Globbing

All three shells support the use of various placeholders (this is known as globbing or file name expansion) in file names. In all three shells, the question mark ? stands for any letter. Bash also supports the following notation:

ls @(letter|readme).txt

This command only lists the letter.txt and readme.txt files. Zsh can do the same, but by default, it only requires the brackets to be specified:

ls (letter|readme).txt

Both shells also allow for more complex conditions inside the brackets.

Zsh also offers what are known as glob qualifiers, with which you can track down very specific file types. For example, ls *(-@) lists all symbolic links that are currently orphaned.

Bash and Zsh can also manipulate strings. For example, ${var:4:2} returns the fifth and sixth characters from the text in the variable var. You can also use both to solve simple arithmetic problems. To add, say, 1 and 2, use the following construct:

sum=$((1+2))

However, the functions for calculating and editing texts by no means offer the capabilities of specialist programs such as bc, sed, and awk.

File Streams

All shells provide the ability to redirect output from and input to program(s) and link them using pipes:

ls -la | grep "readme" | more

As an alternative to the echo command, all shells still offer the built-in printf command, which writes variable contents to a text:

printf "Name: %s Age: %d" $name $age

As in the function of the same name from the C programming language, you put placeholders in at the right places, and the shell replaces them with the values from the variables.

Control Structures

Developers control the flow within a script using appropriate control structures and loops. However, each shell uses a slightly different syntax. Listing 1 shows an example of an if query in Bash, Zsh, and fish.

# Bash and Zsh
if [[ $color == "red" ]]; then
  echo $color
fi
# Zsh
if [[ $color == "red" ]] {
  echo $color
}
# Fish
if test $color = red
 echo $color
end

In addition to the keyword if, all shells also provide a while loop and a for loop. Bash and Zsh even support two different notations of the for loop. However, the control structures and loops that are offered also differ between the shells. For example, Bash and Zsh still offer an until loop, which is missing in fish.

Zsh is the only shell that offers a repeat loop, which repeats a given number of commands. Bash and Zsh also have a select loop that creates a simply designed menu for a selection.