Episode Details

This show has been flagged as Clean by the host.

This series is dedicated to exploring little-known—and occasionally useful—trinkets lurking in the dusty corners of UNIX-like operating systems.

The echo command is very useful—it prints the arguments given to it, followed by a newline character. (The newline is sometimes also called a linefeed character depending on who is writing or speaking, and has the ASCII decimal value 10.) It has many uses, either in a script or interactively on the command line. The echo utility is used to display text, the value of a variable, or the result of a pathname expansion. It can also feed text to another command in a pipeline.

As useful as echo is, it should come as no surprise that it first appeared early on in Bell Laboratories' Second Edition UNIX ¹ in 1972. This initial version accepted no options ² —although the manual page doesn't explicitly say output is followed by a newline character, the description of writing "as a line" seems to imply it. In Seventh Edition UNIX, the manual page ³ makes that clear, and also features the addition of the -n option, which causes echo to print the arguments without a trailing newline character. Eighth Edition UNIX's echo ⁴ gained the -e option, which allows certain escape codes from the C programming language to be used.

These variations caused differences in behavior between different versions of echo . Will running echo -n something on your system output the text "something" without a newline, or "-n something" followed by a newline? Things get even trickier when the command arguments include parameter or pathname expansions. If there are files named "-n" and "something" in the current directory, what does echo * output? Like the previous question, that depends on whether or not your version of echo treats -n as an option. You can't get around this ambiguity by quoting or escaping the "*", because that just causes echo to print a literal asterisk.

Example using GNU utilities on Debian 12; both the "echo" utility and the "echo" builtin of bash recognize "-n" as an option.

$ ls -1
-n
something
$ echo *
something$ #Shell prompt is on the same line because "-n" was treated as an option to echo
$ echo "*"
*

The solution was to create a new utility, which is the first UNIX Curio for today: printf . This command allows a user to print text similar to the way the identically-named function works in the C programming language. You run printf ⁵ followed by a format string, followed by zero or more arguments. No newline characters are printed unless specifically indicated by the format string or the arguments.

To use printf to print "something" without a newline, that would just be printf something . This demonstrates t