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KornShell (ksh) Cheatsheet

A quick reference guide for KornShell (ksh) scripting, covering essential syntax, commands, and features for efficient shell programming.

Ksh Basics & Syntax

Basic Syntax

#!/bin/ksh

Shebang line, specifies the interpreter for the script.

Variable Assignment

variable=value (No spaces around =)
readonly variable=value (Makes the variable read-only)

Variable Usage

$variable or ${variable} (for clarity, especially with concatenation)

Command Substitution

$(command) or command

Comments

# This is a comment

Exit Status

$? - Access the exit status of the last executed command (0 is success).

String Concatenation

string="$var1$var2"

Input/Output

Reading Input

read variable (Reads a line from standard input)

Printing Output

print "message" or echo "message" (Prints to standard output)

Redirecting Output

command > file (Redirect standard output to file, overwriting)
command >> file (Append standard output to file)
command 2> file (Redirect standard error to file)
command &> file (Redirect both standard output and error to file)

Here Documents

cat << EOF text... EOF (Passes multi-line text to a command)

Variables

Types of Variables

String variables (default), integer variables (using integer), arrays (using typeset -a)

Exporting variables

export variable (makes the variable available to subprocesses)

Unsetting a variable

unset variable

Special variables

$0 (Script name), $1, $2, … (Arguments), $# (Number of arguments), $$ (Process ID)

Control Flow

Conditional Statements (if/then/else) 

if [ condition ]; then
  commands
elif [ condition ]; then
  commands
else
  commands
fi

Example:

if [ "$var" = "value" ]; then
  print "Var is value"
fi

Case Statements 

case $variable in
  pattern1) commands ;;
  pattern2) commands ;;
  *) commands ;;
esac

Example:

case $option in
  -a) print "Option A" ;;
  -b) print "Option B" ;;
  *) print "Invalid option" ;;
esac

Loops

For Loop

 
for variable in list; do
  commands
done

Example: for i in 1 2 3; do print $i; done

While Loop

 
while [ condition ]; do
  commands
done

Example:

i=0
while [ $i -lt 5 ]; do
  print $i
  i=$((i+1))
done

Until Loop

 
until [ condition ]; do
  commands
done

Select Loop

 
select variable in list; do
  commands
  break #Important to add break
done

Functions and Arrays

Functions

Defining a Function

 
function_name() {
  commands
}

or

function function_name {
  commands
}

Calling a Function

function_name arg1 arg2

Returning Values

return value (Returns an exit status, 0-255. Use print for other values.)

Local Variables

local variable=value (Declares a variable with local scope)

Arrays

Declaring an Array

typeset -a array_name

Assigning Values

array_name[0]=value1 array_name[1]=value2

Accessing Elements

echo ${array_name[0]}

Array Length

echo ${#array_name[*]} or echo ${#array_name[@]}

All Elements

echo ${array_name[*]} or echo ${array_name[@]}

String Manipulation and Built-in Commands

String Manipulation

Substring Extraction

echo ${variable:offset:length}

String Length

echo ${#variable}

Pattern Replacement

echo ${variable/pattern/replacement} (Replaces first occurrence)
echo ${variable//pattern/replacement} (Replaces all occurrences)

Case Conversion

echo ${variable^^} (Uppercase)
echo ${variable,,} (Lowercase)

Built-in Commands

pwd

Print working directory

cd directory

Change directory

ls

List files and directories

mkdir directory

Create directory

rm file

Remove file

cp source destination

Copy file

mv source destination

Move or rename file

test expression or [ expression ]

Evaluate expression (used in conditionals)
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