Shell tricks

We will learn about two shell features that can save you a lot of typing.

Expansion

command PREFIX{aaa,bbb}POSTFIX is expanded to command PREFIXaaaPOSTFIX PREFIXbbbPOSTFIX. It also works with more than two arguments inside the curly brackets {}.

This is especially useful when dealing with paths. Here are some examples:

• mkdir -p dir/sub{1,2,3} ➡️ mkdir -p dir/sub1 dir/sub2 dir/sub3
• touch dir/sub1/file{1,2}.txt ➡️ touch dir/sub1/file1.txt dir/sub1/file2.txt
• cp dir/sub1/file1.txt{,.bak} ➡️ cp dir/sub1/file1.txt dir/sub1/file1.txt.bak

Note: The additional extension .bak is sometimes used for backups.

Globbing

The globbing asterisk * is used for expanding to every possible path in a directory.

It is best explained using examples:

• cat *.sh prints the content of all files ending with .sh in the current directory.
• mv dir1/* dir2 moves all visible files and directories from dir1 to dir2.
• mv dir1/.* dir2 moves all hidden files and directories from dir1 to dir2.
• mv dir1/{,.}* dir2 expands to mv dir1/* dir1/.* dir2 and therefore moves all visible and hidden files and directories from dir1 to dir2.

Note: Fish can expand a globbing when pressing Tab after an asterisk * (but it is not always helpful).