Bash – When do you use brace expansion

bashbrace-expansionkshshellzsh

I understand what brace expansion is, but I don't know how best to use it.

When do you use it?
Please teach me some convenient and remarkable examples if you have your own tip.

Best Answer

Brace expansion is very useful if you have long path names. I use it as a quick way to backup a file:

cp /a/really/long/path/to/some/file.txt{,.bak}

will copy /a/really/long/path/to/some/file.txt to /a/really/long/path/to/some/file.txt.bak

You can also use it in a sequence. I once did so to download lots of pages from the web:

wget http://domain.com/book/page{1..5}.html

for i in {1..100}
do
   #do something 100 times
done

Related Solutions

Bash Scripting – How to Create a Sequence with Leading Zeroes Using Brace Expansion

Prefix the first number with a 0 to force each term to have the same width.

$ echo {08..10}
08 09 10

From the bash man page section on Brace Expansion:

Supplied integers may be prefixed with 0 to force each term to have the same width. When either x or y begins with a zero, the shell attempts to force all generated terms to contain the same number of digits, zero-padding where necessary.

Also note that you can use seq with the -w option to equalize width by padding with leading zeroes:

$ seq -w 8 10
08
09
10

$ seq -s " " -w 8 10
08 09 10

If you want more control, you can even specify a printf style format:

$ seq -s " " -f %02g 8 10
08 09 10

Best Answer

Related Solutions

Bash Scripting – How to Create a Sequence with Leading Zeroes Using Brace Expansion

Related Question