In one of the great tragedies of computing history, the three main operating system classes chose three different ways to indicate the separation between one line of text and the next one. Two of these are still with us:

• Linux uses a line feed, Unicode code point U+000A, as the line terminator, meaning that each line including the last one in a file has a trailing line feed character.

• Windows uses a carriage return, Unicode code point U+000D followed by a line feed as a two–character line separator, meaning that the last line in a file by convention does not have a trailing carriage return + line feed. This means that a Windows file which ends in a carriage return and line feed has an empty last line.

• The third style, a carriage return terminator, was used by older Apple operating systems.

Synonyms for “line feed” include:

• The abbreviation LF

• The symbol for line feed

• “Newline”, abbreviated as NL

• The symbol for newline

• ASCII/UTF–8 hexadecimal byte value 0A

• “End of line”, abbreviated as EOL

Carriage return is a valid character within a Bash script, but maybe not in the way you might think. Try creating a simple script like this, containing Windows newlines:

$ printf '%s\r\n' '#!/usr/bin/env bash' '(( "$?" == 0 ))' > test.bash

$ chmod u+x test.bash

$ ./test.bash

/usr/bin/env: ‘bash\r’: No such file or directory

That carriage return character is now part of the shebang line! In general Bash will treat carriage return like any other character in your script, so this can wreak various kinds of havoc depending on how the script is run and whether every line has a Windows newline. Say for example you bypass the shebang line:

$ bash test.bash

test.bash: line 2: syntax error in conditional expression

'est.bash: line 2: syntax error near `))

'est.bash: line 2: `(( "$?" == 0 ))