Question

From this web page :

http://tldp.org/LDP/abs/html/abs-guide.html

It’s mentioned the usage of the if bracket then convention which need a space after the semicolon :

;

Command separator [semicolon]. Permits putting two or more commands on the same line.

echo hello; echo there


if [ -x "$filename" ]; then    #  Note the space after the semicolon.
#+                   ^^
  echo "File $filename exists."; cp $filename $filename.bak
else   #                       ^^
  echo "File $filename not found."; touch $filename
fi; echo "File test complete."

Note that the ";" sometimes needs to be escaped.

Does anyone know where is this coming from and if this is needed at all by certain shells?

Answer 1

This has become the style in the last few years:

if [ -x "$filename" ]; then
   echo "hi"
fi

However, back when dinosaurs like Burroughs and Sperry Rand ruled the earth, I learned to write if statements like this:

if [ -x "$filename" ]
then
    echo "hi"
fi

Then, you don’t even need a semicolon.

The new style with then on the same line as the if started in order to emulate the way C and other programming languages did their if statements:

if (! strcmp("foo", "bar")) {
   printf "Strings equal\n";
}

These programming languages put the opening curly brace on the same line as the if.