bash =, ‐ge,‐le or Numeric , string comparison - unix1998/technical_notes GitHub Wiki

Here's a detailed explanation to clarify the correct syntax for numeric comparisons in Bash:

1. Using (( ... )) for arithmetic comparisons:

   • This is specifically designed for arithmetic and supports the standard arithmetic operators like <=, <, >=, >, ==, !=.
   • Example:

     x=3
     if (( x <= 5 )); then
         echo "x is less than or equal to 5"
     fi

2. Using [ ... ] for numeric comparisons:

   • This is the traditional test command in Bash. It uses operators like -lt, -le, -gt, -ge, -eq, -ne.
   • Example:

     x=3
     if [ $x -le 5 ]; then
         echo "x is less than or equal to 5"
     fi

3. Using [[ ... ]] for numeric comparisons:

   • This is an enhanced version of [ ... ]. It supports all the same operators as [ ... ] and more, and it's generally more robust.
   • Example:

     x=3
     if [[ $x -le 5 ]]; then
         echo "x is less than or equal to 5"
     fi

1. For (( ... )):

   • Use for arithmetic comparisons with standard arithmetic operators.
   • Example: if (( x <= 5 )); then ...

2. For [ ... ] and [[ ... ]]:

   • Use for numeric comparisons with test operators.
   • Example: if [ $x -le 5 ]; then ...
   • Example: if [[ $x -le 5 ]]; then ...

Let's review and correct your script:

#!/usr/bin/bash
x=3

# Correct numeric comparisons:
# Using (( ... )) for standard arithmetic operators
if (( x <= 5 )); then  # works
    echo "x is less than or equal to 5"
fi

# Using [ ... ] for test command operators
if [ $x -lt 5 ]; then  # works
    echo "x is less than 5"
fi

# Using [[ ... ]] for test command operators
if [[ $x -lt 5 ]]; then  # works
    echo "x is less than 5"
fi

1. Double Parentheses (( ... )):

   • Use for arithmetic expressions.
   • Supports standard arithmetic operators like <=, <, >=, >, ==, !=.

2. Single Brackets [ ... ] and Double Brackets [[ ... ]]:

   • Use for test expressions.
   • Supports numeric comparison operators like -le, -lt, -ge, -gt, -eq, -ne.

#!/usr/bin/bash
x=3

# Using (( ... )) for arithmetic comparison
if (( x <= 5 )); then
    echo "x is less than or equal to 5"
fi

# Using [ ... ] for numeric comparison
if [ $x -le 5 ]; then
    echo "x is less than or equal to 5"
fi

# Using [[ ... ]] for numeric comparison
if [[ $x -le 5 ]]; then
    echo "x is less than or equal to 5"
fi

This script should work correctly and print the message "x is less than or equal to 5" three times.