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Makefile-tutorial/shell/Bash-Scripting.txt
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-> ls :
List all the file or folder present in the current directory.
Option:
* -l : List all the file and folder with permission, owner,
and group details in form of vertically alinged list.
* -a : Display hidden (.)dotfile as well.
-> pwd :
Print the current directory, present on the terminal.
-> date :
Print the current date and time.
-> chmod :
Used to change the permission of file or folder
Symbol Meaning :
* a : For all (including owner, group and others)
* u : For owner
* g : For group
* o : For others
* r : read permission ( number 4 )
* w : write permission ( number 2 )
* x : execute permission ( number 1 )
Option :
* a+x : Add execute permission for all.
* a-x : Remove execute permission for all.
* 755 : rwx - user , r-x - group, r-x - others
How to use?
chmod a+x "file/folder name"
chmod 755 "file/folder name"
-> echo :
To Print argument on the terminal
Option:
* -n : Not to add newline.
* ".." : String to print
* $PATH : variable ( environment variable, etc. )
-> $PATH environment variable :
Store the paths which help in invoking executable, script, etc,
without specifying whole path, where its present.
How to add path to $PATH?
export PATH=$PATH:$(pwd)
or full path to intended directory.
-> SHABANG (#!/bin/bash)
Tells to use this interpreter to run the script.
Same as /bin/bash ./script
-> Variables :
To stores data and can be changed.
1. Explicit Defination :
VAR=value
COUNT=5
PATH=/var/lib
2. Read command :
read VAR
read COUNT
read PATH
Option :
* -p : to print the parameter before read.
How to use?
read -p "Your name: " NAME
* -s : to hide the input to be taken. Best use
for password.
How to use?
read -sp "Your age: " AGE
3. Command Substitution :
To store the output of the command executed to the variable.
How to use?
VAR=$(pwd) or VAR=`pwd`
How to use variables?
Use $variableName for using variables.
-> For Math Calculation :
1 . let
let RESULT=NUMBER+5
let NUMBER++
let NUMBER--
let NUMBER+=5
let NUMBER-=5
2. (( ))
RESULT=$(( NUMBER + 5 ))
3. []
RESULT=$[ NUMBER + 5 ]
4. expr
RESULT=$(expr $NUMBER + 5)
RESULT=`expr $NUMBER + 5`
RESULT=`expr 2 + 3`
5. bc ( used for floating point number )
RESULT=`echo "$NUMBER * 1.9" | bc`
-> Argument :
$0 - script name
$1 - first argument
$2 - second argument
$n - nth argument
"$@" - all argument, expands as "$1" "$2" "$3"
and so on.
"$*" - all argument as string, "$1c$2c$3",
where c is IFS (Internal field
separator), which is usally whitespace.
$# - arguments count
-> Redirecting and piping:
Redirecting
* STDIN (0) - Standard input (data provided to program)
* STDOUT (1) - Standard output (what program prints, defaultly to the terminal)
* STDERR (2) - Standard error (what error message program prints, defaultly to terminal)
examples:
cat file1.txt > output_from_cat.txt
cat file1.txt 1>output_from_cat.txt
cat file1.txt 2>error.txt
cat file1.txt 1>output_from_cat.txt 2>error.txt
cat file1.txt &> output_from_cat.txt (from both 1 and 2)
cat file1.txt 1> output_from_cat.txt 2>&1(redirecting error to output)
cat file1.txt >> output_from_cat.txt(adding output instead of replacing it)
Piping
output of preceeding program is input to succeeding
program.
Program1 | Program2
examples:
cat file.txt | wc -l
cat file.txt | head -5 | tail -3 | wc -l
-> Exit Status
echo $?
$? will give a return value of previous command.
It's the return value, called EXIT STATUS.
Successfully exiting give 0 value otherwise
non-zero value.
We can exit script using exit command.
exit command can be used with number 0 - 255.
-> If Statement
if[ condition ]; then
....
elif[ condition ]; then
....
elif[ condition ]; then
....
else
....
fi
* AND with if statement ?
if[ condition ] && [ condition ]; then
....
fi
* OR wiht if statement ?
if[ condition ] || [ condition ]; then
....
fi
* Negate if condition
if[ !condition ]; then
....
fi
if![ condition ]; then
....
fi
-> Mathematical comparison:
* Operands
$ -eq equal to
$ -ne not equal to
$ -gt greater than
$ -lt less than
$ -ge greater than or equal to
$ -le less than or equal to
Examples:
if [ $VAR -eq 5 ]; then
if [ $VAR -gt 7 ]; then
if [ $VAR -eq 5 ] && [ $COUNT -ne 1 ]; then
-> String Comaparison
* Comapare two strings
[ "$STR1" = "$STR2" ]
[ "$STR1" != "$STR2" ]
[ "$STR1" = "hello" ]
[ "$STR1" != "hello" ]
* Compare two strings - quotation marks?
Bash can handle it in another way [[ ]]
[[ $STR1 = $STR2 ]]
[[ $STR1 != $STR2 ]]
[[ $STR1 = "hello" ]]
[[ $STR1 != "hello ]]
This is not widely used and most scripts
are using quotation marks with single
brackets
* Test if string is empty
[ -z "$STR1" ] returns true if STR1 holds
an empty string
[[ -z $STR1 ]] possible, but not widely used
[ -n "$STR1" ] returns true if STR1 holds
a non-empty string
[[ -n $STR1 ]] possible, but not widely used
* Alphabetically compare two strings
[[ $STR1 > $STR2 ]]
[[ $STR1 < $STR2 ]]
No choice!!!
* Wildcards
[[ $STR1 == string-with-wildcards ]]
* Regular expression
[[ $STR1 =~ $regex ]]
-> Wildcards (globbing patterns)
|-----------------------------------------------------------------------|
| Symbol | Description | Example | Example matches |
|-----------------------------------------------------------------------|
| ? | Single | hel? | help, hell, |
| | character | | hel1.... |
|-----------------------------------------------------------------------|
| * | Any number of | ca* | car,ca,carpet, |
| | characters | | carpenter,car112.. |
| | (including zero)| | |
|-----------------------------------------------------------------------|
| [] | Single character| file[0-2] | file0,file1,file2 |
| | from range | [hd]ello | hello or dello |
|-----------------------------------------------------------------------|
| {} | Comma seperated | {*.txt, | hello.txt,doc.txt, |
| | terms | *.pdf} | source.pdf, book.pdf|
|-----------------------------------------------------------------------|
| [!] | Any character | file[!1] | file2,file3.... |
| | listed in | | |
| | brackets | | |
|-----------------------------------------------------------------------|
* some useful character classes: (use it within [])
|-------------------------------------------|
| [:upper:] | Uppercase character |
| [:lower:] | Lowercase character |
| [:alpha:] | Alphabetic character |
| [:digit:] | Number character |
| [:alnum:] | Alphanumric character |
| | (alpha + digit) |
| [:space:] | whitespace character |
| | (space, tab, newline) |
|-------------------------------------------|
* [[ $STRING == pattern_with_wildcards ]]
* [[ $STRING == file[0-9].txt ]]
* [[ $STRING == rich* ]]
-> Regular Expressions
|-----------------------------------------------------------|
| Symbol | Description | Example | Example matches |
|-----------------------------------------------------------|
| . | any single | bo.k | book,bo1k, ... |
| | character | | |
|-----------------------------------------------------------|
| * | preceeding | co*l | cl,col,cool, ...|
| | item must | | |
| | match zero | | |
| | or more | | |
| | times | | |
|-----------------------------------------------------------|
| ^ | Start of | ^hello | line starting |
| | the line | | with hello |
| | marker | | |
|-----------------------------------------------------------|
| $ | End of the | hello$ | line ending |
| | line marker | | with hello |
|-----------------------------------------------------------|
| [] | Any one of | coo[kl] | cook or cool |
| | of character| | |
| | enclosed in[]| | |
|-----------------------------------------------------------|
| [-] | Any character| file[1-3]| file1,file2,file3|
| | within the | | |
| | range | | |
|-----------------------------------------------------------|
| [^] | Any character| file[^0 | file8,file9 |
| | except those| 1234567]| |
| | enclosed in | | |
| | brackets | | |
|-----------------------------------------------------------|
| ? | preceeding | colou?r | color,colour |
| | item must | | NOT colouur |
| | one or zero | | |
| | times | | |
|-----------------------------------------------------------|
| + | preceeding | file1+ | file1,file11, |
| | item must | | file111 |
| | match one or | | NOT file |
| | more times | | |
|-----------------------------------------------------------|
| {n} | preceeding | [0-9]{3}| Any three digit:|
| | item must | | 097,256,787,... |
| | match n times | | |
|-----------------------------------------------------------|
| {n,} | Minimum number| [0-9]{3,}| Any three digit |
| | of times the | | 111,097,256,787.|
| | preceeding | | |
| | item should | | |
| | match | | |
|-----------------------------------------------------------|
| {n,m} | Minimum and | [0-9]{1,3}| 1,158,26, ... |
| | maximum number| | NOT 1258,1111,..|
| | of times the | | |
| | preceeding | | |
| | item should | | |
| | match | | |
|-----------------------------------------------------------|
| \ | Escape | hell\.o | hell.o |
| | character - | | NOT:helllo, |
| | escape any of | | hell1o... |
| | the special | | (Usefule with |
| | character, | | grep) |
| | ignore the | | |
| | meaning of | | |
| | them | | |
|-----------------------------------------------------------|
-> Regex in Bash
* [[ $STRING =~ $REGEX ]]
* REGEX="http://.*\.jpg"
* ${BASH_REMATCH[0]} -> part of the STRING which match
REGEX (e.g. http://images.jpg)
* ${BASH_REMATCH[1]} -> part of the REGEX which is
enclosed in first parentheses,
e.g.
REGEX="http://(.*)\.jpg" -> which
would represents as "images"
-> Filesystem Related Tests
|-----------------------------------------------------------------------|
| File Test operators | Description, what is returned |
|-----------------------------------------------------------------------|
| [ -e $VAR ] | True if variable hold existing file (file |
| | or directory) |
|-----------------------------------------------------------------------|
| [ -f $VAR ] | True if variable holds an existing regular |
| | file |
|-----------------------------------------------------------------------|
| [ -d $VAR ] | True if variable holds an existing directory|
|-----------------------------------------------------------------------|
| [ -x $VAR ] | True if variable is an executable file |
|-----------------------------------------------------------------------|
| [ -L $VAR ] | True if variable holds th path of a symlink |
|-----------------------------------------------------------------------|
| [ -r $VAR ] | True if variable holds file that is readable|
|-----------------------------------------------------------------------|
| [ -w $VAR ] | True if variable holds file that is writable|
|-----------------------------------------------------------------------|
* Example:
if [ -f $FILE ]; then
echo File exists
else
echo File does not exists
fi
-> && and ||
*examples
[ $? -eq 0 ] && echo command OK || echo something went wrong
|-----------------| |
if true execute this |
if NOT true |
|--------------------|
-> For loops
for arg in [list]
do
command(s)..
done
* Example
for PLANET in "Mercury Venus Earth"
do
echo $PLANET
done
for file in *.txt
do
$file
done
-> For loops - C style for loops
for ((i=1; i <= 10 ; i++))
do
echo $i
done
-> While loop
while [ condition ]
do
command(s)
done
-> C-style While loop
while (( condition ))
do
command(s)
done
* Example
A=1
LIMIT=10
while (( A < LIMIT )) //no $ here
do
touch $A
let A++
done
-> Reading Files with While loop
while read line
do
command(s)..
done < "$FILENAME"
cat "$FILENAME" |
while read line
do
echo $line
done
-> Case:
case "$VAR" in
"$condition1")
command(s)...
;;
"$condition2")
command(s)...
;;
*)
command(s)..
;;
esac
*Example:
case "$(whoami)" in
"root")
echo you are root
;;
"richard"|"susan")
echo you are user
;;
*)
echo I don't know you
;;
esac
-> shift
It's a command to throw away the parameter count
that is given to the script.
-> getopts:
* easy way how to parse short positional parameters (-f)
* doesn't support long positional parameters ( --help )
* getopts optstring name
-> For examples:
#!/bin/bash
while getopts a:b:cd param; do
case $param in OPTIND is initialized to 1
a) echo "" each time the shell or a
echo "parameter 'a' with argument: $OPTARG" shell script is invoked.
;;
b) echo "parameter 'b' with argument: $OPTARG" getopts places index of the
;; next argument to be
c) echo "parameter 'c' selected (no colon, no argument)" processed into the variable
;; OPTIND
d) echo "parameter 'd' selected (no colon, no argument)"
;;
esac
done
-> getopt:
* parse command options (enhanced)
opts=`getopt -o a::b:cde --long file::,name::,help -- "$@"`
eval set -- "$opts"
#!/bin/bash
echo "All arguments: $@"
opts=`getopt -o a::b:cde --long file::,name:,help -- "$@"`
eval set -- "$opts"
echo "All arguments after getopt: $@"
-> Arrays:
* Declaration
* ARRAY=(value1 value2 .. valueN)
* ARRAY=(one,two,three)
* Calling
* ${ARRAY[0]} #one
* ${ARRAY[1]} #two
* ${ARRAY[2]} #three
* ARRAY=(one,two,three)
${ARRAY[0]} #one
${ARRAY[1]} #two
${ARRAY[2]} #three
${ARRAY[@]} #all items in Arrays
${ARRAY[*]} #all items in array, delimited by first character of IFS
${!ARRAY[@]} #all indexes in the array ( @/* )
${#ARRAY[@]} #number of items in the array ( @/* )
${#ARRAY[0]} #length of item zero
-> Functions
* function_name(){
<commands>
}
* function function_name{
<commands>
}
* Example
| function hello{
| echo hello
| }
|
| echo "output from function hello: "
| hello
| function hello{
| echo hello $1
| return 11
| }
|
| echo "output from function hello: "
| hello richard
| echo "return value from function hello is: $?"
| function hello { function hello{
| name=$1 local name=$1
| echo "hello $name" echo "hello $name"
| } }
|
| echo "enter your name:" echo "enter your name:"
| read name #richard read name #richard
| hello Peter #hello Peter hello Peter #hello Peter
| echo $name #Peter echo $name #richard
-> Comments:
* Single line:
use: #
* Multi-line:
use: : << cmt
This is
multiline Comments
in bash
cmt
-> String in double quotes:
In double quotes the variable value is replaced
but the special character like * (wildcard)
character is not replaced.
Special character is replaced when used without
double quotes and without double quotes use '\'
before it to supress the behaviour of special
characters.
-> source keyword:
source keyword is used to run the shell script
in the same bash shell.
Since, running a shell scripts run the script
in seperate bash shell by default, running it
with source keyword run the script in same bash
shell.
Syntax:
source ./<script-name>
-> := operator:
This operator only used to initialize uninitialized
variable with a value.
Syntax:
hh = 4;
hh := 5;
echo hh
Output:
4
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