal number, date |
whoami |
shows only user name |
pwd |
prints the working directory |
##Shell Scripting Tutorial-3: View System Date, Calender ##
calender commands:
| Command | Description |
|---|---|
cal |
prints the calender |
cal 7 2006 |
prints july 2006 |
cal feb 2033 |
prints february 2033 |
date command prints date as Mon Aug 8 14:37:04 EEST 2016.
Output of date command can be customized.
$ date '+DATE: %m-%y%nTIME: %H:%M:%S'
date commands:
| Command | Description |
|---|---|
date |
prints date as "Mon Aug 8 14:37:04 EEST 2016" |
date '+DATE: %m-%y%nTIME: %H:%M:%S' |
prints date as "DATE: 08-16 TIME: 14:40:33" |
##Shell Scripting Tutorial-4: Create Files & Directories ##
touch is used to create empty files.
mkdir is used to create empty folder.
cd is used to navigate inside folders.
| Command | Description |
|---|---|
touch empty_file1 empty_file2 |
creates two empty files |
mkdir folder1 |
creates a folder in working directory |
mkdir Documents/folder1 |
creates a folder in Documents directory |
##Shell Scripting Tutorial-5: Text Files: Create, Merge & Play ##
cat creates file with text.
$ cat > test_file
test_file content bla bla..
cat shows content of the file.
$ cat test_file
$ cat < test_file
| Command | Description |
|---|---|
cat > test_file |
creates file with text |
cat < test_file |
prints the content |
cat test_file |
prints the content |
cat > test_file2 |
creates file with text |
cat test_file test_file2 > merged_test_files |
merge two files |
cat < merged_test_files |
shows both test files' content |
##Shell Scripting Tutorial-6: Rename & Delete Files & Directories ##
mv renames files and directories
mv file1 file2
rm deletes file
rm file
rm -r deletes directory
rm -r directory/
rmdir deletes empty directory
rmdir empty_directory
| Command | Description |
|---|---|
mv file1 file2 |
renames the file |
mv directory1 directory2 |
renames the directory |
rm file2 |
deletes the file |
rm -r directory2 |
deletes the directory |
rmdir empty_directory |
deletes the empty directory |
##Shell Scripting Tutorial-7: Create Copies, Links to Files & Directories ##
cp is used to copy files from one location to other.
cp copies the file mv cuts and pastes the file.
cp file /home/Music/file_new_name
ln creates hard link for a file.
Hard link is replica of original one.
Any changes from old file, also exists in new one.
Removing the original one does not effect new one.
ln old_file new_file
ln -s creates soft link.
Any changes from old file, also exists in new one.
Removing the original makes soft link useless.
ln -s old old_soft
| Command | Description |
|---|---|
cp old_file /home/Music/new_file |
copy files to new location with new name |
ln file hard_file |
creates a hard link |
ln -s file soft_file |
creates a soft link |
##Shell Scripting Tutorial-8: File Permissions ##
owner, group and other are 3 permission part.
read, write and execute are 3 type of permission.
- read: has numeric value "4".
- write: has numeric value "2".
- execute: has numeric value "1".
umask is used to specify permission values.
Assume umask value is 0022.
file permission = 666 - 022 = 644 which means owner(read, write=6), group(read=4), other(read=4)
directory permission = 777 - 022 = 755 which means owner(read, write, execute=7), group/other(read, execute=5)
| Command | Description |
|---|---|
umask |
shows file and directory permission creation base number |
##Shell Scripting Tutorial-9: See What's Using in 'ls' ##
ls shows the list of files and directories.
ls -l shows the following
total 4
-rw-r--r-- 2 joker joker 0 Aug 9 13:58 forrest_village
-rw-r--r-- 2 joker joker 0 Aug 9 13:58 new
-rw-r--r-- 1 joker joker 0 Aug 9 15:10 sample
drwxr-xr-x 2 joker joker 4096 Aug 9 14:05 sdf
"d" letter at the beginnig of the last line shows that it is a directory.
Any "l" letter at the beginning of the line shows that it is a soft link.
Next characters shows the permissions owner(read,write,execute)group(read,write,execute)other(read,write,execute)
Hidden files are created using . at the beginning of the file name.
touch .test
ls -a shows all files in the directory, inclued hidden files.
| Command | Description |
|---|---|
ls |
lists files and directories |
ls -l |
lists files and directories with permissions |
touch .test |
creates a hidden file |
ls -a |
list all files and directories including hidden ones |
##Shell Scripting Tutorial-10: Change File Permissions Using 'chmod' ##
**chmod** changes file permissions.
chmod 777 test gives read, write and execute permissions to owner,group and other
**uname** shows all about machine.
$ uname -a
output:
**Linux joker 3.16.0-38-generic #52~14.04.1-Ubuntu SMP Fri May 8 09:43:57 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux**
| Command | Description |
|---|---|
chmod 777 test |
gives all permissions to all users |
uname -a |
shows all details about machine and kernel |
##Shell Scripting Tutorial-11: Count Lines, Words & Characters Using 'wc' ##
file shows the type of files.
file *
output:
aaa: symbolic link to 'new'
bbb: empty
forrest_village: empty
jazz: ASCII text
new: empty
sdf: directory
**wc file**
output:
4 7 48 file
4 : number of lines
7 : number of words
48: number of characters
wc -l file show line count
wc -w file show word count
wc -c file show character count
| Command | Description |
|---|---|
file * |
shows file types of all files |
wc file |
shows number of lines, words and chracters of file |
wc -l file |
shows number of lines |
wc -w file |
shows number of words |
wc -c file |
shows number of chracters |
##Shell Scripting Tutorial-12: Sort ##
| Command | Description |
|---|---|
sort animals |
sorts alphabetically the lines of file |
##Shell Scripting Tutorial-13: Cut Through Your Files ##
cut uses - as default saperater.
cut -d"-" -f 1,3 file_name
-d: specify the delimeter character
-f: specify the fields that will be printed
| Command | Description |
|---|---|
cut -d"-" 1,3 file_name |
prints the 1 and 3 column of the file, and - is delimeter |
##Shell Scripting Tutorial-14: Convert & Copy Files with 'dd' ##
converts all characters from lowercase to uppercase in a file.
dd if=test of=test1 conv=ucase
converts encoding to european based encoding.
dd if=test of=test2 conv=ebcdic
| Command | Description |
|---|---|
dd if=test of=test1 conv=ucase |
converts all lowercase to uppercase in a new file |
dd if=test of=test2 conv=ebcdic |
converts encoding to european based encoding |
##Shell Scripting Tutorial-15: Get Help, View Fancy Text & Reduce File Size ##
man <command name> shows the help manual of the command.
man cat
exiting manual page by using Q key.
banner my name is mustafa celik
banner "my name is mustafa celik" banner shows 10 character in one line.
reducing the size of a file.
compress -v test
printing compressed file in a readable format.
zcat -v test.Z
uncompressing the compressed file.
uncompress test.Z
| Command | Description |
|---|---|
man <command> |
shows the manuel of the command. Note: use Q key to quit. |
banner some text |
prints fancy text |
banner "some text" |
prints fancy text in one line. Note: limited to 10 character. |
compress -v test |
compresses the test file. |
zcat -v test.Z |
prints the readable version of the compressed file. |
uncompress test.Z |
uncompress the compressed file. |
##Shell Scripting Tutorial-16: Hello World! ##
hello world example is implemented using echo command.
| Command | Description |
|---|---|
echo "Hello World!" |
prints hello world to terminal. |
##Shell Scripting Tutorial-17: Use Command in Your Script ##
Use commands in the script.
pwd
ls -l
banner "The End"
##Shell Scripting Tutorial-18: Shell Variables, Grab User Input Using 'read' ##
Shell scripting has some rules for variables.
- variable names starts with an alphabet or underscore symbol.
- variables are case sensitive.
my_varandMY_VARare different variables.
read is used to get user input from terminal.
echo "Enter your name: "
read name
| Command | Description |
|---|---|
read name |
reads input from user and assign it to name variable |
##Shell Scripting Tutorial-19: Positional Parameters ##
Renaming a file using one positional parameter.
##Shell Scripting Tutorial-20: More on Positional Parameters ##
setting positional parameters from the content of a file.
set cat test this usage is wrong which assigns $1:cat and $2:test
echo $*
"set `cat test`" this assigns file content as parameters
cat test
echo $*
özetle
reverse quotes: ters tirnak isareti
accent grave: tirnak arasinda komut calistirilan kisim
| Command | Description |
|---|---|
set cat test
|
assigns content of test file to positional parameters |
set who am i
|
assigns output of the command to positional parameters |
##Shell Scripting Tutorial-21: Reverse Quotes & Accent Graves ##
set shell scripting is cool
echo $1
echo $2
echo $3
echo $4
| Command | Description |
|---|---|
set word1 word2 word3 |
assigns $1: word1 $2: word2 and $3: word3 |
echo $* |
prints all positional parameters |
##Shell Scripting Tutorial-22: Count the Number of Command Line Arguments Using '$#' ##
Finding number of positional parameters that comes from command line and set command.
set this is video tutorial about shell scripting
echo $#
| Command | Description |
|---|---|
echo $# |
prints the number of parameter. |
##Shell Scripting Tutorial-23: Math on Integers Using 'expr' ##
arithmetic operations on shell script.
"a=30 b=15"
"echo expr $a + $b"
"echo expr $a - $b"
"echo expr $a \* $b"
"echo expr $a / $b"
"echo expr $a % $b"
| Command | Description |
|---|---|
echo expr $a + $b
|
addition |
echo expr $a - $b
|
substraction |
echo expr $a \* $b
|
multiplication |
echo expr $a / $b
|
division |
echo expr $a % $b
|
modular division |
##Shell Scripting Tutorial-24: Operator Precedence ##
/, *, % operations have first priority.
+, - operations have second priority.
echo expr $a \* \( $b + $c \) / $d
| Command | Description |
|---|---|
echo expr $a \* \( $b + $c \) / $d
|
operation precedence using \ |
##Shell Scripting Tutorial-25: Math on Real Numbers ##
bc usage is explained in this tutorial.
echo $a + $b | bc
echo $a - $b | bc
echo $a \* $b | bc
echo $a / $b | bc
| Command | Description |
|---|---|
| `echo $a + $b | bc` |
##Shell Scripting Tutorial-26: Escape Sequences ##
customizing(text color, border etc.) the echo outputs.
- new line: \n ->
echo "hello \nworld" - return: \r ->
echo "hello \rworld"basa donerek üzerine yazar. - tab: \t ->
echo "hello \tworld" - backspace: \b ->
echo "Hey World, \b\b\b\b\b\b\bwhat's up?"bir onceki karakterin uzerine yaziyor. - bold: \033[1m \033[0m ->
echo "\033[1mHey World, what's up?\033[0m"writes the text in bold format - black background: \033[7m \033[0m ->
echo "\033[7mHey World, what's up?\033[0m"prints black background
| Command | Description |
|---|---|
echo "hello \nworld" |
new line |
echo "hello \rworld" |
return character writes from the beginning over the previous print |
echo "hello \tworld" |
tab character |
echo "Hey World, \b\b\b\b\b\b\bwhat's up?" |
backspace comes 1 character back |
echo "\033[1mHey World, what's up?\033[0m" |
bold character |
echo "\033[7mHey World, what's up?\033[0m" |
black background |
##Shell Scripting Tutorial-27: Do Cool Things with 'tput' ##
clearing terminal.
tput clear
determining the number of rows and columns of the terminal.
tput lines shows number of rows.
tput cols shows number of columns.
printing character in bold.
tput bold
positioning the cursor to a specific row and column.
tput cup 15 20
| Command | Description |
|---|---|
tput clear |
clear the terminal |
tput lines |
Total number of rows on screen |
tput cols |
Total number of columns on screen |
tput cup 15 20 |
position cursor to new row and column |
tput bold |
print in bold format |
echo "\033[0mbye bye" |
ends printing in bold |
##Shell Scripting Tutorial-28: 'if-then' Statement in Action ##
terminalde her komut calistiktan sonra, komutun basarili olup olmadigini gosteren bir sayi doner.
bu ciktiyi gormek icin su komut kullanilir:
mkdir new
echo $?
renaming a file using if statement.
if mv source.txt target.txt
then
echo "Your file has been succesfully renamed."
fi
| Command |
|---|
| usage of if-then statement |
if something_true |
then |
echo "condition is correct" |
fi |
##Shell Scripting Tutorial-29: The 'if-then-else' Statement ##
renaming a file using if statement.
if mv source.txt target.txt
then
echo "Your file has been successfully renamed."
else
echo "file has NOT been renamed."
fi
| Command |
|---|
| usage of if-then statement |
if something_true_or_false |
then |
echo "condition is true" |
else |
echo "condition is false" |
fi |
##Shell Scripting Tutorial-30: Run Checks on Numbers ##
if checks statements are following:
num=3
if [ $num -eq 10]
then
echo "it is equal to 10"
elif [ $num -lt 10 ]
then
echo "less than 10"
elif [ $num -gt 10 ]
then
echo "greater than 10"
elif [ $num -le 10 ]
then
echo "less than and equal to 10"
elif [ $num -ge 10 ]
then
echo "greater than and equal to 10"
elif [ $num -ne 10 ]
then
echo "not equal"
| Command | Description |
|---|---|
-eq |
equal |
-lt |
less than |
-gt |
greater than |
-le |
less than and equal |
-ge |
greater than and equal |
-ne |
not equal |
##Shell Scripting Tutorial-31: Run Checks on Files ##
character space file: text files
block space file: video and image files which can not be displayed by text editor
directory space file: folders are also a file
if [ -f $fname ] checks is it file or not.
-f: checks for file
-d: checks for directory
-c: checks for character space file(text file)
-b: checks for block space file(image, video)
-r: checks read permission
-w: checks write permission
-x: checks execute permission
-s: checks if the file size is greater 0 or not
| Command | Description |
|---|---|
if [ -f $fname ] |
checks file or not |
if [ -d $fname ] |
checks directory or not |
if [ -c $fname ] |
checks character space file or not |
if [ -b $fname ] |
checks block space file or not |
if [ -r $fname ] |
checks has read permission or not |
if [ -w $fname ] |
checks has write permission or not |
if [ -x $fname ] |
checks has execute permission or not |
if [ -s $fname ] |
checks size is greater than 0 or not |
##Shell Scripting Tutorial-32: Append Text to a File Through Shell Script ##
usage of the if else statement and file checks command.
example code:
echo "Enter file name:\c"
read fname
if [ -f $fname ]
then
if [ -w $fname ]
then
echo "Type matter to append. To quit press ctrl+d."
cat >> $fname
else
echo "You do not have permission to write."
fi
fi
##Shell Scripting Tutorial-33: Run Checks on Strings ##
string checks:
| Command | Description |
|---|---|
[ "$str1" = "$str2" ] |
checks if string are equal |
[ "$str1" != "$str2" ] |
checks if string are not equal |
[ -n "$str1" |
checks if string length is greater than zero |
[ -z "$str1" ] |
checks if string length is zero |
##Shell Scripting Tutorial-34: Run Checks on StringThe 'AND' Logical Operator ##
-a is the 'AND' operator for shell scripting.
Following if statement checks the variable if it is between 50 and 100.
if [ $num -le 100 -a $num -ge 50 ]
| Command | Description |
|---|---|
if [ $num -le 100 -a $num -ge 50 ] |
usage of AND operator |
##Shell Scripting Tutorial-35: Count the Number of Characters in User's Input in Your Script ##
checking the number of the character of the variable.
if [ 'echo $var | wc -c' -eq 2 ]
| Command | Description |
|---|---|
| `if [ 'echo $var | wc -c' -eq 2 ]` |
##Shell Scripting Tutorial-36: The 'OR' Logical Operator ##
-0 is the 'OR' operator for shell scripting.
Following if statement checks the variable if it is vowel or not.
if [ $var = a -o $var = e -o $var = i -o $var = u -o $var = o ]
| Command | Description |
|---|---|
if [ $var = a -o $var = e -o $var = i -o $var = u -o $var = o ] |
usage of OR operator |
##Shell Scripting Tutorial-37: The 'case' Statement ##
The case statement is the fourth version of the condition statements.
- if
- if else
- elif
- case
usage of case statement:
echo "Enter a character:\c"
read var
case $var in
[a-z])
echo "You entered a lowercase character."
;;
[A-Z])
echo "You entered an uppercase character."
;;
[0-9])
echo "You entered a digit."
;;
?)
echo "You entered a special character."
;;
*)
echo "You entered more than one character."
;;
esac
##Shell Scripting Tutorial-38: Another Date with 'case' Statement ##
Another example of case statement.
echo "Enter a word:\c"
read word
`case $word in` `[aeiou]* | [AEIOU]*)` ` echo "The words begins with a vowel."` ` ;;` `[0-9]*)` ` echo "The words begins with a digit."` ` ;;` `*[0-9])` ` echo "The words ends with a digit."` ` ;;` `???)` ` echo "The words is a 3-letter word."` ` ;;` `*)` ` echo "Something else."` ;; esac
##Shell Scripting Tutorial-39: The 'while' Loop ##
usage of 'while' loop.
display the number 1 to 10.
count=1
while [ $count -le 10 ]
do
echo $count
count=expr $count + 1
done
| Command | Description |
|---|---|
while [ $count -le 10 ] |
usage of while loop |
do |
|
echo $count |
|
done |
##Shell Scripting Tutorial-40: The 'until' Loop ##
usage of until loop.
display the numbers 1 to 10.
count=1
until [ $count -gt 10 ]
do
echo $count
count=expr $count + 1
done
| Command | Description |
|---|---|
until [ $count -gt 10 ] |
usage of until loop |
do |
|
echo $count |
|
done |
##Shell Scripting Tutorial-41: The 'for' Loop ##
usage of for loop.
for loop is pretty different than until and while loop.
| Command | Description |
|---|---|
for item in * |
usage of for loop. * means all items in current directory |
do |
|
... |
|
done |
##Shell Scripting Tutorial-42: Rant & Little Work ##
comparison of real number.
another comparison for floating point numbers.
min=12.45
val=10.35
if [ 1 -eq "$(echo "${val} < ${min}" | bc)" ]
then
min=${val}
fi
echo "$min"
| Command | Description |
|---|---|
[ $a -eq $b ] |
this is for integers and not working for real numbers |
[ "$a" = "$b" ] |
this converts number to string and compares them |
min=12.45 |
another comparison example for floating point numbers |
val=10.35 |
|
| `if [ 1 -eq "$(echo "${val} < ${min}" | bc)" ]` |
then |
|
min=${val} |
|
fi |
|
echo "$min" |
##Shell Scripting Tutorial-43: Search Patterns Using 'grep' ##
Usage of 'grep' command.
grep is same as using ctrl+f option in a file.
grep -i: ignores case sensitivity grep -n: shows line numbers for search results. grep -c: shows the total number of the line that has money. grep -v: shows the grep result for not matching lines.
| Command | Description |
|---|---|
grep money text_file |
search "money" in text_file |
grep -i money text_file |
search "money" in text_file by ignoring case sensitivity. |
grep -i -n money text_file |
search "money" in text_file by ignoring case sensitivity, and shows line numbers |
grep -i -c money text_file |
search "money" in text_file by ignoring case sensitivity, and shows count of money line |
grep -i -v money text_file |
search "money" in text_file by ignoring case sensitivity, and shows the lines that has no money |
##Shell Scripting Tutorial-44: The 'passwd' File Explained ##
Usage of file "passwd".
cat /etc/passwd command shows the content of passwd file.
joker:x:1000:1000:joker,,,:/home/joker:/bin/bash
filed 1 -> joker: user name
field 2 -> x: password is encrypted for the user
field 3 -> 1000: uid (userid). from 1 to 99 id are reserved for predefined accounts
field 4 -> 1000: group id.
field 5 -> joker,,,: the name of the computer
field 6 -> /home/joker: home folder
field 7 -> /bin/bash: shell
| Command | Description |
|---|---|
cat /etc/passwd |
shows info about the accounts of the computer |
joker:x:1000:1000:joker,,,:/home/joker:/bin/bash |
output of the file |
joker |
field 1: username |
x |
field 2: password |
1000 |
field 3: user id |
1000 |
field 4: group id |
joker,,, |
field 5: name of the computer |
/home/joker |
field 6: home folder of the user |
/bin/bash |
field 7: shell |
##Shell Scripting Tutorial-45: The Internal Field Separator ##
Usage of IFS (internal field separator)
set this is the forty fifth tutorial. sets the positional parameter
default IFS character is space. It can be changed as following:
IFS=: so, IFS is changed to :
| Command | Description |
|---|---|
IFS=: |
Internal file separator is changed |
##Shell Scripting Tutorial-46: 'passwd' File Revisited ##
Example of using passwd file, IFS, grep and set command.
echo "Enter Username:\c"
read logname
# takes the line that is associated with the username
line='grep $logname /etc/passwd'
IFS=: # the separator is : in passwd file
set $line
echo "Username:$1"
echo "User ID: $3"
echo "Group ID: $4"
echo "Comment Field: $5"
echo "Home Folder: $6"
echo "Default shell: $7"
##Shell Scripting Tutorial-47: Reading From a File ##
First, file should load to exec, at the same time current settings should be kept.
terminal variable holds the current settings and it assigns back the settings after reading operation.
terminal='tty'
exec < $fname
while read line
do
echo "$line"
done
exec < $terminal
| Command | Description |
|---|---|
terminal='tty' |
takes the current settings of the terminal |
exec < $fname |
loads the file content |
while read line |
reads the line of the exec which is $fname in this case |
##Shell Scripting Tutorial-48: Sleep While You are at Work ##
Usage of sleep command. Sleep makes a time delay on the execution of shell.
| Command | Description |
|---|---|
sleep 5 |
shell execution sleeps 5 seconds |
##Shell Scripting Tutorial-49: Count the number of words & sentences in a text file without using 'wc' ##
An example is ran. ##Shell Scripting Tutorial-50: Fetch & Redirect Man Pages of commands using 'for loop' ##
| Command | Description |
|---|---|
man cat >> helpfile |
appends output of man command to helpfile |
for cmd in 'cat commandlist' |
for loop iteration of a file |
##Shell Scripting Tutorial-51: Nested Loops ##
Example for nested loop.
a=1
while [ $a -le 3 ]
do
b=1
while [ $b -le 3 ]
do
c=1
while [ $c -le 3 ]
do
echo "$a$b$c"
c='expr $c + 1
done
b='expr $b + 1''
done
a='expr $a + 1'
done
##Shell Scripting Tutorial-52: The 'break' Statement ##
break terminates the loop.
| Command | Description |
|---|---|
break |
ends the loop iteration |
##Shell Scripting Tutorial-53: The 'continue' Statement ##
continue sends execution the beginning of the loop.
| Command | Description |
|---|---|
continue |
returns back to start of loop |
##Shell Scripting Tutorial-54: More on Metacharacters ##
Running more than one command a line.
ls ; cal ; banner "mustafa celik"
| Command | Description |
|---|---|
ls ; cal ; banner "hello" |
running more than one command |
grep -i money text_tutorial_54 > pattern && echo "Task was completed." |
&& works if first part is ok |
##Shell Scripting Tutorial-55: Adding & Removing Users ##
by using GUI user can be added and deleted.
| Command | Description |
|---|---|
sudo login |
change the user |
##Shell Scripting Tutorial-56: Know when users log in Part One ##
login example.
##Shell Scripting Tutorial-57: Know when users log in Part Two ##
example of login.
| Command | Description |
|---|---|
grep "$logname" /etc/passwd > /dev/null |
checking the user exists or not |
if [ $? -eq 0 ] |
##Shell Scripting Tutorial-58: Know when users log in Final Part ##
loging example is implemented.
##Shell Scripting Tutorial-59: Communicate with other users using 'write' ##
Both users must be logged in different terminals.
write username the writer command.
mesg -y the receiver command.
finger shows the terminal of other users.
| Command | Description |
|---|---|
write username |
message command |
mesg -y |
receiver command to take messages |
finger |
terminal list for messaging |
##Shell Scripting Tutorial-60: Create Your Own Commands Using Functions ##
following is the function usage.
run the following command to initialize the function:
$ . function_script.sh
youtube()
{
echo "Good Morning."
}
byebye()
{
cal
}
use following command to release the function:
$ unset youtube
| Command | Description |
|---|---|
unset youtube |
removes the function |
##Shell Scripting Tutorial-61: Executing Multiple Scripts ##
Script should run at the last line of the previous script.