The 3 forms Of If Statement In Bash

The aim of this page📝is to define the syntax and conventions of if statements in Bash.

1. notes

• bash IF statements are wordy (compared to posh/python) — look at its syntax

if <TEST>; then
    <PASSED_CODE>
elif <TEST>; then
    <PASSED_CODE>
else
    <FAILED_CODE>
fi

• tradition dictates that then is on the same line with if
• if it is, it also must be separated from if with ;
• but it is not always like this in the wild, then can be found on a new line, too
• you could put the whole block on a single line, separating if, elif, else and fi with ;

2. singleline shell form

• create games folder from the shell, write ok if succeeds, write error when fails
• note required ; separator between statements

>>> if mkdir games; then echo "ok"; else echo "error"; fi;

3. traditional form

• minimalistic check for the presence of an argument with a conditional expression

if [[ ! $1 ]]; then
    echo "Missing Argument"
    exit 1
fi

4. nonconventional form

• each statement is on a new line
• there is no ;

if [[ $size_mb -gt 0 ]]
then
   log "Size of files: $size_mb MB"
elif [[ $size_kb -gt 0 ]]
then
   log "Size of files: $size_kb KB"
else
   log "Size of files: $size_bytes bytes"
fi