If Statements

Syntax

If statements in gosh follow the standard POSIX shell syntax:

Basic If Statement

if condition
then
    # commands
fi

If-Else Statement

if condition
then
    # commands when true
else
    # commands when false
fi

If-Elif-Else Statement

if condition1
then
    # commands when condition1 is true
elif condition2
then
    # commands when condition2 is true
else
    # commands when all conditions are false
fi

Features

• Basic if-then-else statements with proper condition evaluation
• Multi-line syntax with separate then, else, and fi keywords
• elif branches for multiple conditions
• Integration with test command for numeric, string, and file comparisons
• Function support - if statements work inside user-defined functions
• Variable expansion in conditions
• Return statement handling within if blocks
• Interactive and script support - works in both interactive mode and script files

Test Command Operators

The test command is commonly used with if statements for condition evaluation:

Numeric Comparisons

• -eq - Equal to
• -ne - Not equal to
• -lt - Less than
• -le - Less than or equal to
• -gt - Greater than
• -ge - Greater than or equal to

String Comparisons

• = - String equality
• != - String inequality
• -z - String is empty
• -n - String is not empty

File Tests

• -f - File exists and is a regular file
• -d - File exists and is a directory
• -e - File exists
• -r - File is readable
• -w - File is writable
• -x - File is executable

Examples

Basic Conditional Logic

#!/usr/local/bin/gosh

# Simple numeric comparison
if test 5 -gt 3
then
    echo "5 is greater than 3"
fi

# String comparison
local name="gosh"  # Local variable
if test $name = "gosh"
then
    echo "Welcome to gosh!"
else
    echo "This is not gosh"
fi

Function Argument Checking

#!/usr/local/bin/gosh

check_args() {
    if test $# -eq 0
    then
        echo "No arguments provided"
        return 1
    else
        echo "Received $# arguments"
        return 0
    fi
}

check_args
check_args arg1 arg2

File Backup Script

#!/usr/local/bin/gosh

backup_file() {
    if test $# -eq 0
    then
        echo "Usage: backup_file "
        return 1
    fi
    
    if test -f $1
    then
        local backup_name="$1.backup.$(date +%Y%m%d)"  # Local variable
        cp $1 $backup_name
        echo "Backup created: $backup_name"
    else
        echo "Error: File $1 does not exist"
        return 1
    fi
}

backup_file "important.txt"

System Information Script

#!/usr/local/bin/gosh

check_system() {
    local current_user="$(whoami)"  # Local variable
    local current_dir="$(pwd)"  # Local variable
    
    if test $current_user = "root"
    then
        echo "Warning: Running as root user"
    else
        echo "Running as user: $current_user"
    fi
    
    if test -d $current_dir
    then
        echo "Current directory: $current_dir"
        if test -w $current_dir
        then
            echo "Directory is writable"
        else
            echo "Directory is read-only"
        fi
    fi
}

check_system

Nested If Statements

#!/usr/local/bin/gosh

check_directory() {
    if test -d $1
    then
        echo "Directory $1 exists"
        if test -w $1
        then
            echo "Directory is writable"
            if test -r $1
            then
                echo "Directory is readable"
            else
                echo "Directory is not readable"
            fi
        else
            echo "Directory is read-only"
        fi
    else
        echo "Directory $1 does not exist"
    fi
}

check_directory $1

Important Notes

• Multi-line support: If statements are supported in both script files and interactive mode. In interactive mode, the shell automatically detects when you start an if statement and continues reading lines until you type fi
• Multi-line format: Use separate lines for if, then, else, and fi keywords
• Nested if statements: gosh fully supports nested if statements. You can place if statements inside other if statements, and the parser will correctly match each if with its corresponding fi
• Condition evaluation: Conditions are evaluated using the exit status of commands (0 = true, non-zero = false)
• Variable expansion: Variables are expanded within conditions, so use proper quoting when necessary
• Return statements: Can be used within if blocks in functions to control function exit
• Test command: The test command is the most common way to create conditions