Bash Cheat Sheet - SniferL4bs
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This document provides a cheat sheet on Bash scripting strings, operators, conditionals, integers, arrays, and loops. It describes string operators like parameter expansion and substring extraction. Condition tests for strings, files, and integers are outlined. Integer operations and conditional expressions are defined. The cheat sheet explains how to store and recall elements of arrays. Finally, it provides the syntax for common loop constructs like if/else, for, while, select, case, and until in Bash scripts.
![Condition Tests
Example: [ condition ]
Operator
True if
string1 = string 2
string1 matches string2
string1 != string 2
string1 does not match string2
string1 == string2
string1 is equal to string2
string1 !== string2
string1 is not equal to string2
string1 < string2
string1 is less than string2
string1 > string2
string1 is greater than string2
-n string1
string1 is not null
-z string1
string1 is null
&&
Logical AND
||
Logical OR
File Condition T
ests
Example: [ condition ]
Operator
True If
-a file
file exists
-d file
file exists and is a directory
-f file
file exists and is a regular file (e.g. is not a directory)
-r file
You have read permission on file. Can also be used with -w, -x for
write, and execute permissions respectively.
-s file
file exists and is not empty
file1 -nt file2
file1 is newer than file2
file1 -ot file2
file1 is older than file2](https://image.slidesharecdn.com/bashcheatsheet-140101135331-phpapp01/85/Bash-Cheat-Sheet-SniferL4bs-2-320.jpg)
![Integers
Setting Variables
declare can be used with options to set variables. For example: declare -i var1
-a
-i
-r
The variables are treated as arrays
The variables are treated as integers
Makes the variable read only
Operators
Use with double parenthesis. For example: echo $((var1++))
Operator
Meaning
++
Increment by one (prefix and postfix)
--
Decrement by one (prefix and postfix)
+, -, *, /
Add, subtract, multiply, and divide respectively
%
Remainder of division
**
Exponentiation
Conditionals
Integer variables take different conditionals than strings. For example: [ 3 -gt 2 ]
Operator
Meaning
-lt
Less than
-gt
Greater than
-le
Less than or equal to
-ge
Greater than or equal to
-eq
Equal to
-ne
Not equal to
Alternately, the regular operators can be called out, provided the expression is surrounded by
double parenthesis: eg: echo $(( (3 > 2) && (4 <= 1) ))](https://image.slidesharecdn.com/bashcheatsheet-140101135331-phpapp01/85/Bash-Cheat-Sheet-SniferL4bs-3-320.jpg)
![Arrays
Storing
array1[2]=value
Will store value as the second element of array1
array1=([2]=value [0]=..) Will store value as the second element of array1...
array1=(value value)
Will store values in array1 in the order they are entered
Recalling
${array1[0]}
${array1[*]}
${!array1[*]}
${#array1[1]}
${#array1[*]}
will return element 0 of array1
will return all elements of array1
will return occupied array1
will return the length of element 1
will return the length of the array1
Loops
If
For
if condition
then
statements
[elif condition
then
statements]
[else
statements]
fi
Select
select name [in list]
do
statements that
can use $name
done
for name [in list]
do
statements that can use
$name
done
While
while condition
do
statements
done
Case
case expression in
pattern1 )
statements ;;
pattern2 )
statements ;;
esac](https://image.slidesharecdn.com/bashcheatsheet-140101135331-phpapp01/85/Bash-Cheat-Sheet-SniferL4bs-4-320.jpg)
Bash Cheat Sheet - SniferL4bs
- 1. Bash Cheat Sheet Strings: Operators ${varname:-word} If varname exists and isn't null, return its value; otherwise return word. ${varname:=word} If varname exists and isn't null, return its value; otherwise set it to word and then return its value. ${varname:?message} If varname exists and isn't null, return its value; otherwise print varname: followed by message, and abort the current command or script. ${varname:+word} If varname exists and isn't null, return word; otherwise return null. ${varname:offset:length} Performs substring expansion. It returns the substring of $varname starting at offset and up to length characters. If length is omitted substring expansion starts at offset and continues to end of $varname Pattern Matching ${variable#pattern} If the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest. ${variable##pattern} If the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest. ${variable%pattern} If the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest. ${variable%%pattern} If the pattern matches the end of the variable's value, delete the longest part that matches and return the rest. ${variable/pattern/string} The longest match to pattern in variable is replaced by string. ${variable//pattern/string} All matches to pattern in variable are replaced by string
- 2. Condition Tests Example: [ condition ] Operator True if string1 = string 2 string1 matches string2 string1 != string 2 string1 does not match string2 string1 == string2 string1 is equal to string2 string1 !== string2 string1 is not equal to string2 string1 < string2 string1 is less than string2 string1 > string2 string1 is greater than string2 -n string1 string1 is not null -z string1 string1 is null && Logical AND || Logical OR File Condition T ests Example: [ condition ] Operator True If -a file file exists -d file file exists and is a directory -f file file exists and is a regular file (e.g. is not a directory) -r file You have read permission on file. Can also be used with -w, -x for write, and execute permissions respectively. -s file file exists and is not empty file1 -nt file2 file1 is newer than file2 file1 -ot file2 file1 is older than file2
- 3. Integers Setting Variables declare can be used with options to set variables. For example: declare -i var1 -a -i -r The variables are treated as arrays The variables are treated as integers Makes the variable read only Operators Use with double parenthesis. For example: echo $((var1++)) Operator Meaning ++ Increment by one (prefix and postfix) -- Decrement by one (prefix and postfix) +, -, *, / Add, subtract, multiply, and divide respectively % Remainder of division ** Exponentiation Conditionals Integer variables take different conditionals than strings. For example: [ 3 -gt 2 ] Operator Meaning -lt Less than -gt Greater than -le Less than or equal to -ge Greater than or equal to -eq Equal to -ne Not equal to Alternately, the regular operators can be called out, provided the expression is surrounded by double parenthesis: eg: echo $(( (3 > 2) && (4 <= 1) ))
- 4. Arrays Storing array1[2]=value Will store value as the second element of array1 array1=([2]=value [0]=..) Will store value as the second element of array1... array1=(value value) Will store values in array1 in the order they are entered Recalling ${array1[0]} ${array1[*]} ${!array1[*]} ${#array1[1]} ${#array1[*]} will return element 0 of array1 will return all elements of array1 will return occupied array1 will return the length of element 1 will return the length of the array1 Loops If For if condition then statements [elif condition then statements] [else statements] fi Select select name [in list] do statements that can use $name done for name [in list] do statements that can use $name done While while condition do statements done Case case expression in pattern1 ) statements ;; pattern2 ) statements ;; esac